texts: Rules to identify the most stable resonance structures

texts:
While studying resonance from this Chemistry LibreTexts article, I found the rules to follow in order to decide which structure is the most stable. Among them:

The structure with the least number of formal charges is more stable
The structure with the least separation of formal charges is more stable.

Firstly I'm not sure how to interpret the "number of formal charges" in rule 1: does it refer to the number of atoms with non-zero formal charge or to the magnitude of each formal charge? It confuses me a bit also because the total number of formal charge (the sum of them) is clearly constant (and equal to the total charge or molecule).

Secondly I don't understand which of these two rules (1 or 2) is more important and can dominate the other one.

For example two possible structures of $\ce{CNS^{-}}$ are
$$\ce{C=N=S}\qquad\ce{C#N-S}$$

The formal charge for the first one are (in order) -2, 1, 0 while for the second one are -1, 1, -1.

The first is preferable according to rule 1 (interpreting it as the number of atoms with non-zero formal charge) while the second is preferable according to rule 2 since the separation of charge is not as strong as in the first structure (I hope I'm understanding correctly rule 2).

Am I reading incorrectly the two rules or is there one that is actually "stronger" than the other?


texts: Reactivity of primary and tertiary alkyl halides

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From USNCO 2004, Q58:

  The reaction between which pair of reactants occurs the fastest for $[\ce{OH-}] = \pu{0.010 M}$?

  (A) $\ce{CH3CH2CH2CH2Cl + OH-}$

  (B) $\ce{(CH3)3CCl + OH-}$

  (C) $\ce{CH3CH2CH2CH2Br + OH-}$

  (D) $\ce{(CH3)3CBr + OH-}$

The following is my thought process:

This reaction occurs through one of the SN2, SN1, E1 or E2 pathways.
All pathways prefer better leaving groups. $\ce{Br-}$ is a better leaving group than $\ce{Cl-}$, hence (A) and (B) can be eliminated.
The nucleophile is strongly basic, so will favor E1 and E2 reactions.

However, I am unable to choose between E1 and E2, and option (D) or option (C), respectively.

Also, if there is any error in my reasoning, could it be pointed out?


texts: Why is fluorine deactivating while OH is not?

texts: Both have 2p-2p overlap and oxygen and fluorine have similar electronegativities but OH is strongly activating while fluorine is deactivating


texts: There have been many successful predictions of MO software. Is there a website or journal dedicated to recording them all?


texts: How does B2Cl4 have two perpendicular c2' axes?

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I have been looking at the symmetry of $\ce{B2Cl4}$ and was cannot understand how it has two perpendicular $C_2'$ axes?

I understand it has a $C_2(z)$, $S_4(z)$ and two dihedral planes bisecting each of the $\ce{Cl-B-Cl}$ bonds. However my book says it also has an additional two $C_2'$ axes in the $x$ and $y$ planes centred at the middle of the $\ce{B-B}$ bond. I just can't see it. Any help? ( I understand it will be difficult online but I would very much appreciate your assistance.


texts: Find the Ionisation Potential and Electron affinity of X

texts:
$N_0/2$ atoms of $X_{(g)}$ are converted into $\ce{X^+_{(g)}}$ by energy $E_1$. $N_0/2$ atoms of $X_{(g)}$ are converted into $\ce{X^-_{(g)}}$ by energy $E_2$.
Hence ionisation potential and electron affinity of $\ce{X_{(g)}}$ per atom are:
I tried solving this by unitary method, which gave ionisation potential and electron affinity as, ${2E_1/N_0}$, ${2E_2/N_0}$ respectively.
But the answer given is  ${2E_1/N_0}$, ${2(E_2-E_1)/N_0}$
Can anyone please tell me where I went wrong and help me with the solution. Thanks in advance!


texts: Is there an A value for the carbaldehyde and vinyl groups?

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A methylene ($\ce{=CH_2}$) group ist sterically less hindered than a methyl ($\ce{CH_3}$) group.

I'm wondering if the carbonyl ($\ce{C=O}$) group is sterically more or less larger than a methylene ($\ce{=CH_2}$) group.

Bond length: ($\ce{C=O}$) is shorter than ($\ce{C=C}$) [1]
Diaxial i.a.: Me//H is larger than Me//n(O) (0.9 vs. 0.4 kcal/mol; no ref. for the 2nd value)

While the shorter distance makes the carbonyl more sterically, the lone pairs are less sterically than the Hydrogens of methylene. I think this effect is larger and hence a carbonyl to be more sterically hindered than a methylene group.

The A-values gives the energetical difference of a monosubstituted cyclohexane between the conformation in which the substituent is placed axial (1,3-diaxial interactions, hence higher in energy) versus equatorial.

To reformulate above problem of the sizes I have to set following question:

Comparing the axial conformations of vinylcyclohexane and cyclohexancarbaldehyde: Which molecule is more strained?

Why I am interested in above question?

If we don't assume protonation of a ketone's oxygen, I'd like to know if I have to place the carbonyl axial or equatorial when R=Me.

For R=long alkyl chain it makes sense to place R equatorial, but I'm not sure if a methyl group is also bigger than a carbonyl.

Because I think methylene and carbonyl are almost of the same size from above arguments, and I'm knowing that methyl is bigger than methylene, it sounds logical to me to place the methyl equatorial.

http://evans.rc.fas.harvard.edu/pdf/evans95.pdf


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Cyclobutadiene is very unstable. But, some sources claim that this instability can be attributed to other factors such as ring and angle strain rather than antiaromaticity.

According to some, cyclobutadiene is simply non-aromatic (as opposed to antiaromatic) because it doesn't even have a fully conjugated pi system.

What is/are the real reason(s) for its instability?


texts: How to tell/control whether sodium ethoxide will react by a substitution or elimination pathway?

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Why is the behavior of sodium ethoxide inconsistent?

In a reaction with 1-bromobutane, the anionic part of sodium ethoxide substitutes for $\ce{Br}$:

$$ \ce{CH3CH2CH2CH2Br + C2H5ONa -> CH3CH2CH2CH2-O-CH2CH3}$$

Conversely, in a reaction with 2-bromobutane, the anionic part eliminates $\ce{Br}$:

$$\ce{CH3CH2CHBrCH3 + C2H5ONa -> CH3CH2CH=CH2}$$

I simply don't see how changing the position of $\ce{Br}$ changes the type of reaction. I believe sodium ethoxide, being bulky, must always do elimination, consistent with Rule #3 here.

Given the above: can sodium ethoxide be forced to one type of reaction with a given reactant, by enforcing some reaction conditions?


texts: Can I electrolyze saturated sodium hydroxide?

texts: Can I electrolyze saturated $\ce{NaOH(aq)}$? My guess is that I can't because in the aqueous solution, the concentration of $\ce{OH-}$ is too high and thus there isn't enough $\ce{H+}$ remaining.


texts: Difference Between Betaine & Zwitterion?

texts:
what is difference btw Betaine & Zwitterion, Both having positive and negative charge in a molecule.

How to categorize Zwitterion and Betaine? or both are same.


texts: How significant is air decomposition on formation of nitrogen oxides?

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How significant is $\ce{NO$_x$}$ formation from $\ce{O2}$ (reactant) and $\ce{N2}$ decomposition from simply heating the two as opposed to from $\ce{CO2}$, $\ce{H2O}$, (and $\ce{N2}$) dissociation? In other words, which of the two pathways for $\ce{NO$_x$}$ formation is more significant (I imagine this will vary with equivalence ratio):

$\ce{O}$ and $\ce{N}$ radical from $\ce{N2}$ and $\ce{O2}$ dissociation
$\ce{O}$ radical from $\ce{CO2}$ and $\ce{H2O}$ dissociation with $\ce{N}$ radical

My feeling is that the second becomes more significant as equivalence ratio increases (more fuel means more $\ce{O2}$ is consumed in combustion).


texts: Does aromaticity require a co-planar pi system?

texts:
It's well established that angular twisting can decrease the degree of delocalization across a $\pi$ system (e.g. biphenyl).

Moreover, there's considerable debate about aromaticity in spherical species like $\ce{C_{60}}$.

So let's ask a naive question for discussion. Does aromatic stabilization require a planar delocalized $\pi$ system?


texts: The test of metal hydroxides and metal oxides

texts: Is testing metal oxide different from testing metal hydroxide using a litmus paper?


texts: What does ethylene glycol decompose to when exposed to air for an extended period of time?

texts:
I came across this article on wikipedia on ethylene glycol stating that it decomposes fairly quickly. I was under the impression that ethylene glycol was dangerous to let leach into soil, but I think I'm mistaken as wikipedia states

  it [ethylene glycol] breaks down in air in about 10 days and in water or soil in a few weeks. It enters the environment through the dispersal of ethylene glycol-containing products, especially at airports, where it is used in deicing agents for runways and aeroplanes.

What does it decompose into ($\ce{CO2 + H2O}$?) and what is the mechanism?
Does this mean that a tub of ethylene glycol exposed to air will eventually contain only water?
Is the reaction the same when ethylene glycol penetrates soil around runways?
What is the activation energy for the decomposition and at what temperature will it no longer decompose?


texts: Is there a visible change to baking soda when it reacts with odour?

texts: For example, would a box of baking soda in a fridge lose weight as it absorbs odor? How long would it take to drop 100 g?


texts: Storing oxygen generated via water electrolysis

texts:
I want to create a somewhat pure oxygen gas from electrolyzing water and using sodium bicarbonate as an electrolyte.

How can I harvest the oxygen once it is released from the water, and store it in a container without adding oxygen to the existing air in the container? Meaning that I want pure oxygen in the container and not normal air.


texts: How do we determine the proportions of hydrogen to helium (to other elements) that make up the Sun given the absorption spectra?

texts: I am reading about the composition of the Sun and how it is made up of mostly hydrogen (~90%) and helium (>10%) and other elements with much smaller quantities. The explains that different elements give different absoprtion spectra (different lines) yet I do not understand how the proportions were calculated. Can someone explain this to me?


texts:
I'd like to count the total valence electron of following neutral complex in the ionic counting (=donor-pair):

Electron count:
$$\begin{align} \ce{Cl-} : \ce{6e-} \\ \ce{CH3-}: \ce{2e-} \\ \ce{PPh3} : \ce{2e-} \end{align}$$
which gives $\ce{10e-}$ from these three ligands.

1. Question: How to decide the charge of NO
a) if I set $\ce{NO+}$ the charge of Re must be +, therefore Re(I): d6
b) if I set $\ce{NO-}$ the charge of Re must be 2+, therefore Re(III): d4
Probably only a) gives tetragonal geometry whereas b) gives square-planar geometry, correct?
2. Question: How many electrons for NO (linear/bent)
a) I expect linear NO is in ionic counting way a $\ce{2e-}$ ligand (in covalent counting (=neutral ligand method) a $\ce{3e-}$ donor).
b) I expect bent NO is in ionic counting way a $\ce{2e-}$ ligand (in covalent counting (=neutral ligand method) a 1e donor).
3. Question: Total valence electron number
I remember: When we go from linear to bent the VE number decreases with -2, therefore I expect:
a) linear goes along with $\ce{NO+}$, therefore: 10 + 6 + 2 = 18 VE
b) bent goes along with $\ce{NO-}$, therefore: 10 + 4 + 2 = 16 VE

Especially with 1. Question  I feel pretty uncomfortable.


texts: Why is dimethylglyoximate a bidentate ligand and not a tetradentate ligand?

texts: Why can't the 2 oxygen atoms donate a lone pair and hence become binding sites? Is it because of the angle made by the oxygen and Nitrogen atoms?


texts: Understanding lattice matching of graphene on silver (111) crystal surface and meaning of the √3 x √3 lattice?

texts:
Figure 1 in Ivor Lončarić and Vito Despoja, Phys. Rev. B 90, 075414 Benchmarking van der Waals functionals with noncontact RPA calculations on graphene-Ag(111) (available in Researchgate) shows a schematic of the graphene structure on what I believe is a silver (111) surface.

The caption reads:

  FIG. 1. (Color online) Geometry of the supercell used for our vdW DFT calculations. Upper part: 2 × 2 graphene lattice matched to √3 × √3 Ag(111) lattice. Lower part: Geometry of the supercell in perpendicular direction.

What exactly is a "√3 × √3 Ag(111) lattice" and how exactly does the square root of three come in to this?


texts: Mechanism of reaction between triphenylmethanol and acetyl chloride

texts:
I am reading an old method for making triphenylchloromethane (Org. Synth. 1943, 23, 100):

$\hspace{30 mm}$

When I draw out the structures of the molecules, I see this:

But the $\mathrm{S_N1}$ mechanism doesn't make sense to me since $\ce{OH-}$ is a bad leaving group, and there is nothing to protonate it.


texts:
Some dried, closed coconuts go through carbonation:

The white meat of the coconut becomes disintegrated and smeary
The liquid becomes carbonated with a bit sour-salty tasted coconut water (which reminds the taste of a water and baking soda solution) and a grey to blue color
If the grey-blue liquid given enough time (inside a dried, closed coconut) it could become yellowish and possibly contaminated (I have no idea if the yellow color is due to further carbonation or bacteria)

Given that a dried, closed coconut is a dry and sealed by hard, fibrous shell,
Why dried, closed coconuts go through carbonation?


texts: How can nucleophilic substitution happen at the sp²-hybridised carbon of 4-chloropyridine?

texts:
Why can substitution of the C–Cl bond occur at the sp2-hybridized carbon in the following reaction (taken from Clayden et al., Organic Chemistry (2nd ed.), p 700)?

Ordinarily, SN1- and SN2-type reactions should not occur at sp2 centres, as described here: Why do SN1 and SN2 reaction not occur at sp2 centres?. What is the mechanism of this substitution?


texts: In the Friedel-Craft's alkylation of Toluene with $\ce{CH3Cl}$ in the presence of $\ce{AlCl3}$, the major product was meta - substituted. My teacher gave it to me as an exception. Is there any particular reason behind this reaction ?


texts: How to determine whether two hydrogen are homotopic, diastereotopic, emantiotopic?

texts: I have been learning about nmr and I am confused about how to identify whether two hydrogen on different carbon atoms are homotopic, diastereotopic or emantiotopic. I can do identify this when two hydrogens are attached to same carbon atoms, but when it is different I am lost.I have searched lot on web, but they only include examples of two hydrogens on same atom, not on different ones. So can anyone help determine what the two hydrogen are in these compounds and why ? Thanks.


texts: What surface treatment can turn nickel black?

texts:
Questions:

The detailed surface treatment to turn nickel plated steel black.
The reaction mechanism of the process.

Methods:

(preferred) Anodizing, oxidizing : The only black nickel oxide is $\ce{Ni2O3}$ but I'm not sure if it's suitable for surface protection. I do not know the color or other Ni(II) or Ni(III) compound. There are nickel blackening solution for sale, but I don't know their ingredients.

(not preferred) Electroplating onto the existing nickel: US military have a standard to electroplate black nickel (MIL-P-18317). However this process is quite a fuss.


texts:
I was solving problems related to Carbonyls. The question was:

What would be the product formed after the reduction of this compound
using $\ce{NaBH4}$?

(This is an isomer of Glutaric Anhydride)

I thought that $\ce{NaBH4}$ will reduce the keto group (not the ester) but my book said there will be no reduction. When I asked my instructor he said "Since there are many Oxygen due to steric and some other reason it won't reduce". Won't $\ce{NaBH4}$ reduce that? if-else Why so?


texts: Why Calcium Oxalate is insoluble in acetic acid?

texts:
Calcium oxalate is insoluble in acetic acid, but not it's carbonate, oxide and hydroxide.

From internet, it is even considered as a test to distinguish calcium oxalate from it's carbonate and oxide. The reason from the resources which i had searched, only gave factual reasons such as

High Lattice Energy and
Low solvation energy of $Ca(C_2O_4)$

But intuitively the "short sized" compounds like $CaO$ and $Ca(OH)_2$ must have better packing and more lattice energy, then why much bigger calcium oxalate have higher lattice energy?

Also, i am clueless about how to compare solvation energy of different compounds. I think it has to do with polarity of the solute and the solvent. Any help will be appreciated.

Edit:
I had omitted the relative basicity of oxide, hydroxide and carbonate of calcium but i am more interested in knowing how to compare the lattice energy and solubility of the given compounds.


texts:
so basically it's between primary benzylic carbocation which is known to be stable (benzlic) and secondary carbocation which is allylic... which is also stablized by resonance, i know that usually benzylic is more stable than allylic but when they are same degree.. here its different...
any help?


texts: Preferred IUPAC names for branched unsaturated hydrocarbons (polyenes)?

texts:
What are the preferred IUPAC names for the following three compounds?

Compound 1 is 3-ethenylhexa-1,5-diene. 2 is 3-methylidenehexa-1,5-diene.
But I am still not sure about 3. I have narrowed it down to two choices: 3-ethylidenehexa-1,5-diene or 4-ethenylhexa-1,4-diene.

How do I decide which two of the three double bonds should be in the parent chain, considering that both choices of parent chain have the same number of complex and double bonds?
The information I used is from the following Q&As:
How is a side-group that contains a double bond named?
How do you name an alkene using IUPAC rules if the longest carbon chain in this alkene does not include the double bond?


texts: Why is freezing point depression greater than boiling point elevation for equimolar substances?

texts: I know that the freezing point depression and boiling point elevation are given by the formulas $\Delta\mathrm{T}_{b}=ib\mathrm{K}_{eb}$ and $\Delta\mathrm{T}_{f}=ib\mathrm{K}_{F}.$ It seems that when this formula is applied for equimolar concentrations, the magnitude of freezing point depression is greater than boiling point elevation. Is there a qualitative reason for this? If so, what is it?


texts: Calculate the pH of acetic acid for a 0.02 M solution

texts:
We have a solution $\ce{CH3COOH}$ (acetic acid) with $c=0.02~\mathrm{mol/L}$  and $K_\mathrm a(\ce{CH3COOH}) = 1.8\cdot10^{-5}$. Calculate the $\mathrm{pH}$ of this solution.

All I know is that it is a weak acid and that
$$\mathrm{pH}= \mathrm{p}K_\mathrm a + \log\left(\frac{B}{A}\right).$$
I know $A$ but there is no information about $B$.


texts: Mechanism of formaldehyde / phenol condensation

texts:
The production of bakelite using this method, but with an acid as the catalyst is simple enough; a protonation of the carbonyl oxygen, followed by an electrophilic substitution to the ring. The subsequent cross-linkage formation is the same for both cases, but I can't figure out how the initial reaction
steps would work with a base as the catalyst. Google searches and the texts I have yield nothing.
How would the mechanism proceed with a base as the catalyst here?


texts: in the electrolysis of H₂SO₄ solution, when the concentration is increased why does the current increase even when OH⁻ ions reduce?

texts: During the electrolysis of $\ce{H2SO4}$, $\ce {OH-}$ ions are more reactive than $\ce {SO4^{2-} }$ ions and so they dissociate. as $\ce {OH-}$ ions dissociate, they are the negative ions that carry current. So when the concentration of $\ce {H2SO4}$ is increased, the concentration of $\ce {OH-}$ ions actually reduces, but then the current still increases.


texts: Friedel-Crafts synthesis - How is HCl produced?

texts:
In the mechanism for the acetylation of bromobenzene, how is $\ce{HCl}$ gas produced?

The reactants are acetic anhydride, bromobenzene, $\ce{AlCl3}$ and dichloromethane.

Initially, 4-bromoacetophenone is made, accompanied with (as far as I know) acetic acid and the regeneration of $\ce{AlCl3}$.

How then is $\ce{HCl}$ produced?

To remove the $\ce{AlCl3}$ at the end, 3 $\ce{H2O}$ are added and $\ce{HCl}$ gas is produced then.

I'm trying to think of ways that $\ce{HCl}$ gas is produced prior to that, however. Could a chlorine of the aluminate ion deprotonate the arenium ion?

Could dichloromethane (solvent) donate a $\ce{Cl-}$ to $\ce{AlCl3}$?


texts:
The picture shows the correct answers to this question.

I'm not sure why these answers are correct. $K_p$ only counts with gases, while $K_c$ only counts with aqueous solution + gases. I assumed that any reactions with only gases, or a mix of gases and solids, will have an equal $K_p$ and $K_c$ value, but that is clearly not the case.


texts: Will unused spare razor blades rust if stored for a long time?

texts:
I am considering purchasing 16 razor blade spares for a reduced price, but am unsure if they will be good as new if I were to use them several months from now.

If left alone in the packaging (they come in plastic cartridge cases with one side exposed), will the quality degrade by the time I use the last several (if the blades were replaced monthly)?


texts: Why are two three-membered rings preferred to a single five-membered ring in the reaction of a dihalide with alcoholic KOH?

texts:
The given answer is 1,1-dicyclopropylmethanone:

Step 1 is abstraction of acidic H by the strong base. Then, there's surely going to be anchimeric assistance. But there can be two places where the first carbanion can attack: either at the nearer carbon to form the cyclopropyl group or at the far end one to form a five-membered ring. If it does the former, then this process will be repeated and another cyclopropyl group would be made.

Why not make a more stable five-membered ring in the first step, and then again perform E2 to get 2-ethenylcyclopentan-1-one?


texts: How to determine the purity of lactic acid with titration?

texts:
$\pu{25 mL}$ of $\pu{0.5 \%(w/v)}$ lactic acid ($\ce{C3H6O3}$, molecular mass $\pu{90.1 g mol-1}$, $\mathrm{p}K_{\mathrm{a}} = 3.86$ was neutralised by $\pu{13.1 mL}$ of $\pu{0.1010 M}$ monobasic base. Estimate the end point $\mathrm{pH}$ and calculate the amount of $\ce{C3H6O3}$ in % of the initial one.

This question was part of my final paper. I can't remember the exact words used in the paper for the % part, but I think it is asking for the % purity. I am not sure how to do it.

I calculated the $\mathrm{pH}$ using the formula $\mathrm{pH} = 0.5 (\mathrm{p}K_\mathrm{a} - \log M)$ but I think it is wrong. How is this doen correctly?


texts: Is there a chemical reaction that speeds up when the temprature gets lower?

texts:
We were talking about chemical reaction speed on our chemistry class, and I asked my teacher if there is a chemical reaction that speeds up when the temprature gets lower?
I think this is not everyday chemistry and my teacher didn't have an example for one.


texts: Classifying acid-base reaction between aluminium hydride and lithium hydride

texts:
So I was dealing with a reaction the other day, which is also briefly written in the title:

  $$\ce{AlH3(s) + LiH(aq) -> Li+(aq) + AlH4-(aq)}$$

The strange thing is:

Arrhenius definition cannot explain the reaction, since there is no $\ce{OH-}$ in the reaction formula.
Also Brønsted–Lowry definition cannot explain the reaction, because the stuff which $\ce{LiH}$ gives to $\ce{AlH3}$ is not a proton (hydrogenium, $\ce{H+}$) but a protide (hydride, $\ce{H-}$).
And as far as I know, this is the exact definition of Lewis acid and base written in my chemistry textbook:

  Lewis acid: A substance which can receive unshared electron pair
  Lewis base: A substance which can give unshared electron pair

leading to a conclusion that the above reaction also cannot be explained through the Lewis definition. Below are my questions:

Is there anything wrong in my thought?
Is that really an acid-base reaction? If it is, what kind of acid-base reaction is it?


texts: Question about oxygen and beta carbons in chemical shifts

texts:
Why do the methylene protons that are attached to the beta carbon for the ester group have a chemical shift of +0.6 from oxygen, whereas the methyl protons attached to the beta carbon for the ester group have a chemical shift of +0.5 from oxygen? In other words, why is the oxygen treated as an ester for the methylene protons, but treated as an ether for the methyl protons?

What am I missing? How do I determine when to interpret the beta carbon as an ester or an ether when the carbon is connected to an ester group?


texts: Why is Cubic closed packing called "cubic"?

texts:
How is Cubic Closed Packing "cubic" and also how is hexagonal closed packing "hexagonal"?
I have been thinking over this for a few hours but I am unable to visualise.

I understand that when placing the third layer on top of the second layer ,$2$ situations arise:
If the third layer is placed on the tetrahedral voids it forms an A-B-A-B... type structure which is called hcp (why?)
and If the third layer is placed on the octahedral voids it forms an A-B-C-A-B-C... type structure which is called ccp (why?)


texts: What will be the major product of the reaction between (2R,3R)-2,3-dimethyloxirane and triphenylphosphine?

texts:
Problem

My Attempt

But answer is given B. Where did I go wrong?


texts: Effects of evaporating the solvent of a supersaturated solution

texts: What happens to the solute if you heat up a supersaturated solution? Since a supersaturated solution is already more than saturated with solute and unstable, my theory is that as you heat the supersaturated solution, the solubility limit will have been increased enough to allow all of the solute to dissolve. So technically, the solute does not precipitate out if you heat it enough.


texts: What stable arrangements of hydrogen-bonded water exist in the range of 4-20 water molecules?

texts:
Water clusters made up of various numbers of water molecules have been described.
Are all of these structures theoretical?
What experimental evidence supports any of these structures?

How does the free energy of a particular water cluster (per number of molecules in the cluster) vary from one thermodynamically stable arrangement to another? Is there a general trend, e.g. larger clusters are more stable?

In response to Martin's initial comment:

I am curious about water clusters in the context of receptor-ligand interactions (for example, in protein receptors, enzymes or synthetic host cavities).

In cases where the cavities of these macromolecules is small (for example, a small enzyme active site) what kinds of water clusters are likely to fill this void in the absence of ligand?

Put more broadly, does the structure of the water that is filling the cavity destabilize the receptor in such a way that ligand binding is enhanced?

Considering a hypothetical receptor that is known to bind ligands (whose sizes range between 4 and 20 non-hydrogen atoms) in water, what are likely structures for the encapsulated water cluster that will be displaced by the ligands upon binding?


texts:
Condensed question formulation:

Is there an experimental method to directly visualise the 3D form of a MO wave function, or at least the electron density associated with it?

Full statement:
Molecular orbital theory is a crowning achievement of modern Chemistry: it is by far the most accurate description of chemical bonding we possess and accounts for the vast majority of related phenomena.
An array of evidence exists to confirm predictions from MO theory. Ab initio computational methods such as Hartree-Fock are able to produce a very accurate description of orbital coefficients and energies, which match experimental data for the energies (via photoelectron spectroscopy etc.) or predicted reaction mechanisms/FMO interactions (in kinetic runs).
But do we have any experimental evidence for the shape of MOs?
I'd presume the most feasible way of observing some measure related to the MO wave function $\Psi$ would be to follow a probabilistic approach and try imaging the electron density assumed to be given by $|\Psi|^2$.
Of course, X-ray diffraction first springs to mind; the notorious issue with that being the phase problem. In my superficial understanding: due to the loss of phase information, in going from the XRD pattern to the electron density isosurface (via ab initio methods), essentially we model some initial guess phase and try to fit it to the intensity data.
Since usually the location of nuclei is of far greater practical interest, the formalisms developed to model the phases (e.g. Hansen-Coppens) tend to focus on charge densities localised on each atom (though they are not necessarily of spherical symmetry). This is useful in actually getting the form of the molecule, but produces a picture different to the expected electronic occupation of delocalised MOs.
Is it possible to instead produce the delocalised picture if our ab initio phase guess is based on a RHF calculation? But even if possible, does this have any more legitimacy than the localised picture? I.e. it seems, as far as XRD is concerned, these are equally possible interpretations of the same intensity data where we just forced some phase information as convenient.
Sorry for the long description, this is an in depth presentation of my thoughts on the issue thus far. Any experimental technique/fundamental aspect of MO behaviour I'm missing would be appreciated. But the bottom line is, as stated in the beginning, can we experimentally visualise the shape of MOs or at least their modulus squared?


texts: Long linear molecule with alternating elements?

texts:
In the classic freshman physics text Electricity and Magnetism by Purcell, one of his first examples is the computation of the electrical binding energy of a $\ce{NaCl}$ crystal. He models the crystal in terms of perfect ionic bonding and sums up the energy $q_1q_2/r$ pairwise, computing the $r$ values in three dimensions. (Actually he just gives the first few terms explicitly and then says he carried out the computation numerically on a computer.) The result is $U=-0.8738Ne^2/a$, where $N$ is the number of ions, $a$ is the edge length of the cubic lattice, and the units are cgs, so that the Coulomb constant equals 1.

I thought this was a nice example, but it seemed unfortunate that the actual result could only be found through a fairly complicated numerical computation. I thought it would be nice if I could come up with a similar but simpler example for use with my freshman E&M classes, using a linear molecule with charges $\pm e$ arranged like $\cdots +-+-+-\cdots$. A relatively simple calculation gives an energy of
$$-\frac{Ne^2}{4a}\sum_{k=1}^\infty \frac{1}{k(k-1/2)}.$$

I imagine that the sum can be done in closed form, but anyway it's clearly finite and positive, so that the result is a finite binding energy that has the right sign to keep the system bound.

Is there any molecule that actually has this structure, or something close to it? Googling and asking a chemist in the hall resulted in a variety of examples that are not exactly what I had in mind:

There are various 3-ion molecules such as $\ce{BeF2}$.
You can have long carbon molecules, with hydrogens hanging off of them, but they're not exactly linear, and in any case the carbons are all the same element, so there is no ionic bonding.
Acetylene is linear.

Does nature provide anything like the $+-+-$ chain that I'm describing? Do they not occur because they're too unstable with respect to crumpling up? Could they exist on a substrate (the kind of thing people build using scanning electron microscope probes) or as linear impurities in a bulk solid?

For my purposes, I don't think it really matters whether the bonding is perfect ionic bonding, as long as there is some segregation of charge.

Related:

Why does sulfur, but not oxygen, catenate?
Are long oxygen molecules possible?


texts: Is the strength of hydrogen bonding greater in hydrogen peroxide or water?

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When we compare water and hydrogen peroxide's hydrogen bond strength, which one should have the greater one? I know that peroxide has more hydrogen bonds, but when we compare the strength of each hydrogen bond, which one would be greater?

Online values of the boiling points indicate a greater bond strength in $\ce{H2O2}$. But peroxide has a larger number of hydrogen bonds.

This was a question for comparing bond strength in a test paper.


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The above is a representation of magic acid. The left part is the acid; the right part is the solvent. Why would this combination make for a particularly good acid?

The left part looks like a sulfuric acid derivative, except one of the oxygens has been replaced by an electronegative fluorine. Why can't we replace all the oxygens with fluorines? Wouldn't that make for an even stronger acid through inductive stabilization of negative charge after proton loss?

Also, does the solvent play a role in magic acid's acidity? Does the highly partially positive Sb central atom play a role in stabilizing negative charge on the solute after the solute has been deprotonated?


texts: Storing hydrofluoric acid before the invention of plastics

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The first person to synthesize hydrofluoric acid in large quantities was Carl Wilhelm Scheele in 1771. This acid is known for its ability to corrode glass and metals.

What materials were the containers in which it was stored before the invention of plastics?


texts: The H NMR analysis of the hydrogens in salicylic acid

texts:
I am currently working with an unknown and from the IR spectrum I was able to figure out that the compound I am working with is salicylic acid.

I am looking at the H NMR, but I am a bit confused on the deshielding, integration, and upsheilding of the hydrogens that are near the $\ce{OH}$ and $\ce{COOH}$ groups on the compound. Can someone explain this to me:

Attached is a picture


texts:
I know that $\ce{H2O}$ is neutral.
So how does adding one more hydrogen atom to it make it positive ion ($\ce{H3O+}$)?


texts: Why would the specific heat capacity of water be used as the specific heat capacity of zinc sulfate?

texts: I could not find the specific heat capacity of zinc sulfate and saw that people use water's heat capacity instead. Why is that?


texts: Regarding stability and reactivity of m-xylene

texts:
I came across the following two details about m-xylene:

m-Xylene is thermodynamically most stable compound among o-xylene, m-xylene, and p-xylene.

m-Xylene is most reactive towards nitration and sulphonation among the others.

I did some research and was able to find valid reasons for both the statements, but they still seem to be contradicting each other. How can m-xylene be most stable as well as most reactive at the same time?
Could someone please clarify my doubt and also, add more specific details if required.

UPDATE :
"In m-xylene, the two methyl groups reinforce one another in their activation
of the ring, while in o- and p-xylenes the methyl groups cancel the ring
activation to some extent."

I totally agree with this statement and it clearly explains the reason behind the the reactivity of m-xylene towards nitration and other such reactions.
But I realized that I was considering this statement as the reason behind the stability of m-xylene as well. Reference:
Thermodynamic stability of meta-xylene over ortho- and para-isomers
The reasoning seems to be fitting for both the cases (I do realize now that stability and reactivity are not opposing terms necessarily).
So, is the reason why m-xylene is most thermodynamically stable the same reason why m-xylene is most reactive towards nitration? Could someone please confirm this or add their inputs if I am making some mistake in correlating terms or in my reasoning.


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I was given the following mechanism to prove today post-lecture:

and my attempt is given below.

Now, when the negative charge on the alkene attacks the carbonyl, the electrons are pushed onto the oxygen - which is understandable. My question is: why do these electrons come back down, rather than just be protonated to give an alcohol?


texts: Is there a public database for enthalpy of solution values?

texts: I'm looking for a public database for enthalpy of solution values. The CRC handbook only has selected compounds available. The NIST webbook doesn't appear to have any enthalpy of solution values. Any help would be greatly appreciated!


texts: Can rate of reaction depend on both the reactants and the product?

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In introductory chemical kinetics, an elementary reaction is taken for instance
$$\ce{A -> B}$$
Then, we go on to derive integrated rate kinetics equations for them by assuming
$$\text{rate} = k [\ce{A}]^n$$

Could it possible in a more generic case that :
$\text{rate}=k[\ce{A}]^n [\ce{B}]^m$ and the total order of the reaction be $m+n$? In other words, can the rate of reaction depend on both the molar concentrations of reactants and products independently?


texts: Is it possible to produce sulfuric acid at large scale by oxidizing and hydrating pyrite?

texts:
I was reading The Knowledge by Lewis Dartnell, which is a book about recreating our technology from scratch should we experience a civilization-ending apocalypse. The author thinks that acquiring vanadium catalyst for contact process is too difficult, so his recommendation to produce sulfuric acid is to: (1) bake pyrite, (2) react the sulfur dioxide produced with chlorine gas (electrolyzed from brine), using activated carbon as the catalyst, (3) then react the resulting sulfuryl chloride with water to produce sulfuric acid.

I don't know how hard acquiring vanadium is, but I think it will be easier to replicate the same process happening in acid mine drainage:
$$\ce{2 FeS2 + 7 O2 + 2 H2O → 2 FeSO4 + 2 H2SO4}$$

The iron(II) sulfate can then be baked to produce sulfur trioxide, which can also be processed into sulfuric acid.

I think this method would have been simpler. Am I correct? Is there another simple method of producing sulfuric acid?


texts: Comparison of C=O bond strength in metal carbonyls

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Find the weakest $\ce{C=O}$ bond among $\ce{[Mn(CO)6]+},$ $\ce{Fe[(CO)5]},$ $\ce{[Cr(CO)6]}$ and $\ce{[V(CO)6]-}.$

I thought the $\ce{C=O}$ bond strength would be lowest in $\ce{[V(CO)6]-}$ since the negative charge meant that vanadium had an excess of electrons, hence the metal-carbon back-bonding would be the strongest. As the result, the $\ce{C=O}$ bond order would be the least.
However, the answer given states that iron in $\ce{Fe[(CO)5]}$ has a $\mathrm{3d^8}$ configuration, which means four electron pairs for back-bonding as compared to $\mathrm{3d^6}$ in $\ce{V-},$ hence it would have a greater degree of back-bonding and thus its carbonyl bonding would be the weakest.
Is this correct or does $\ce{[V(CO)6]-}$ have the strongest metal-carbon synergistic bond? If the former is correct, then does a synergistic bond depend on the number of lone pairs first and a negative charge is only considered if the number of lone pairs is the same?


texts:
I'm not very comfortable with chemistry and I need to convert $\ce{CH4}$ concentration values in $\pu{ppm}$ to $\pu{g/m3}$. Is that possible?

I've already researched a bit and realised that for water you can assume $\pu{1 ppm}$ equals $\pu{1 mg/L} = \pu{1 g/m3}$. But since I'm measuring concentrations in the air this might not be correct.

I really appreciate any help. Thanks!


texts: How many valence electrons does the azide ion have?

texts:
We had a test and and we had a question asking the number of valence electrons in an azide ion, $\ce{N3^{-}}$.  I find out that the answer is 16 but I could not understand how.
 I saw the structure. It says that the end nitrogen have a -1 charge and the middle nitrogen has a +1 charge.

From where does the one of the end nitrogen get the electron assuming the other end nitrogen gets it from the middle nitrogen?


texts: What you understand by "Order of reaction"?

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When studying Kinetic chemistry (and most of the Physical chemistry topics), we often find definitions based upon the mathematical formalism. For example, Order of reaction is often defined as the sum of the partial order of a Rate law.
But is there a way to define it without using the mathematical formalism? I mean, if we think microscopically, how would we define Order of reaction?


texts: Phosphate buffer from phosphoric acid and K2HPO4?

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Is it possible to make a solution of ph 7 phosphate buffer solution using phosphoric acid and $\ce{K2HPO4}$ ? How can I calculate the amount of $\ce{K2HPO4}$ needed for 1L of phosphoric acid ?

Edit:
I have 50 mL of 0.2M $\ce{H3PO4}$ solution. How can I convert this solution into 50 mL of pH 7 buffer solution by adding (only) $\ce{K2HPO4}$ ? How can I calculate the weight of $\ce{K2HPO4}$ considering all the equilibria present in the $\ce{H3PO4}$ solution and by the application of Henderson-Hasselbalch equation ?


texts: Can atoms other than hydrogen be reduced to a bare nucleus?

texts: In acid-base theory, hydrogen is able to become the $\ce{H+}$ ion, or a bare proton. I'm curious if other, larger atoms can have their electrons stripped to the point of being only a nucleus. I know helium can in the form of an alpha particle, but are there any other examples? For example, could you have $\ce{Li^3+}$?


texts:
Question
Which is not considered an isomer for pentane?
A) $\ce{CH3CH(CH3)CH2CH3}$
B) $\ce{CH3CH2CH(CH3)CH3}$
C) $\ce{CH3CH2CH2CH2CH3}$
D) $\ce{CH3CH=CHCH2CH3}$

I knew A and B were obviously isomers. I knew D was not an isomer, because the definition of isomers in my book states that isomers "are two DIFFERENT compounds with the SAME molecular formula" and that structural isomers are compounds with SAME molecular formula but DIFFERENT structure.
I was very confused with the choice C since it was IDENTICAL and did not match the definition. What confused me more is that there were practice questions in the book that gave like 4 examples of compounds and asked if  they are isomers or identical compounds.
So, are identical compounds considered isomers or not?


texts: How is Raoult's law a special case of Henry's law and not vice versa?

texts: I know that Raoult's law can be a special case of Henry's law when the value of the Henry's constant becomes equal to the vapour pressure of the pure state of the liquid. Why can't we say the opposite, i.e. Henry's law is a special case of Raoult's law?


texts: Why are alpha carbonyl halides most reactive towards SN2 reactions?

texts:
Relative rates of some compounds towards SN2 is given below

The reason for reactivity of alpha carbonyl  halides is given as

It’s not clear what exactly is happening.


texts: Transition Metals colours and electron absorbtion

texts: I understand that when d-orbitals split some electrons can occupy the higher orbitals by absorbing frequencies of light, but do these electrons then fall back to their original ground states? If so, why? Why don't they remain in a permanently excited state?


texts: Stoichiometry Chemistry Lab: Copper (II) Sulphate Pentahydrate and Iron Single Displacement Reaction?

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In my grade 11 chemistry class, we performed a lab in which we added 1.00g of iron to 6.00g of copper (II) sulphate which was dissolved in water. Using stoichiometry, we predicted that if the iron was ferrous iron, 1.14g of copper would be produced and if the iron was ferric iron, 1.71g of copper would be produced. We waited 24 hours for the copper to dry and then we weighed the copper. The copper had a total mass of 1.24g. We then asked our teacher how this could be as we could not have ended up with more copper than 1.14g (as she already told us that the copper was ferrous). She told us that we need to make sure we rinse the copper really well.

So we decided to do a second trial. We were extra careful in our measurements and we made sure to rinse the copper well with distilled water. We waited 24 hours for the copper to dry and weighed the copper. The copper had a total mass of 1.21g. This was an improvement, but we also understood that we cannot have a percentage yield of over 100%, while ours was 106%.

What could have caused the copper to have a mass larger than predicted? Also, what was the reasoning behind my chemistry teacher advising us to rinse the copper before we let it dry?

Note: I can provide photos and calculations, as well as any other information if it is needed. Thank you!


texts: In the question it mentions that the protein forms dimers. Does that affect the RFM of the protein when I use it in my calculations (10kDa). For example for part a, would it just be. 0.01/10, 000 = 1 x 10^-6 moles. Then divided by the volume which is 0.1 l to find the concentration which would be 1 x 10^-5 M. Thank you


texts: Why are electrons shared equally when calculating formal charge, but unequally when calculating oxidation state?

texts:
When calculating formal charge - electrons are shared equally between
the atoms in the bond.

When calculating oxidation state - electrons are both given to the
most electronegative atom.

Why is this different?

I am assuming it is something to do with the intended use of calculating formal charge and oxidation state, which I believe are:

Formal charge can be used to find the most stable structure.
Oxidation numbers can be used to determine what will become oxidised
in a redox reaction.

However, even based on their uses, I am unsure why they are calculated differently.

*Images from Wikipedia


texts: Which acetate salt is blue and turns yellow when dissolved in water?

texts:
***Update
Some questions I am considering to try to answer this question;

When dissolving the powder in acetic acid, which ions are present?
From what I've read, I haven't found any acetate salts that are not soluble in water. What other metal salts could be forming that aren't soluble?
Which ions might be present in the rock that would not readily react with the acetic acid?
What would be a good compound to replace the acetate ion in a double replacement reaction such that the resulting metal salt would precipitate out of solution?
Are metal acetate salts prone to reaction with oxygen? Are the metal ions in the acetate salt more attracted to the oxygen or the acetate ion? (i.e. will my sample 'rust'?)

I am leaving the main question as-is, posting this update because asking questions is part of my problem solving process.

I was experimenting with the (air) dried residual powder residue left over from cutting this rockin my wet saw in an attempt to determine the composition of the metallic components of the rock I was working with.
The rock appears to be a crystalline silicate rock of some variety. It has minimal to no reactivity with concentrated HCl in its raw form. The geology of the area indicates it was once shallow ocean, with lots of limestone and cryptocrystalline quartz and crustaceous fossils in the surrounding area.
The compound in question was created by soaking the residual powder in 7% white vinegar (acetic acid) for several days with constant stirring. The remaining solution was separated under vacuum filtration and residual solid was again left to air dry for several days. After several days I noticed that the top layer of the filtrate had turned brown with blue splotches. The bottom layer was white with bright blue speckles mixed in.
% isopropyl alcohol I scraped off the top layer and set aside for solubility tests. It was nearly insoluble in  and soluble in water. When the mixture dissolved in water, it turned yellow.
My hypothesis was that the blue compound was copper acetate, the dark brown solution is iron(II) acetate and the yellow in solution is an iron/copper coordination complex. I also suspect there is aluminum in the rock as a USGS survey indicated the presence of muscovite in the region and calcium due to the abundance of fossilized sea shells and limestone. Though I may be completely wrong. I would love if anyone could shed some light on this for me or point me in a different direction for determining the trace elements in the rock.


texts: Effect of pressure on adsorption of a gas

texts:
I am currently studying about the basic terms of surface chemistry, and am facing some conceptual doubt regarding the following:

What effect does pressure have on the adsorption of a gas (adsorbate) on a adsorbent? I don't understand the fact that the adsorption of a gas increases very rapidly as the pressure is increased from small values at low temperature.

I have the idea that increasing the pressure brings the molecules of the gas close together so that they have more intermolecular forces of attraction, but how do I correlate this with adsorption?


texts: Why BH3 its classified as a "Molecular Hydride" and AlH3 its a "Intermediary Hydride"

texts:
First, I understand that, on $\ce{BH3}$, they eletronegativity difference between $\ce{B}$ and $\ce{H}$ is very small. Which mean that the $\ce{B-H}$ bond is less polarized.
But, I couldn't find a relation of this, to the fact that he is a Molecular hydride.
And, secondly, I couldn't understand why $\ce{AlH3}$ its "intermediary", and not molecular, as well...


texts: What exactly are Van der Waals forces? How do they arise and how can an instantaneous dipole cause another dipole? Shouldn't this make a chain reaction that causes all matter to eventually become polar?


texts: What is a good undergraduate bioorganic chemistry book? I would like one of these as I'm tired of non-university books on the subject.


texts: Can we do column chromatography for the purification of metal complexs?

texts:
In case of organic ligands there are several techniques for purification, but in case of metal complex (using $\ce{Cr,Mn,Fe,Co}$ as central metals), I have not seen any literature for the purification of them except recrystallization.

Can we do column chromatography for the purification of metal complexes?


texts:
Why are quantum mechanical calculations so computationally expensive? What exactly is the process that makes it so time taking?

What I mean is, one can perform classical dynamics simulations on a large system like proteins with no difficulty unlike ab initio calculations. Why? What type of calculations are to be performed in ab initio that makes it expensive? Matrix diagonalization?


texts:
After applying sanitizers can they catch fire, if yes, then after what time is it safe to use the hands, say in the kitchen.
Also one more question is that if they are flammable then the flammable component is alcohol. However as soon as we apply the sanitizer the alcohol evaporates? Then how can they remain flammable on our hands?


texts: Mechanistic explanation of salt lowering temperature of ice slush

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As we all know, adding salt to ice water lowers its temperature.

I've read plenty of system-level accounts of energy balances, enthalpies, vapor pressures, phase equilibria and freezing points—I understand that chemists' bread and butter is doing energy arithmetic on thermodynamic systems as a whole, but I would like to gain microscopic-level intuition instead of just being handed some thermodynamic abstractions.

I am looking for an intuitive explanation that details, step by step, at an atomic level, what happens at the interface between the ice and the salt water. For each step, I would like to understand:

What energies (kinetic/temperature vs. latent/chemical) are involved, and where?
How exactly (atomically or subatomically) is one type of energy converted into the other?
Why is each step energetically favourable? Or is it not, and it's reversible? How reversible, statistically?

The explanation should be clear enough that I should be able to intuitively answer the following, without consulting diagrams:

How does the concentration of salt change the evolution of the system (again, at a microscopic level)
How does adding e.g. ethanol instead of salt change things?
Is liquid water required at all? Is salt able to melt and cool completely frozen ice, or is external force required (stirring, driving over it, etc.) to cause some initial melting for anything to happen? (I've read conflicting answers to this in the past.)


texts: Why is the dipole moment of chloromethane larger than the dipole moment of fluoromethane?

texts:
On the Pauling electronegativity scale, fluorine and chlorine are 3.98 and 3.16, respectively.

Since the dipole moment is dependent on electronegativity, why is the dipole moment of chloromethane larger than the dipole moment of fluoromethane?

I guess that the smaller size of the s orbital in the fluorine atom has something to do with this.


texts: How could scientists produce accurate chemical structures before they could capture images of molecules?

texts:
How were scientists able to produce these accurate structural diagrams long before scientists were able to capture images of the actual molecules?

Reference: Scientists capture first images of molecules before and after reaction


texts: What is the hybridization of oxygen in furan?

texts:
I fail to understand why the hybridization of oxygen in furan is $\ce{sp^2}$. I think that since there are 2 bond pairs and two lone pairs so it should be $\ce{sp^3}$ hybridized?

Is it to do with the aromaticity of furan?


texts: How do xanthan gum and other hydrocolloids work?

texts: Does anyone know what causes things like xanthan gum to make water into a slimy substance on the molecular level?


texts: Does the salinity in seawater affect the process of alkaline hydrolysis?

texts: I am an architecture student doing a project on crematorium spaces. I am looking at resomation or alkaline hydrolysis as an alternative method of disposition of a body. From what I gather from research, the funeral parlours offering the resomation service uses 80 gallons/ 300 L of water for each body. I am just wondering if in theory such an enormous amount of water could be replaced with seawater? Or does the salinity or pH of seawater inhibit the process?


texts: Regioselectivity in electrophilic substitution of pyrrole

texts: In the electrophilic aromatic substitution (EAS) of pyrrole, why is the alpha position preferred over the beta position so much?


texts: Can I eat the lemons after I have used them as a battery?

texts:
After completing the lemon battery experiment, can I eat the lemons when I'm done?

More broadly, what will happen to the lemons? What are the chemical reactions, what chemicals might be present/missing after running my lemons as a zinc/copper battery? Would it be poisonous, or just unpleasant?


texts:
I have trouble relating to the mole concept. For example in a question like the following:

  How many moles of $\ce{K}$ are in 1 mole of $\ce{KOH}$?

How is it that in 1 mol of $\ce{KOH}$ there is 1 mol of $\ce{K}$ and x moles of $\ce{OH}$? How is it that 1 mol of $\ce{KOH}$ has 6.02×1023 atoms, and then $\ce{K}$ has 6.02×1023 atoms as well. In addition, $\ce{OH}$ will have 6.02×1023 atoms, but if we add these two it's greater than the original number of atoms in 1 mol of $\ce{KOH}$?


texts: Could reduction of an organic compound by reacting it with sodium dissolved in $\ce{NH3}$ still proceed if a metal such as aluminium were used instead of sodium? I'm not sure about the aluminium amine or amide structure that would be formed.


texts: How many possible nucleotide types can be created?

texts:
In the RNA world hypothesis, it has been argued that RNA is made of 4 nucleotides and it can act as a template to create another copy of itself.
And it's been claimed that we only have 5 nucleotides, 4 of which is used in RNA.
And I also searched and realized that a Nucleotide is made of a phosphate groul, a sugar, and a nitrogenous base.
My question is, in the world of possibilities, how many types of nucleotids can be created? And if it's more than 5, then why nature has only created 5 of them?


texts:
I want to ask a question about chemical potential, $\mu$.
I dislike the use of integrals to describe quantities in thermodynamics. If we observe the definition of chemical potential for constant pressure:
$$\mu_i = \left(\frac{\partial G}{\partial N_i} \right)_{T, P, N_i \neq N_j}$$
which I can understand to mean the change in Gibbs free energy G for a small change caused by the number of molecules of species i.
However, using some high school mathematics, I wondered if the following interpretation was valid.
If we consider that if $N_i = 0$, $G = 0$ and logically if $N_i = N_i$, $G = G_i$, integration by separation of variables will yield:
$$\partial G = \mu_i \times \partial N_i$$
$$\int_{0}^{G_i} \partial G = \mu_i\int_{0}^{N_i}\partial N_i$$
such that
$$G = \mu_i \times N_i$$
and hence
$$\mu_i = \frac{G}{N_i}$$
where the chemical potential of a species $\mu_i$ can better be expressed as the Gibbs free energy of a species $G$ divided by the amount of substance $N_i$.
Is this a more reasonable yet valid understanding of the chemical potential?
EDIT a similar equation is derived in [1].
[1] Chen, L. (2019). Chemical potential and Gibbs free energy. MRS Bulletin, 44(7), 520-523. doi:10.1557/mrs.2019.162


texts: How to filter out magnesium acetate (a soluble salt) quickly and cheaply from water

texts:
I am conducting an experiment that involves reacting a weak acid and a weak base to form water and a salt with this overall equation

$$\ce{Mg(OH)2(s) + 2CH3COOH(l) <=> 2H2O(l) + Mg(CH3COO)2(aq)}$$
Currently, I am trying to filter out the salt to purify the water; however, there are specific restrictions.

The filtration process must be able to:

be done quickly. I can't wait a long time for the water to be distilled
be done at home. This filtration needs to be something that the average person can  could do with household ingredients or ingredients they can buy at a drug store (Assume that the $\ce{Mg(CH3COO)2}$ solution is given to them pre-made)

So far, I have tried to use Gelatin as a clarifying agent, which is typically used to clear beer. However, I couldn't find much info on using gelatin with salt water. Does anyone have any insight about using gelatin as a clarifying agent in this solution? Is there a better way to do such a thing that still meets the requirements?


texts:
Setup: A magnesium electrode dipped in a magnesium sulfate solution and an iron electrode dipped into iron (III) sulfate solution

Am I right in thinking that you need to first identify the redox reactions to determine to determine overall voltage of the cell at standard conditions?

I have identified Mg to be oxidized to Mg(2+) at the anode, but I am not sure which is reduced at the cathode. Would it be the sulfate ions?

If it is indeed the sulfate ions, I have calculated the standard electrode potential to be 2.54 volts (is this correct)?


texts: Kolmogorov backward equations in active biological systems

texts:
I am trying to understand the following equations from a paper by Wang et al. [1,  p. 5 at the SI]:

Michaelis–Menten Representation of the Kinesin Cycle
We assumed that there is a strong coupling between ATP turnover rate of kinesin and kinesin stepping on an MT. Each chemical step in the chemomechanical cycle of kinesin was assumed to be irreversible, except ATP binding and releasing (Fig. 1, step i). Consider the following scheme:
$$\large\ce{0 <->[$k_\mathrm{ATP}\lbrack\ce{S}\rbrack$][$k_\mathrm{-ATP}$] 1 ->[$k_\mathrm{s}$] 2 ->[$k_\mathrm{attach}$] 3 ->[$k_\mathrm{ADP}$] 4 ->[$k_\mathrm{h}$] 5 ->[$k_\mathrm{-P}$] 6}$$
Assume that $F_i(t)$ is the probability for the system to reach state $6$ if, at time $t = 0$, the system is in state $i.$ This function is governed by the backward master equations:
$$\frac{\mathrm{d}F_0(t)}{\mathrm{d}t} = k_\mathrm{ATP}[\ce{S}]F_1(t) - k_\mathrm{ATP}[\ce{S}]F_0(t)\label{eqn:1}\tag{S1}$$

Why does equation \eqref{eqn:1} read as
$$\frac{\mathrm{d}F_0(t)}{\mathrm{d}t} = k_\mathrm{ATP}[\ce{S}]F_1(t) - k_\mathrm{ATP}[\ce{S}]F_0(t)$$
and not
$$\frac{\mathrm{d}F_0(t)}{\mathrm{d}t} = k_\mathrm{-ATP}[\ce{S}]F_1(t) - k_\mathrm{ATP}[\ce{S}]F_0(t)?$$
I would like to change/modulate $S(t)=\cos(t)$ in time and see how it changes the states $F_i(t)$
References
1 Wang, Q.; Diehl, M. R.; Jana, B.; Cheung, M. S.; Kolomeisky, A. B.; Onuchic, J. N. Molecular Origin of the Weak Susceptibility of Kinesin Velocity to Loads and Its Relation to the Collective Behavior of Kinesins. PNAS 2017, 114 (41), E8611–E8617. https://doi.org/10/gdj4h5.


texts: Confusion regarding $\delta$ charge compared with electronegativity

texts:
I heard on a lecture of an online site that, let us say, we have two orbitals (1 and 2). Now, it will be like a spherical cloud. Now, what they say is that

Now, we can notice that for orbital number 1. There is a dark region and a light region (right side). Now, what they say is that the darker region means the electron finding probability is more there. Similarly, for the number 2, electron finging probability is more on left side.
Therefore, we say that 1 develops $\delta +$ charge and 2 develops $\delta -$ charge. Therefore, the two will attract each other.
Now, my teacher on the other hand told it a bit differently:

The more electronegativity means more $\delta -$ charge. But, I have a confusion in it. Between $\ce{H}$ and $\ce{F}$. I have drawn a line. Fluorine has 7 electrons. My teacher says that $\ce{F}$ and $\ce{H}$ share that one electron where $\ce{H}$ has one and fluorine 7th electron. Now, since $\ce{F}$ is more electronegative. The electron (by hydrogen) is more pushed towards fluorine. My confusion is that if $\ce{F}$ is more electronegative than $\ce{H}$. Then, the electron should be present more towards the $\ce{H}$ side.


texts: Is there a shortcut method to calculate the Steric Number?

texts:
The steric number is equal to the number of $\sigma$-bonds + the number of lone pairs of electrons on the central atom. It gives us the number of hybridised orbitals.

It is pretty straight-forward to calculate it, but the problem here is that one must always draw the Lewis Structure before one can actually get to calculating the steric number, and then the number and types of hybrid orbitals. Even that is quite simple for a smaller compound, even like XeF$_6$, but when it comes to complex hydrocarbons, it's a little difficult.

My question is that is there any well-known (or not so well-known, but working) shortcut to doing this, so as to save time? It would be great if anyone could share their ideas and help me out.

Thanks in advance.


texts: Proper IUPAC name of a substituted cyclohexenol

texts:
Here's the molecule:

So far I've tried: 6-methylcyclohex-2-en-ol and 4-methylcyclohexen-3-ol but both are wrong. I'm rather confused as to where I should start: the alcohol or the double bond?


texts:
I was doing a reaxys substructure search for the compound shown on the left below, with the 3 amines on 1 carbon. However, the closest I found were all trinitro compounds like on the right. I would have thought the nitro compounds would be less stable and likely to explode. But given the lack of triamine compounds, they must be hard to make. All I can figure is that when all three amines are protonated you end up packing a lot of postive charge in a small place.

Now that I look at that nitro structure I'm pretty sure I got the charges wrong. Just ignore that.


texts: Number of hyperconjugating structures due to a C=N system

texts:
How many hyperconjugating strutures are there for the following compound?

I thought the answer to be 8 (as there are eight alpha hydrogens) but the correct answer given is zero. Why isn't the answer eight here, as expected from a $\ce{C=C}$ alkene? Does the explanation invoke the very definition of hyperconjugation?


texts: Sodium metal burning off when conducting electrolysis and I don't know why

texts:
I melted down some table salt and used high voltage welder power source to try and separate the sodium and chlorine it was partially successful because I could smell and see chlorine gas but during the reaction what I think was sodium would float to the top of the molten salt and burst into flame. Is there a way to prevent this?

I was thinking maybe an airtight crucible, switching the anode and cathode or keeping a lower temperature to prevent it vaporizing. Any answer would be very helpful.


texts: Intensive properties clarification - Chemical thermodynamics

texts:
I just started learning chemical thermodynamics and have come upon the definitions for extensive and intensive properties. I had a great deal of confusion over the exact meaning of intensive properties, but I believe I have come to a proper understanding of it after doing some extra reading. I will present my understanding below, and I just need to clarify that this is exactly what intensive properties are.

Intensive properties are defined differently for homogeneous and heterogeneous systems. For homogeneous systems, intensive properties are those properties that possess the same value at different points within the system and for the system as a whole. For heterogeneous systems, it no longer has anything to do with the value of the property for the system as a whole, but instead transforms into a local property, concerning only small volume elements within the system.
Is this correct, or is there some brushing up needed? As of now I am only concerned with the most general understanding of intensive properties. Hope you could shed some light on this. Thank you.


texts: What causes transition from smoldering combustion to flame combustion?

texts:
What causes the transition from smoldering combustion to flame combustion?

From what I have read about it is that, smoldering combustion gives off a lot of flammable gases, primarily, Carbon Monoxide, however, the lower flammability of carbon monoxide is 12.5% and it takes about 2-3 hours to reach a concentration of 1%, it is lethal to humans in concentration of 1%.

There have been reported experiment studies, where smoldering combustion transitioned into flame combustion, as quickly as 22 minutes. So, there must be some other cause. Carbon Monoxide is, I guess not the reason.


texts: Is a 2-D periodic structure isomorphic with the surface of a torus, a sphere, neither or both?

texts:
When I was reading through the ADF-BAND tutorials, one of the toy systems presented was a 1-D periodic structure involving 3 collinear hydrogen atoms. The tutorial pointed out that, topologically speaking, this is cylindrically symmetrical (more specifically, it's ring symmetrical).

In the instance of a 2-D structure, can the calculation be considered a model for the surface of a torus (this seems logical), a sphere (I doubt this because if you fit a rectilinear grid to a sphere you end up with two poles and dissimilar meridians and parallels), or other?

Bonus questions: Has anyone used periodic calculations to model electronic structure/chemistry on the surface of a sphere or torus? Can you introduce a curvature term to account for these structures having a finite size?


texts: On the notion of a component in thermodynamics

texts:
Wikipedia article on a component (in thermodynamics) first mentions that:

  In thermodynamics, a component is a chemically-independent constituent
  of a system. The number of components represents the minimum number of
  independent species necessary to define the composition of all phases
  of the system.

A bit later it is said in the same article that:

  The number of components is equal to the number of distinct chemical
  species (constituents), minus the number of chemical reactions between
  them, minus the number of any constraints (like charge neutrality or
  balance of molar quantities).

How does the second statement follows from the first one?


texts: What are similarities and differences among shells, orbitals, subshells, and energy levels?

texts:
I think I know what these terms mean:

each row on the periodic table has a new shell of electrons,
a subshell is e.g. 1s, 2s, 2p, 3s, 3p, etc.,
and energy levels are the same as shells,
whilst orbitals are the same as subshells.

Is this correct or totally wrong?


texts: Should chemical compounds and elements be capitalized?

texts:
In the case of a name of a person, the first letter is written in capital letters.

Should the first letter of name of a chemical compound or element be written in capital letters?


texts:
Why is the following compound called "1,1,1-trifluoro-2-chloro-2-bromoethane"?

Why is this not called "1-bromo-1-chloro-2,2,2,trifluoroethane" alphabetically? (the name, 1,1,1-trifluoro-2-chloro-2-bromoethane was in my CGP A level chemistry textbook :))


texts:
What’s the name of the following compound?

$$\ce{CH3C(p-ClC6H4)2CH(Br)CH3}$$

My teacher said that she strongly thinks( with another teacher) that it should be 3-bromo-2,2-bis-(4-chlorophenyl)butane, though many other books and other students (similar to me) stated that it should be 2-bromo-3,3-bis-(4-chlorophenyl)butane.

She asked us try to find it out. Any organic chemistry experts out there?


texts: Why are we not supposed to heat Erlenmyer flasks?

texts:
Chemistry says that we are are we supposed to heat boiling flasks, and not Erlenmeyer flasks.  However, I can't find any information about this on Google.  Is there a particular reason for this?

Is it just because we want to separate the purposes for our glassware, or is there an actual valid reason?


texts: Diastereotopic methylene protons in achiral molecules

texts:
Are the protons in methylene groups of achiral molecules such as propane-1,2,3-triol or 3-hydroxypentanedioic acid diastereotopic?
Consider propane-1,2,3-triol. To me, replacing one of the protons in either -CH2 with an arbitrary X nuclei creates (what I work out as) 2 diastereomers. However, NMR simulations of propane-1,2,3-triol in ChemDraw and on nmrdb.org (https://www.nmrdb.org/new_predictor/) do not flag these hyrdogens as diastereotopic and neither does this "Diastereotopic atoms" computational tool (http://www.cheminfo.org/Spectra/NMR/Tools/Diastereotopic_atoms/index.html).
I have also played around with physical models of each isomer and cannot find a plane of symmetry to make them enantiomers.
What am I missing here?


texts: Does PO3- exist as a free ion or in a cyclic/linear polymeric form?

texts:
My book says that $\ce{PO3-}$ exists as cyclic or linear polymeric structure but doesn't elaborate on this. I Googled this and found no result either.

Also, what would be the structure of $\ce{PO3-}$ cyclic or linear polymeric structure.


texts: How to determine polarity in large molecules?

texts: In case of small molecules like water things are more or less clear, but when I see a large complex molecule like Thyroid Hormone - how should I find out that this molecule is non-polar?


texts: First usage of PEG (Poly ethylene glycol) on surfaces against biofouling

texts:
Is there something like a "famous initial case" when people used Poly Ethylene Glycol (Poly Ethylene Oxide, PEG) as passivating layer or so on surfaces? Especially against nonspecific Protein or Peptide binding?

I found one publication from 1971: "Treatment of controlled pore glass with poly(ethylene oxide) to prevent adsorption of rabies virus" (Hiatt et al), however this has been cited only very rarely.

On the other hand there is the famous precipitation method described by Polson et al from 1964.


texts: I have a 55 gallon drum half ful of liquid. I would like to put a "blanket" of nitrogen over the liquid. How can I replace the air in the drum with nitrogen?


texts: How easy it is for MoS2 to become oxidized

texts:
I made I high pressurized $\ce{MoS2}$ pellet, using a 6 ton pressurizer. I used very thin powder to create the pellet.

I am using this pellet on beam, with some nuclear techniques. In my spectra I can see oxygen.

How easy it is for $\ce{MoS2}$ to become oxidized?


texts: What happens to iron(III) sulfate (ferric sulfate) in aqueous solution?

texts:
Iron(II) sulfate (ferrous sulfate) is a salt that, in an aqueous solution, dissolves and yields $\ce{Fe^{2+}(aq)}$ and $\ce{SO4^{2-}(aq)}$. It then decomposes to ferric sulfate shortly thereafter.

But what happens to the iron(III) sulfate (ferric sulfate) in solution? Is the $\ce{Fe_2(SO_4)_3}$ compound preserved?


texts: Possible mechanism by which a methyl glycinate hydrochloride salt in toluene (insoluble) reacts with an acid chloride through the nitrogen atom?

texts:
I'm trying to work out a possible mechanism for the reaction of a methyl glycinate hydrochloride salt in toluene (it is insoluble) with an acid chloride, reacting through the N-terminus. As the amine is protonated (hydrochloride salt), it is non-nucleophilic and insoluble in the toluene. The question states that upon addition of the acid chloride and heating under reflux for 4 hrs the insoluble salt slowly goes into solution.
Given the salt is non-nucleophilic, I am struggling to see a way that the reaction could take place. My current thoughts are that a small amount of the salt must exist in the non-polarised form (an amine + HCl) and this is what reacts as the amine is a nucleophile and so able to react with the acid chloride, forming a soluble product hence the gradual dissolving over time.
Would this be correct, or am I missing something? Any suggestions much appreciated!
Edit: There is no base such as Et3N in the solution, although I imagine that could solve the problem quite nicely!


texts:
I saw the MO diagram for a NH3 molecule but couldn't understand why the combined atomic orbitals were in the positions they were, and if these positions were fixed.

Why is the sigma anti bonding lower in energy than the pi anti-bonding? Is it something you have to learn off by heart for each common molecule?


texts: Deprotection (debenzoylation) of glucose (sacharide) using NaOMe leads to hydrolysis glucose

texts:
I have a problem removing the benzoyl groups of my glucose moiety using sodium methylate (standard procedure). Indeed, the benzoyl groups are removed. However, a significant amount of glucose gets hydrolysed leaving an alcohol group. I have tried different equivalents of sodium methylate and also other bases like potassium carbonate and ammonia. However, in all cases hydrolysis takes place.

Does anyone have an idea why hydrolysis takes place? Could it have something to do with the TMSOTf (strong acid) in the previous step? The only workup I did for compound 1 was quenching the reaction using the same molar amount of TEA as TMSOTf, then evaporating $\ce{CHCl3}$, then silica column chromatography ($\ce{CHCl3 : MeOH}$ in $10 : 1$, see picture). Is it possible that TMSOTf is still present in my compound?

Column of compound 1:


texts: What is the origin of chirality in the universe?

texts: I am just curious with the fact that our body is made of so many chiral molecules the DNA that we possess is chiral, the amino acids in our body is chiral and there are many other objects other than the molecules which show chirality. So,I want to know what is the origin of chirality in the universe.


texts: Does diamond have a pungent smell like graphite?

texts: I was writing down a chemical equation with my pencil and noticed the pungent smell of the graphite. This made me wonder if other substances made of carbon, such as diamond, have a similar pungent smell?


texts: Why does iron have an abnormally high ionization energy?

texts:
Along a period the ionization energy should increase because the atomic number is increasing, but there is negligible increase in shielding. However, $\mathrm{IE}_\ce{Mn} < \mathrm{IE}_\ce{Fe} > \mathrm{IE}_\ce{Co} > \mathrm{IE}_\ce{Cu}$, so why does iron have such a high ionization energy?

I've considered that iron has a $\mathrm{4s^2 3d^6}$ configuration that goes to a $\mathrm{4s^1 3d^6}$ configuration upon ionization, while $\ce{Co}$ has a $\mathrm{4s^2 3d^7}$ that goes to $\mathrm{4s^0 3d^8}$ configuration, $\ce{Ni}$ has a $\mathrm{4s^2 3d^8}$ that goes to a $\mathrm{4s^0 3d^9}$ configuration and $\ce{Cu}$ has a $\mathrm{4s^2 3d^9}$ that goes to a $\mathrm{4s^0 3d^{10}}$ configuration (Lang, J. Chem. Ed., 2003).  In the Long paper, the authors explain the increase of IE at iron is due to "electronic structure" and I would like to know exactly what about the electronic structure it is that causes iron to have a high IE than expected based on a general periodic trend.

I was thinking that adding an electron to the $\mathrm{3d}$ orbitals might be energetically favorable enough to lower the ionization energy of $\ce{Ni}$, $\ce{Co}$ and $\ce{Cu}$, so rather than iron having a high ionization energy the surround metals just have a low ionization energy because the ion is stabilized by having another $\mathrm{d}$-electron added? Does that sound reasonable?

Another thing I was thinking was that iron is the first transition metal to have a paired $\mathrm{d}$-electron, could that effect the shielding and increase the ionization energy?


texts:
Recently, a group of researchers from the Nanyang Technological University in Singapore have investigated the novel $\ce {S_N2X}$ mechanism which involves a "frontside attack" on the substrate, rather than the usual "backside attack"$^1$. This may seem peculiar at first. However, the fact that there is favourable halogen bond formation between the electrophilic halogen atom and the incoming nucleophile certainly does help to explain why this unusual "frontside attack" would occur.

There are quite a few other similarly peculiar reactions in organic chemistry in which the nucleophilic species first attacks a halogen atom. These include the Appel reaction and the Corey-Fuchs reaction. I was wondering if the formation of an intially halogen-bonded complex the reason why these reactions can proceed.

Reference

Zhang, X.; Ren, J.; Tan, S. M.; Tan, D.; Lee, R.; Tan, C.-H. An enantioconvergent halogenophilic nucleophilic substitution ($\ce {S_N2X}$) reaction.  Science 2019, 363, 400-404.


texts: Calculation of average bond length from force constant and IR absorption?

texts:
I need some help beginning a problem set problem (just want hints, I'd like to figure it out myself).

The problem gives me the IR absorption for a diatomic, as well as the force constant for the bond. It asks me to identify the the average separation (bond length) of the two atoms.

I am stuck because the typical Schrodinger equation for harmonic oscillation takes "displacement from equilibrium length" as its variable: $\hat{H}\psi_{v}(x)=E_{v}\psi_{v}(x)$. A change of variables such as $x = l-l_{0}$ would require I know the average separation, which I am trying to solve for.

Any help or direction to relevant resources is greatly appreciated.


texts: How much muriatic acid to dissolve cinder block?

texts:
Can a cinder block be dissolved in hydrochloric (muriatic acid) ?

Also if it can then how much hydrochloric acid will be needed ?


texts: What's the source of electrical energy in galvanic cells?

texts:
Let's take a simple Daniell cell for example:

Where does the energy required to drive electrons through the external circuit and power up devices (like a light bulb) come from? Does the oxidation of zinc release that energy? And, does the reduction of copper result in more energy being released? (since we're calculating the cell potential by adding up the oxidation and reduction potentials of the two half cells). I've always wondered about this question, and I'd really appreciate a clear and concise explanation regarding this particular topic.


texts: What are the factors affecting Boiling Point in Ions?

texts:
I understand that for molecular substances, intermolecular forces such as van der Waals forces and hydrogen bonding are the major factors effecting the boiling point.

However, I am not sure about what factors effect the boiling point in Ionic substances.  I assume it is to do with the strength of the bonds between ionic units, but then what effects this strength?

Thanks for your time!


texts: How to minimise solution concentration changes due to evaporation?

texts: Lets say I have a precise solution, and would like to store it long term (up to two years) with as little as possible change in concentration. The volume is 10-100ml. What container should I choose? What temperature? Is there any other factors? I would prefer not to use sealed glass container. Is there a way to approximate a solvent loss?  What if I stored some water in exactly the same conditions together with my sample, would I be able to approximate water loss in my sample from the water loss in this reference container, or does the difference in the concentration of the solute affect the rate of evaporation too much?


texts: Periodically oscillating chemical reactions?

texts:
I've seen before chemistry demonstrations where solutions are mixed with one another and subsequently where the resulting product goes through periodic color changes: for example blue to orange and back to blue again. The reaction seems to go on for awhile at a regular period.

My question - can this reaction be considered resonance in the sense that energy is flowing back and forth between two chemical states? In such reactions are there actually two chemical species between the color changes or just energy level/temperature differences?


texts: Enantioselective organic reaction not working

texts:
I'm performing the reaction between acetone and 2-nitrobenzaldehyde catalysed by (L)-Proline, as answered to one of my questions a while ago: Simple experiments involving enantiomer synthesis

However, while the literature specified using 1 mmol of (L)-Proline in 20ml of solution, due to the cost of the materials and the budget available, I've only been able to use a fraction of that, around 0.01mmol. I've scaled down the entire experiment to 5 ml to try and compensate for this.

The issue is, I've left this solution reacting for a long period of time (12+ hours) and I'm not seeing any optical activity at all. With the reduced concentrations, I'd have expected to see a lot less activity than the original literature specifies, but to see at least some indication that my reaction is working.

Are the concentrations of (L)-Proline simply too small for any significant reaction to take place? Or can there be some other reason why my reaction isn't working? Note: I'm a chemistry 'newbie', so don't assume anything!


texts: Is it true that heavy water is not blue?

texts:
I believe I saw this claim somewhere on the internet a long time ago. Specifically, it was claimed that the difference could be observed by filling one long, straight tube with light water and one with heavy water, and looking through both tubes lengthwise (so that light has to travel through the tubes' lengths before reaching the eye), whereupon the light water would appear blue as it does in the oceans, and the heavy water would not. The explanation given was that heavy water has a different vibrational spectrum because of the greater mass of the $^2$H atom, which seemed perfectly plausible.

However, I am no longer able to find a source for this claim, which is strange because if it were true, surely it would not be so difficult to find a source?


texts: For a chemistry lab, I'm required to calculate the vapor pressure of some organic solvents... methanol, ethanol, and propanol, in addition to an "unknown" sample of some solvent. In the lab, we were instructed to heat these solvents in a sealed syringe along with 5 mL of air. While they were being heated, I recorded the volume and temperature of the air and solvent in the syringe. Now, from that data, I need to calculate the vapor pressure of these substances at the temperatures at which I recorded the data. How can I do this?


texts:
Stock solution 0.1M KI solution 100mL

Volume of KI
30
10.5
5.25

Volume of water
0
19.5
14.75

concentration of KI
0.1
0.05
0.025

How did they calculate these numbers?
 I tried c1 v1 = c2 v2
For example for 0.05M:
(0.1)(v1) = (0.05)(30/1000)
v1= 0.015L = 15mL, what does this 15mL represent. How did they calculate the volume of KI and water.

I want to dilute KI and I want the final solution to be 30mL. And the concentrations that I need are shown above (0.1, 0.05, 0.025, 0.0125).

Please help


texts: What is the approximate cost per unit length to synthesize carbon nanotubes free of defects?

texts: As implied near the end of this article, carbon nanotube fibers have been synthesized in chunks on the order of about a centimeter in length (Fei Wei at Tsinghua University in 2018). What is the cost per unit length for making these fibers? Does it seem feasible to do so in the next 5 years, 10 years, 20 years?


texts: How to measure the amount of calcium in a supplement?

texts: In chemistry lab, my group was assigned to determine the actual amount of calcium in a supplement.  We did this successfully using HCl to dissolve the tablet, vacuum filtration, and then the addition of sodium carbonate.  Next week, it has been suggested that we attempt it again using a different method.  Thus, we are seeking the most interesting way, albeit using elementary tools and chemicals, that one might do this.


texts: 2,2,6,6-Tetramethylpiperidine - Brønsted Basicity

texts:
I understand that this molecule can only act as a Brønsted base because it is sterically hindered by its multiple methyl groups.

However, isn't the proton bound up in solution? Doesn't that increase the effective size of the proton? How then exactly is a proton expected to reach the site of basicity if it's tied up with multiple water molecules? Or is the size of the hydrated proton still quite small? Or does the proton separate from the water molecules once the proton is sufficiently close to the site of basicity (the lone pair on the nitrogen)?


texts:
Let me premise this with the fact that I really have zero knowledge of chemistry. So bear with me and my ignorance.  :)

Now, with that introduction out of the way, I've read up this site which presented in a very easy to understand way, how a Nitrogen atom bonds to yet another Nitrogen atom to make a fairly common element $\ce{N2}$.

Continuing, it says on that site that when you create $\ce{N2}$ from two Nitrogen atoms, that's as far as you can go for creating covalent bonds between Nitrogen atoms.

Armed with that knowledge, my question is as follows:

- Can you create further bonds utilizing another atom and still keep the strength of a triple bond and $\ce{N2}$'s natural inertness?


texts: Are electron orbital orientations filled in any particular order?

texts: This question is about the magnetic quantum numbers and their corresponding orbital orientations, e.g., px, dyz, etc. Are the electrons in any given subshell distributed across the orbitals in any particular order as the number of electrons increases?  Such as m = -1 first, then m = 1, etc.?


texts: Why do we get slightly more inversion product than retention product in SN1 reaction?

texts:
Theoretically, in $\mathrm{S_N1}$ reaction we should get a racemic mixture as the product because the nucleophile can attack from either side of the formed carbocation.

However, many textbooks claim that there's slightly more inversion product than retention product.

Is there any specific reason for this to happen.


texts: Two-electron Integrals over Gaussian Plane Waves

texts:
Is there an efficient method to compute the two-electron integrals over the basis set represented by a product of a Gaussian function $g(r)$ and plane wave:

$\psi(r)=g(r)e^{ikr}$

where $\lambda=1/k$ is approximately one fifth of the width of gaussians.


texts: What is the difference between electric current and electric charge?

texts:
Are electric current and electric charge the same thing? I'm just getting back into relearning chemistry, so a more in-depth answer about how electricity works in general would be wonderful.

Edit: Thank you all for clarifying that this belongs to the Physics SE. That being said, I guess this question doesn't have much relevance to me anymore. I'm honestly not sure if I should delete the question or not, so I'll leave that up to the mods to decide. Thanks again.


texts: How to convert an oxirane to an alkanol with one additional carbon atom?

texts:
This is a question given in our exam.
In the reaction,

Find the reagents X and Y required for steps(ii) and (iii) are _______ and ________ respectively.
I have tried in this way but I have stuck in second step. The given compound reacts with PhCO3H to form an epoxide.
Am i correct? Then please help me continue the reaction.
The answer given is CH3MgBr and H3O+.


texts:
There are amphiprotic (or amphoteric) substances, like $\ce{H2O}$ and $\ce {HCO3-}$, which act both as an acid and base.

If you mix a strong acid like $\ce{HCl}$ ($\mathrm{p}K_{\mathrm{a}} = -6.3$) with an even stronger acid, such as perchloric acid ($\ce{HClO4},~\mathrm{p}K_{\mathrm{a}} \approx -10 $) can it act as a base?


texts:
I will be doing a lab on Hydrogen Phosphate buffer system tomorrow and I have a few questions about the buffer system. I am not sure if my assumptions are correct.

(1) What would happen to the rate of pH change if 5.0M HCl and NaOH were used instead of 0.50M?

My assumption is that, since the pH of the buffer does not depend on the actual concentration of the buffer, but on the ratio of the two parts, therefore, the rate of pH should not expect to change. Is this correct?

(2) Lets say I prepared a buffer at a different pH, how would the capacity of my buffer system change?

My assumption is that, the buffer capacity would not change upon the change of pH, is this correct?


texts: Optical activity of cis coordination compounds

texts:
I came across a statement saying,

  "Consider a Octahedral coordination compound of type [MA2X2]. Then,
  if the compound is in a cis form, it shows optical activity as there
  is no plane of symmetry and hence is non-superimposable on its mirror
  image. On the other hand, a trans form is symmetric and superimposable
  on its mirror image and so is optically inactive."

I do not see why the cis form is not superimposable on its mirror image. If all the ligands lie on the same plane, then isn't there a line of symmetry passing diagonally? Does that not make it superimposable on its mirror image?


texts:
Today, I made a cup of lemon tea in a different way than usual. Instead of pouring hot water in to a mug containing lemon juice and black tea (my normal routine), I let the tea steep for a little while before squeezing the lemon. Before adding the lemon, I noticed that the tea was much darker than I am used to. After squeezing the lemon, the tea changed color to a lighter brown and became more translucent.

I could see only a half inch down the side of the cup before squeezing the lemon, but afterwards I could see three inches down, all the way to the bottom. I did not notice any precipitated solids on the bottom of the cup. What happened?


texts:
My attempt to the question:
We know that more polar the $\ce{O-H}$ bond, the more acidic is the compound. According to electronegativity, the $\ce{O-H}$ bond of $\ce{HOF}$ should be more polar than $\ce{O-H}$ bond of $\ce{HOCl}$ since electronegativity order is $\ce{F} > \ce{Cl}$. But we should not miss another factor! That is the backbonding of  2p electrons (lone pairs) of oxygen with the 3d vacant orbital of chlorine. This is not possible in $\ce{HOF}$ due to the absence of vacant orbitals. Backbonding reduces (maybe, I do not know) electron density in oxygen and therefore polarity of $\ce{O-H}$ bond increases.


texts: Crystal Field Theory - Operator Equivalent Methods

texts:
I am a bit confused by some of the points of operator equivalent methods in crystal field theory. I would appreciate any help I could get with any of my questions.

First, I am confused as to the difference in the operator equivalent method for the single electron case and the multiple electron case. I have read, for example, in Hutchings 1964 and Bleaney & Stevens 1953 that one considers $\mathcal{H}=\sum_{n,m}B_n^mO_n^m(L)$ where $L=\sum \ell_z$. However, this confuses me because for example, in $(3d)^7$, by Hund's rules, $L=3$. Therefore, in this operator equivalent method, one would expect a splitting into two triplets and singlet state. However, the d orbital has $\ell=2$, so one should have a five dimensional representation which splits into a doublet and triplet by group theory (as in Dresselhaus or many others). Indeed, I have seen conflicting diagrams from different sources. For example, in Section 6.2 here, it has $\ce{Co^{2+}}$ splitting from seven levels. However, in this paper, $\ce{Co^{2+}}$ splits from five levels, which makes sense to me because even if $L=3$ it is still the $d$ orbital. I think it may be that I'm not understanding what the levels mean in the operator equivalent method, but I'm not sure where to look.

Second, even if one determines the Hamiltonian using operator equivalent methods, I am not sure how to make good use of it. The operators tend to be written as some complicated function of $J$ and $J_z$ for rare earths (or $L$ and $L_z$ for the iron group), so I'm not sure how to do calculations familiar from more basic quantum mechanics, like finding expectation values of angular momentum or energies.


texts: Order of increasing boiling point is p-nitrophenol > m-nitrophenol > o-nitrophenol. The difference between bp of p- and o-nitrophenol is that one form intermolecular hydrogen bonding while other form intramolecular hydrogen bonding. Then what is the reason for high bp of p- than m-nitrophenol as both form intermolecular hydrogen bonding?


texts: HOMO and LUMOs of Carbon based Compounds

texts: Why are the HOMO and LUMOs often $\pi$ orbitals in carbon based compounds that contain multiple double bonds or conjugation such as ethene and butadiene?


texts: What are the ideal pair of (everyday) elements to pair in a thermocouple

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I want to create a thermocouple (to carry out experiments on thermoelectricity).

I want to use the pair of everyday* elements (e.g $\ce{CuO}$ and $\ce{Al}$ wires) to create the thermocouple. The temperature range of the heat source will be between 300° C - 500° C

My (little remaining) knowledge of physical chemistry informs me that the periodic table would provide useful clues as to which elements to use (that's why I posted this question here, rather than in physics or engineering) - but unfortunately, it's not clear to me how I may use the periodic table in this case, to select the two elements that meet my twin requirements of:

Maximum voltage and current generated (via the Seebeck Effect) within the operating temperature indicated above
Both elements are "everyday" elements

Note: By everyday elements, I mean elements that I can buy off the shelf (preferably, in wire or sheet form), and are relatively inexpensive.


texts: Bond length comparison between two carbon atoms

texts: Why is the bond length of double and triple bonds between two carbon atoms shorter than the single bond length between two carbon atoms?


texts: Chemical Equilibrium - Le Chatelier's Principle, Change in Volume

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Question: Consider the following reaction at equilibrium at a total pressure that we will call $P_1$.

  $$\ce{2 SO2(g) + O2(g) <=> 2 SO3(g)}$$

  Suppose the volume of the system is compressed to $\frac 12$ its initial volume and then equilibrium is reestablished. The new equilibrium total pressure will be:

  a. Twice $P_1$

  b. Three times $P_1$

  c. 3.5 times $P_1$

  d. less than twice $P_1$

  e. unchanged

My thought process: Since I knew the volume had decreased, that meant the pressure had increased and so the reaction will head towards the side with less moles, which would be the products. I thought that since the volume halved, that meant the pressure should increase two times.

However, the answer is D. Could someone please explain this to me?


texts: I'm poaching some pears.  The recipe calls for bringing the liquid to a boil and adding the pears, then simmering until done, about 25 minutes.  It then calls for removing the pears from the liquid and letting both come to room temperature, then putting the liquid over the pears again and marinating overnight.  Separating the pears and the liquid will let the pears cool more quickly and presumably prevent overcooking.  I have heard a rule of thumb that every 10C in temperature doubles the reaction rate.  As the pears simmered for 25 minutes, it seems that the cooldown (even if they stayed in the liquid) will not add much to the reactions of cooking. Is there any sense to extracting the pears from the liquid?


texts: While filling electrons, we follow Aufbau principle, but not while removing them. Why is this so?

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I recently came across a question Why is the vanadium(3+) ion paramagnetic?, where the asker is wondering how $\ce{V^{3+}}$ is paramagnetic (he used Aufbau in reverse to remove the electrons), while the correct answerer to that question remarked that removing electrons must follow the order from outer shell to inner shell. For example, in the case of $\ce{V^{3+}}$ the electronic configuration of $\ce{V}$ is $\ce{[Ar] 3d^3 4s^2}$. The asker used reverse-Aufbau, which is $\ce{[Ar] 3d^0 4s^2}$; while the actuality was $\ce{[Ar] 3d^2 4s^0}$.

My question: Why does filling electrons follow a certain rule, while removing them follows a different rule?


texts: Role of Lewis acid in synthesis of adamantane from bicyclic species

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What is the role of $\ce{AlCl3}$ in the following synthesis of adamantane? I'm guessing it functions as a Lewis acid, but I am unsure how the mechanism of the second step works, as there is no region of high electron density in the bicyclic species.

If a mechanism for the second step exists, I would greatly appreciate if someone could propose one.

Image source: Wikipedia


texts: Using CIP rules in a bicyclic compound with carbonyl subsituent

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In bicyclo[2.2.1]heptan-2-one, arrange the numbered groups according to CIP rules:

Group 1 will have highest priority because oxygen atom is attached to 1. (It can be considered as two oxygen atoms).

Group 4 will have least priority due to least atomic number among the numbered groups.

But I am confused about order of priority of group 2 and 3. Both have same atoms. (So I will check the next atom which is also same.)


texts: Why do many pharmaceuticals contain fluorine?

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What exactly does fluorination of some compound do in a biological sense?

I read the following things about what fluorine does for drugs:

Fluorine withdraws electron density and can make an acid stronger.
Fluorine substitution can increase lipophilicity - I don't understand this. Lipids are non-polar; I can't see why adding fluorine would generally decrease the polarity of some molecule ...
Carbon-fluorine bonds are exceptionally stable and resist change.

However, can anyone provide some concrete examples of fluorine influencing the behavior of some drug? I could only find very general points on the internet.


texts: How do i detect the compounds a plant is made of, automatically?

texts: Let's  say I want to take a random plant , and get the chemical formulas of  the compounds he's made of. Is there an automated method for doing so  and how costly is it(roughly) ?