texts: Oxalate ion dentiticity - why is it bidentate and not tetradentate?

texts: Why is the oxalate ion a bidentate ligand? Why does it not act like a tetradentate ligand (having four oxygen atoms, with lone pairs)?


texts:
The $\mathrm{p}K_\mathrm{a}$ of $\ce{NH3}$ is $38$. Does it stand for the following equilibrium:

$$\ce{NH4+ <=> NH3 + H+} \tag{1}$$ With $K_\mathrm{a} = 10^{-38}$ for reaction $(1)$, indicating that the conjugate acid of $\ce{NH3}$ is quite weak?

The $\mathrm{p}K_\mathrm{b}$ of $\ce{NH3}$ is $4.74$. Does it stand for the following equilibrium:

$$\ce{NH3 + H2O <=> NH4+ + OH-} \tag{2}$$ With $K_\mathrm{b} = 10^{-4.74}$ for reaction $(1)$, indicating that $\ce{NH3}$ is a weak base?

Also: $$\mathrm{p}K_\mathrm{a} + \mathrm{p}K_\mathrm{b} = 42.74 \neq 14$$


texts: Molecular Imaging - Any surprises to be had?

texts:
Molecular imaging, using STM and AFM technologies, appear so far to visually prove most of what we already know about chemical structures, such as VSEPR theory. For instance, here are the ideal structures and AFM of a couple of cyclization reactions:

We've also taken single-atom imaging to pretty scary levels. Behold a field emission electron microscope image of the s and p orbitals of carbon, long relegated to conceptual mathematical images in textbooks:

The question is, have there been any surprises to be had from these images, where something we thought was structured one way was in fact radically different? You can see in the AFM image that some of the bond angles deviate from the ideal regular shapes a little, and it may also be that the electrons in the pi bonds, instead of being regularly distributed, seem to prefer the "far" end of the phenyl rings, but the predicted structures are uncannily accurate. Again, with the orbital imaging, the s orbital isn't perfectly spherical and we don't see the full p-orbital shell, just two "lobes", but again, they're powerful evidence that our theories are right so far.

Has this ever not been the case? Have any of these recent images turned chemistry on its head by showing something totally unexpected?


texts: Why does acetylene, having an acidic proton, not react with strong bases like NaOH and KOH?

texts:
In acetylene (ethyne, HC≡CH), the carbons are sp-hybridised, which make the attached protons more acidic than those in alkenes or alkanes. (See also: Relative acidities of alkanes, alkenes, and alkynes)

Why doesn't acetylene react with strong bases like NaOH or KOH?


texts: Jahn Teller distortion and magnetic moments.

texts:
It is relatively well known that the discrepancy between the observed and experimental magnetic moments in the first row transition metals is attributed to spin-orbit coupling when it comes to metal ions with $A_2$ and $E$ ground states. For example, Cu(II) has an $E_{2g}$ ground state term has the observed moment is slightly higher (1.96 BM for a phenanthroline complex) than the theoretically predicted "spin only" value (~1.73 BM, attributed to 1 unpaired electron). I also know that this is calculated by a formula which makes use of the spin-orbit coupling coefficient:

$μ_{eff}$ = $μ_{s.o.}$(1-$α λ$ /$Δ_o$)

where, $α$ takes up the values 2 (for E ground state) and 4 (for $A_2$ ground state), $\lambda$ is the spin orbit coupling coefficient, $Δ_o$ is the crystal field splitting energy.

My question relates to the possible effect of a Jahn Teller distortion on the magnetic moment of, say, Cu(II). Intuitively, a distortion should reduce the orbital contribution to angular momentum by the loss of orbital degeneracy. On the other hand, for Cu(II), for example, the $e_g$ set is magnetically non active. So does splitting basically have no effect on the orbital part of the angular momentum? The $t_{2g}$ set should be magnetically inactive as well because of being fully filled for Cu(II).


texts: How does lead toxicity from jewelry happen vs. occupational exposure?

texts:
It is known that lead levels in jewelry is a problem, especially for children (https://dtsc.ca.gov/toxics-in-products/lead-in-jewelry/). As a parent with jewelry-loving children I am aware that ingestion or inhalation of dust or any part of the jewelry will be toxic, while simply touching it would not be. However, several sites claim it is dangerous if one touches the jewelry and then touches their eyes, nose, mouth, food, etc and propose hand washing as a solution.
First, I am wondering what form the lead is in when it's found in jewelry metal alloys (not painted) and how exactly it gets to be toxic from there or what happens when you touch it (ions, oxidation?). I can't find any other information online about the form of lead in jewelry. I know it's inorganic lead and was told by friends it's elemental lead*.
Second, I am wondering what is the best way to remove the lead from jewelry exposure from skin? I've read that hand washing with soap and water is insufficient to remove lead from skin according to CDC, NIOSH, and such studies. But these were all focused on PbO from occupational exposure, and not on jewelry exposure (which I presume is not PbO). Is there some difference here that makes regular soap and water effective in this case?
*After reading similar posts on here and here, elemental and metallic lead (what's the difference?) even if ingested does not seem to be as toxic as ionic Pb(II) and covalent compounds of Pb, but there have been and continue to be cases of lead poisonings involving jewelry items, so either it is not elemental lead or elemental lead is more toxic than indicated here.


texts: How does formylation of a nitrogen change the hydrophobicity of a target protein?

texts:
How does formylation, of the sort shown here:

(from this Wikipedia page) affect the hydrophobicity of the target protein?  Can we say anything general about adding a formyl group to a nitrogen?


texts: test tube cracked when added glycerin to potassium permanganate

texts:
I am not expert in chemistry.I learned about combustion in reaction when added glycerine to potassium permagnet.I tried it at home, I took potassium permagnet in test tube and when I added glycerine to it test tube just CRACKED as combustion started.I want to know why, because it lab we some time directly heat test tube, it does not cracked so why this time..

I am not sure I should continue on sulfuric acid and potassium parmagnet test in a TEST TUBE after seeing this affect...

Any Suggestion..


texts: Using the mass of calcium carbonate, what volume of carbon dioxide could theoretically be obtained if the reaction progressed to completion?

texts:
Using the mass of calcium carbonate $m(\ce{CaCO3}) = \pu{0.500 g}$, what volume of carbon dioxide $V(\ce{CO2})$ (in $\pu{mL})$ could theoretically be obtained if the reaction progressed to completion? Assume that the pressure was $\pu{101.3 kPa}$ and the temperature was $\pu{22.5 ^\circ C}$ and that the gas was behaving ideally $(R = \pu{8.314 kPa L mol-1 K-1})$.

I know that I will work with
$$pV = nRT$$
and to bring the $n$ (amount of substance), I have to divide the mass by the molar mass and I assumed that $\ce{CO2}$ mass will be $\pu{0.5 g}$ as well because $\ce{CaCO3}$ will give $\ce{CaO + CO_2}$ so the ratio is $1:1$ so $\ce{CO2}$ mass is $\pu{0.5 g}$, but my problem is that when I bring the amount of substance it should be for $\ce{CO_2}$ or $\ce{CaCO3}$? Because it will differ, $\frac{0.5}{44.01}$ or $\frac{0.5}{100.09}$, that's what I am stuck on.


texts: Is the reaction thermodynamically favored or not?

texts:
$\ce{CO(g) + 2H2(g) +O2(g) <=> 2CH3OH(g)}$,

$\Delta H=-128\ \mathrm{kJ/mol}$
$\Delta S=-409.2\ \mathrm{J/(mol \cdot K)}$

Determine if the reaction if thermodynamically favored.

I just wanted someone to see if my logic is right. Since there are 4 moles on the reactants side and and 2 on the products side the reaction would not be thermodynamically favored because the reaction decreases the amount of entities, which decreases the entropy.


texts: Can mechanical agitation increase the reaction rate?

texts:
The specific example I saw recently was cleansing of concrete (portland cement) film from brick using a diluted muriatic acid. It appeared that the more scrubbing was used, the quicker the cleaning process would go. That seems to match up with everyday experience.

However what is not clear is how that mechanical agitation was specifically improving the reaction rate.

More generally, are there a 'class' of reactions or reagents where mechanical agitation will alter the reaction rate? And is that affecting the actual reaction or more just the process efficiency?


texts: Heat of combustion per mole and per kilogram

texts:
I need to calculate the heat of combustion per mole and per kilogram of complete combustion of, say, X.

I write reaction : $\ce{X + O2 -> ... + Q}$
Find Q using Hess law

Now, what do I do after that?


texts: Distinguish between glucose and Fructose samples

texts: I am looking for a simple way to distinguish between glucose and fructose samples. Currently, I am doing that by melting temperature method. Can anybody suggest me some easy way to do that?


texts:
I have some problems with these properties.
1) Lowering vapor pressure and boiling point.
It happens because the solute molecules take space in the surface of the liquid so a lower number of the liquid molecules change to the gas form. Also the vapor pressure increases when you increase the temperature of the liquid because more molecules get to escape into a form of gas.

So the real question here, What makes boiling point related to vapor pressure?
I have read a lot of articles about that.. The definition of boiling point is the temperature at which the vapor pressure of a liquid is equal to the pressure of the atmosphere on the liquid. Which will rapidly increase the rate of forming gas but why does that happen? It says because of the vapor pressure balanced the atmospheric pressure which makes bubbles form. How does it exactly balance out? Isnt pressure in all directions? How can you be sure that it balances out? Also, Bubbles are created at the bottom of the liquid, How does atmospheric pressure affect it?

2) Same applies to Freezing points.

I need a microscopic explanation. Also without some advanced chemistry complexity.


texts: Best way to clean a gold-plated yoyo bearing?

texts:
I have a gold-plated yoyo bearing which needs cleaning. Most people clean regular non-gold-plated bearings with mineral spirits (naphtha), lighter fluid (hexane/heptane), and acetone, but these gold bearings are somewhat new and we don't have a consensus on a cleaning method. There's debate as to whether the gold plating influences spin time or if it's the precision manufacturing, but they do spin forever and are quite silent. Anyway, these bearings are $22, so constant replacement is an enormous barrier to using these outside of competitions.

I've researched gold cleaning techniques, and all the results say to rinse with water. That's not a very good option since all yoyo bearings have tight spaces where dust gets trapped. To understand this particular bearing's sensitivity: I did try rinsing with tap water last night, and now it barely spins. It seems even the contaminants in the tap water were enough to block up this bearing. Also, while most bearings can be used with a very thin lubricant to prolong life and decrease noise, this one cannot. I could try distilled water, but we really need a precision solution.


texts: What is the effect of adding HCl on a certain solution at equilibrium?

texts:
If we have
  $$\ce{CH3COOH + H2O <=> CH3COO- + H+}$$
   what is the effect on acetate ions when adding each HCl and NaOH to the solution?  (State why according to Le Chatelier's principle)

Le Chatelier's principle states that if any of conditions of a chemical reaction at equilibrium changes, the reaction will shift to a direction to oppose that change and restore the equilibrium.

I guess adding $\ce{HCl}$ will increase hydronium ion concentration so the reaction will be shifted to the left side, accordingly acetate ions concentration will decrease. If we add $\ce{NaOH}$, this will increase water concentration so the reaction will be shifred to the right side accordingly increasing the concentration of acetate ions.


texts:
Following this plan, I am wondering what the byproducts of this method are? At the site with the q-tip, the solution turned a bright yellow, with the q-tip turning a dark yellow, almost red. Holding the q-tip in place for about 10 seconds results in a small amount of smoke, and bubbles around the contact point. What are these colors, smoke, and bubbles? I don't know if the kettle is steel or aluminum, it's an old Budweiser keg, if that helps.

In case the link above dies, the method is etching metal using a vinegar and salt solution, combined with a 9 volt battery. Connecting the negative lead to a piece of metal, and using the positive lead with the solution results in a type of reverse electroplating, thus removing metal ions and etching the metal.

Not sure on the tags for this question, so feel free to adjust them, and the description of the etching method.


texts: Solvation rates of crystalline and noncrystalline materials

texts:
Assuming equal surface area (and other variables), would a highly ordered crystal of some substance dissolve more slowly or quickly than (or at the same rate as) a disordered sample of the same substance?

I immediately thought it would be slower for a crystal to dissolve before thinking about why. Thermodynamically speaking, it should be entropically more favorable to break up the ordered crystal structure, but that doesn't determine kinetics. Kinetically, I think the energy required to break the intermolecular bonds in a crystal would cause the dissolution to be slower.


texts: When using Gaussian to calculate NMR, what's the default solvent and frequency?

texts: If I choose GIAO HF/STO-3G, is the default solvent $\ce{CD3Cl}$? Is the default frequency for $\ce{^1H-NMR}$ 500 MHz? What about the frequency for $\ce{^13C-NMR}$?


texts: Why are H2O asymmetric while CO2 is not?

texts:
What is the reason for water molecules $\ce{H_2O}$ being asymmetric while other molecules like $\ce{CO_2}$ being completely symmetric? See the pictures below:

In both case there is an electronegative difference between the atoms in the molecule. I have read that the angle in the water molecule is always a specific value. Is this a special thing for water or is there a common mechanism I should know?


texts: Direct reaction of fluorine with benzene will give what product?

texts: My book says fluorine will react with benzene vigorously and involve C–C bond breakage. What does that mean and what product will be formed? It also said that the reaction is of no preparative use.


texts: Ideal gasses reaction under const temp and pressure

texts:
Conceptual problem:

Let $A + 2B \rightarrow C + 2D$ be a reaction under constant pressure ($P$) and temperature ($T$), that goes all the way towards the products. $\ce{A,B,C,D}$ are ideal gases. Let $\Delta H$ be the molar enthalpy change in the reaction.
What is the change in the internal energy?

The total amount of moles in the reaction is constant throughout it, can we say that $\Delta U=\alpha nR\Delta T$ is the term for the internal energy? (if so that will be 0).
Another idea is that $PV=nRT \rightarrow V=\textrm{const}$, and then the internal energy equals the sun of chemical work and heat which we know.
All help appreciated.


texts:
This is quite an interesting situation I had thought of. Consider two beakers, each containing $\pu{180 g}$ of water. Also, suppose one of the two has $\pu{1.8 g}$ of glucose dissolved in it. Let's call the one without glucose as A, and the one with glucose as B. I keep a small bell-jar that is large enough to just cover both of the two vessels. Now I will try to measure the vapor pressure inside the jar. Here's a little diagram to show what I mean:

I do not have access to bell-jars or manometers so I'll try to use Raoult's law to find the vapor pressure inside the vessel. The law in a simplified way would be:

$$P_{\text{solution}}=P_{\text{solvent}}x_{\text{solvent}}$$

Where $x$ denotes mole fraction, and solute is considered non-volatile. Keeping vessel A in mind, I get the vapor pressure as 23.8 mmHg, while applying Raoult's law for vessel B, I get the vapor pressure as:

$$P=23.8\left(\frac{10}{10.01}\right)=23.7 \text{mmHg}$$

Now, both of the values can't be true at the same time, and that's what I believe is the paradox.

How can this paradox be resolved?

My thoughts are that perhaps water from vessel A condenses back onto B, thus slowly increasing water content in B, increasing the vapor pressure. However, since theres solute already in B, the vapor pressure can never reach the value provided by the pure water.

What are your thoughts? Does the paradox ever resolve or does it remain in an unbalanced situation?


texts: Why is nitration of veratrole specific in these positions?

texts:
Why do we not need $\ce{H2SO4}$ as an acid catalyst for the di-nitration of veratrole?

Why does the 2nd nitro group go to positions 4 or 5, following the directing effects of the methoxy-group? Doesn't the first nitro group, that has been substituted onto the compound, have any effect on its position?


texts:
for example, if we consider benzene ring ;

all the pi bonds will show resonance and therefore a partial pi bond character will be observed over all the bonds in the ring

my question is

is the c1-c2 bond length equal to c2-c3 bond length???
according to me since they all have equal pi bond character , the bond lengths should be equal
am I right?????


texts: I'm having trouble understanding how to "estimate" the value of the BDE for the compound shown below (I believe it is a secondary benzylic C-Br value) shown below (the 58 kcal/mol). We are supposed to be able to estimate the value from the table values shown below. My teacher said to use the C-H values and C-Br values from the table below to estimate it, but I don't understand how they are able to indicate the value. Any helpful drawings would be nice since I'm new to organic chemistry and have trouble just understanding the names! Thank you.


texts: How does the pH of solutions of salts in which the cation is acidic and anion basic, depend only on the relation of their constants?

texts:
My book is not very explanative about it, I'm trying to get the equation:
$$[\ce{H^+}]=\sqrt{K_\mathrm{w}\times\frac{K_\mathrm{a}}{K_\mathrm{b}}}$$
but I didn't succeed, can someone explain the theory behind and how to get the formula comparing the two ionization constants?
Translation of the actual page of the textbook (Cacace Fondamenti di stechiometria (in Italian)):

Salts which cation has acid features and anions has basic features. A salt like ammonium acetate, $\ce{NH4Ac}$, release after the following (complete) dissociation:
$$\ce{NH4Ac -> NH4+ +Ac-}$$
A cation will behave as an acid and an anion will behave as a base.
In cases like this one, acid-base equilibrium in solution depends only by the strength of the cation compared to the anion. It can be proved

(but it does not, that's why I'm here)

that in first approximation , the concentration of $\ce{H+}$ in those solution is indipendent from the concentration of the salt and it depends only from the comparison between ionization constants of the weak acid and the weak base from which the salt has been formed:
$$[\ce{H^+}] = \sqrt{K_\mathrm{w}\times\frac{K_\mathrm{a}}{K_\mathrm{b}}}$$
From which:
$$\mathrm{pH} = \frac{1}{2}(14 + \mathrm{p}K_\mathrm{a} - \mathrm{p}K_\mathrm{b})$$

It seems to be unclear. I would like to understand the mathematics of the equation that brings the comparison of the two constant became like the one I already wrote. Why is independent from the salt concentration?


texts: I've seen multiple prefixes for naming thiols: mercapto-, sulfanyl-, and -thio. Is there a rule for when specific ones are used? And are they used for IUPAC and/or common naming?


texts: Why do frying pans stick less with heat?

texts:
I know this is simple, compared to most questions asked here, but I notice this several times a week and I'm curious.

I notice if I break an egg and drop it into the frying pan, and the pan is still warming up, the egg sticks to the pan.  But if I wait until the pan is quite hot, and I break an egg and drop it in, the egg barely sticks to the surface at all.

How does the heat make a non-stick surface work better then when it is merely warm or is still warming up?


texts:
It is said that acids react with metal carbonate to form salt carbon dioxide and water.

Sodium carbonate reacts with hydrochloric acid to form sodium chloride , carbon dioxide and water
But if we ionise them then sodium carbonate dissociates to form  two sodium ions and carbonate ion and hydrochloric acid disassociates to form two hydrogen ion and two chlorine Ion so the sodium Ion will combine with the chloride Ion to form NaCl and the hydrogen ions will combine with carbonate ion and form carbonic acid but this doesn't happen and they form carbon dioxide and water.
WHY?


texts: What chemical measurements are related to the degree of flavor extracted by alcohol?

texts:
A recent project of mine includes making infusions of various ingredients to make liqueurs and bitters. Infusions, I've learned, vary widely in the amount of flavor extracted from an ingredient. Citrus zest, for example, can overbear most other ingredients in ways it wouldn't in similar amounts in other recipes.

To better understand the infusing process, I taste a series of infusions every few days, rating the perceived strength of their aroma and flavor. This is clearly subjective, and I'd like an objective, empirical means to check the amount of flavor compounds extracted from an ingredient over time.

The interest isn't in comparing different infusions, but in comparing a single infusion's strength at different times, and against human ratings. Here are a few questions I'd like to be able to answer:

Is this infusion done? Has it extracted as much as we can expect it to?
Has this really changed since yesterday?
Given this measurement, how strongly would my tasters rate this?

Here are some things I've considered:

A refractometer. (Presumably the flavor extracted is the form of dissolved solids, no?)
A proof hydrometer, though I'm unsure if we can reasonably expect proof to change much over the process.
Arduino biometric sensors for things like e.g. pH, though I'm again unsure of the expected relationship.

Are these, or any others, reasonable measures of an infusion's progress?


texts: A dehydrating agent acting as an hydrating agent?

texts:
We know that $\ce{P4O10}$ is a dehydrating reagent and I might list on 100's of reaction of it's dehydrating nature, mainly orgainc elimination reaction and few inorganic oxoacid dehydrations, but it is acting like a hydrating agent, cf. these:
$$\ce{PCl5 +P4O10->POCl3}$$

  "Phosphorus pentachloride also forms $\ce{POCl3}$ by reaction with water, but this reaction is less easily controlled..."


texts: What is the molecular structure of polymetatelluric acid?

texts:
Telluric Acid, $\ce{Te(OH)6}$, dehydrates to form polymetatelluric acid: $\ce{(H2TeO4)10}$. However, I have been unable to locate the exact structure of polymetatelluric acid, and it does not seem entirely obvious.

Are the tellurium centers connected directly to each other or are they separated by oxygen? Are these polymeric bonds single bonds or double bonds or some mixture of the two? My best guess is that the $\ce{Te}$ centers are separated by oxygens with three other oxygens surreounding each $\ce{Te}$ center, two of which are $\ce{-OH}$ groups and the third being a $\ce{=O}$ group: this would make the oxygens between the $\ce{Te}$ centers alternating single and then double bonds — possibly conjugated on some level. Is there any chance polymetatelluic acid has direct $\ce{Te-Te}$ bonds?


texts: Why do alkenes react with oxidising agents?

texts:
My book says :

  The high electron density associated with the double bond means that
  alkenes are attacked by oxidising agents.

And I dont understand how the high electron density in the double bond causes that.


texts: Why must the forward reaction and the backward reaction follow the same pathway?

texts:
It is often claimed that a (normal) catalyst catalyzes the forward and the backward reaction to the same extent, so the equilibrium position is not shifted.

I would like to ask why must the forward reaction and the backward reaction follow the same pathway?

I could imagine a mechanism for this reversible reaction from $A$ to $D$:

$$\ce{A <=> D}$$
$$\ce{A -> B<=> D}$$
$$\ce{A <=> C <- D}$$

So that the forward reaction and the backward reaction must follow different pathways, as one step of both pathways are irreversible.

Is this scenario impossible in reality? If so, why? If not, is there any example in real life?


texts: Does Dean Kamen's Slingshot really filter virtually everything?

texts:
According to Dean Kamen (in the movie http://www.imdb.com/title/tt3242934/) and on the Net (http://www.popsci.com/article/science/pure-genius-how-dean-kamens-invention-could-bring-clean-water-millions) his device that uses pressure-Distillation to purify water, it would work with virtually any water and render medical-grade pure water.

I have a hard time to believe this as:
-chemicals could evaporate before water and so get into the distilled water
-I have no idea how he keeps the distillation chamber clean (prefiltering?) so it does not clog.

So I would like to know what are the limitations of distilling water to purify it?

I know that distilled water cant be drunk as it is without adding salts. I like the project of Mr. Kamen very much, I just want to know the boundaries, as the promises ("Fill in anything that is wet") seem way to optimistic.
Thx


texts: Why is silver chloride less soluble than silver nitrate?

texts:
Related: Reaction between silver nitrate and aluminum chloride

Experimentally, $\ce{AgCl}$ is insoluble in water, but $\ce{AgNO3}$ is soluble. They're pretty common in a lab (well, $\ce{AgCl}$ is a common precipitate)--so I think most of us know this.

By Fajan's rules, on the other hand, larger anion $\implies$ more polarization/covalent character $\implies$ less solubility. But, $\ce{NO3-}$ is the larger anion, yet $\ce{AgNO3}$ is more soluble.

Is there any theoretical reason for this?


texts: Reaction of cinnamic acid with Br2/Na2CO3

texts:
The first reaction produces benzaldehyde, and the next one (perkin's condensation)produces Cinnamic acid.(X)
Now the treatment of X with $\ce{Br2/Na2CO3}$ is whats troubling me.  $\ce{Na2CO3}$ being a base, abstracts the hydrogen from the  $\ce{COOH}$ group.  $\ce{Br2}$ reacts with the alkene portion to yield a cyclic intermediate. What next?
The solution claims that somehow The  $\ce{CO2-}$ group leaves and a bromoalkene forms. The addition Of moist KOH in the next step results in  $\ce{E2}$ elimination to yield option (c).
I cant quite digest the $\ce{CO2-}$ group leaving. I thought of a mechanism, which is similar to the syn-elimination in esters: but that doesnt work out well..
Any hints/ insights will be appreciated. The correct answer is (c).


texts: Why does hydrogenation of this compound not result in a diastereomeric mixture?

texts:
In a question, this compound was given and it was asked:
"Hydrogenation of the above compound in the presence of poisoned Palladium catalyst gives?"

When I was answering it, I thought that the Lindlar catalyst would partially reduce the alkyne to give a cis alkene which would create two compounds that look like this:

Clearly, compound I is optically inactive due to the presence of plane of symmetry but compound II does not have any such plane of symmetry so it must be optically active. Hence, I answered that the resulting product would be a diastereomeric mixture since I and II are diastereomers wrt each other.
But, the solution to the question suggests that only compound I forms, with no explanation given for why compound II does not form. Searching on the net was also of no help. Could someone provide an explanation?
Thanks for your time and apologies for the sloppy drawings.


texts: Best place to take off vacuum for distillation

texts:
I have seen vacuum take-off adapters that are essentially plugs, which could be placed at the top of a three-way above the fractionating column, and also straight and bent vacuum take-offs with an inner stem that seem meant to be placed right before the collection vessel.

Would there be any difference in which place is better to vacuum from? Would it be best to maybe use a T-connector on the vacuum line and vacuum the top of the fractionating column as well as the collecting flask?


texts: Why does moist air have lesser density than dry air? When the amount of vapor inside increases, the mass increases and hence won't the density as well increase?


texts: When do one have to actually calculate the net charge of an amino acid?

texts:
When the pH and the pKa levels differ by 2 or more you don't need to calculate the net charge. What you do then is to just count the negative and positive charge and add them up.
When pH=pKa you also don't need to calculate, because you get half of the different types.

BUT what about if we want to know the net charge for an amino acid where one of the groups have an pKa value of 4,25 , when the pH is
a) 4,0  , b)5 , c) 5,5 and d)6
Do you have to calculate it for all of these? Can you say that since a) is pretty close to the pKa we consider them the same, or that since d) is pretty close to being 2 units more, we can just say that and make it easier? And is there even really a point in calculating for c) when it's more than 1 pH unit over?

My question is basically: where do I draw the line?


texts: How to construct spin free coefficient of 2-hole 1-particle configuration?

texts:
It is clear that we can expand a cationic state of a molecule in terms of configuration interaction (up to double excitation). It means:
$$|I \rangle = \sum_j c^{(I)}_j a_j|\phi_0 \rangle \ + \ \sum_{r,k<l} c^{(I)}_{rkl} a_r{\dagger} \ a_k \ a_l|\phi_0 \rangle \ + \ ...   $$
where C are coefficients, $a_i(a^{\dagger})$ is annihilation (creation) operator, and $|\phi_0 \rangle$ is HF Ground state of nuetral molecule.
I would like to know how can I construct spin-free $c^{(I)}_{rkl}$, which is the coefficient of 2h1p configuration? Particularly, I interested in this procedure when cationic state and accordingly 2h1p configuration is doublet.


texts: Am I Using the Correct Number of Significant Figures (Heat Problem)?

texts:
The question is:

  A patient arrives in the emergency room with a burn caused by steam. Calculate the heat, in kilocalories, that is released when $\pu{18.0 g}$ of steam at $\pu{100 °C}$ hits the skin, condenses, and cools to body temperature of $\pu{37.0 °C}$.

1) I solve for the steam as it condenses:

Heat of vaporization: $$\Delta H_\text{vap}(\ce{H2O}) = \pu{2260 J/g}$$

Heat: $$\begin{align}Q_1 &= \pu{18.0 g} \times (\pu{2260 J/g}) \times (\pu{1 cal/4.184 J}) \times (\pu{1 kcal/ 10^3 cal})\\ &= \pu{9.722753346 kcal} \to \text{rounded to 3 SF} = \pu{9.72 kcal}\end{align}$$

2) I solve for the cooling of the $\ce{H2O}$:

Specific heat capacity: $$c(\ce{H2O}) = 4.184\ \mathrm{J/(g\ ^\circ C)}$$

Temperature change: $$\Delta T = \pu{100 °C} - \pu{37.0 °C} = \pu{63 °C}$$ (2 SF)

Heat: $$\begin{align}Q_2&=\pu{18.0 g} \times \pu{63 °C} \times 4.184\ \mathrm{J/(g\ ^\circ C)} \times (\pu{1 cal/4.184 J}) \times (\pu{1 kcal/10^3 cal})\\&= \pu{1.134 kcal} \to \text{rounded to 2 SF} = \pu{1.1 kcal}\end{align}$$

I then add the two results together and get:

$$\begin{align}Q&=Q_1+Q_2\\&=\pu{9.72 kcal} + \pu{1.1  kcal} = \pu{10.82 kcal}\end{align}$$

$\to \text{rounded to 3 SF} = \pu{10.8 kcal}$ (using the addition/subtraction rule for SFs)

The textbook's answer is $\pu{11 kcal}$.

Is my answer right, according to significant figure rules, or is the textbook's provided answer correct?


texts: What studies show that d orbitals don't play an important role in covalent bonding? (> period 2 elements)

texts:
Take a look at all the following molecules: $\ce{SO3^{2-}}$, $\ce{SO2}$, $\ce{SO4^2-}$, $\ce{PF5}$ and many more you can add. In all these there is a controversy of one of these two types:

Is formal charge more important than octet rule - as to justify hypervalency- on determining Lewis structure? As a rule I'd say the answer is no. For example in $\ce{SO2}$,$\ce{SO3}$, $\ce{SO4^2-}$, Do calculations show it?
What is the central atom hybridization? For example, in $\ce{PF5}$ (see here). Does it involve d-orbitals?

In any case, both previous statements are related to the d-orbitals energy.

There is -at least- one straightforward way to answer the question:

Calculate* the Molecular Orbitals and see which of previous options fit better (the use of d-orbitals or the non use of them).
*sure some can be found in some papers.

So the question is:

Are there theoretical studies of many concrete examples as to remark that d orbitals don't play any relevant role in covalent bonding?


texts: Determining Kohn-Sham and Hartree Fock virtual orbitals: The underlying field

texts:
In Frank Jensen Introduction to Computational Chemistry from 2007, I stumbled upon this paragraph about whether to assign meaning to the KS orbitals or not

  Another difference is that the unoccupied orbital energies in Hartree–Fock theory are determined in the field of N electrons and therefore correspond to adding an electron, i.e. the electron affinity. The virtual orbitals in density functional theory, on the other hand, are determined in the field of N − 1 electrons and therefore correspond to exciting an electron, i.e. unoccupied orbitals in DFT tend to be significantly lower in energy than the corresponding HF ones, and the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) gaps are therefore much smaller with DFT methods than for HF. This also means that orbital energy differences in DFT are reasonable estimates of excitation energies, in contrast to HF methods where excitation energies involve additional Coulomb and exchange integrals.

I can't seem to understand why the Kohn-Sham equations are solved in the presence of N-1 electrons and not N. From my understanding the Kohn Sham and the Hartree Fock equations are almost identical. Where does this difference come from?


texts: How fast will hydrazine boil out of a tube into a vacuum?

texts:
For context I'm talking about ISEE-3 and how long it would take to dump the now useless and hazardous fuel it still carries.

Given a heated tank of hydrazine (somewhere near $0~^\circ\mathrm{C}$) connected by way of a long slender unheated tube to a infinite high vacuum, how fast will the tank vent to ~zero pressure?

My guess is that rather quickly, the boiling action will produce a plug of frozen hydrazine in the tube. Once that happens, the sublimation on the outer face will cause condensation and/or solidification on the other face and the plug will walk back towards the tank until it either reaches it or the solid portion of the plug get to thin in which case it will burst and vent like in the beginning and start over.

The question is, how fast will this happen?

Edit: on further inspection, it looks like the "tube" may be heated after all.


texts: I'm looking into plastics and how they break down. I have learned 3 ways oxo-biodegradation, photodegradation and thermaldegradation. Does anyone know how PET (polyethylene terephtalate) degrades?


texts: Hydrophobic interactions and Gibbs Free Energy

texts:
I want to understand the basis of the hydrophobic effect.
In biochemistry, protein structures are often explained in terms of hydrophilic and hydrophobic effects.  The hydrophilic interaction is understandable in terms of electrostatic interactions but I don't understand the nature of the hydrophobic effect.
I have seen explanations in terms of the Gibbs free energy of a system. For example, if I take an oil and water mixture we know the mixture spontaneously separates, but what are the forces involved?
I get it in terms of Gibbs Free Energy:
$\Delta G = \Delta H -T \Delta S$
If the oil and water mixture is shaken so that there is an emulsion and then it's left to settle, hydrogen bonds are broken and form to the value of $\Delta H$.  I assume that more hydrogen bonds are formed as water and oil separate but I believe that the main driver is entropy.  Overall the entropy change is positive because the ordered structure of water bonds around each individual fat droplet are broken down and entropy increases, and hence $\Delta G$ is negative. OK, but to me that does not explain why individual fat particles to move.  If there's a change in inertia, then there's a force?  What is the force?
I can accept this explanation on an energetic level but what forces are acting on the oil droplets to effect this?  I can't see any Coulomb forces here.  Whilst I can accept that energetically it might make sense for oil and water to separate, I feel I need a force to explain why matter moves.  Could someone explain what the nature of the hydrophobic interaction is because I don't understand at present.
Thank you.
My explanation was taken from this link: https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Physical_Properties_of_Matter/Atomic_and_Molecular_Properties/Intermolecular_Forces/Hydrophobic_Interactions#:~:text=Hydrophobic%20interactions%20describe%20the%20relations,example%20of%20this%20particular%20interaction.
Edit:  I note someone asked the exact same question.  I didn't see it before but I don't think it's been answered.
How does the entropic force arise within the hydrophobic effect?


texts: Separation of Noble Metals for scrap recovery

texts:
I am researching scrap metal recovery as a side job and am hitting a wall with the noble metals. Gold, Silver, Platinum, and Palladium seem like they're all fairly easy to recover. I just can't find a process to separate the rest (Re, Ru, Os, Ir, Rh), not even a description of the industrial processes.

I suppose what I'm looking for is a full reactivity series for these metals, and any lead on a separation process.

Eventually I'd like to expand this to all transition metals (Scandium is more valuable than Platinum from what I've read) and the Lanthanides. So any info down that rabbit hole would be appreciated too.

I appreciate the time of whoever answers here. I can get my business off the ground with the knowledge I already have, but adding that extra recovery of trace noble metals would add an element (pun intended) of fun as well. I'd hate to see all that dust go to waste.


texts: Nanoparticle Alloys (Gold-Silver) not forming

texts:
I have synthesised what I thought were gold-silver alloys at various different compositions.
The UV/vis data showed that nanoparticles alloys with a majority of the composition made from gold had one plasmon band, indicating they were alloys.
However with nanoparticle alloys where the composition is mainly silver, the UV/vis data shows two plasmon bands, indicating the presence of segregated gold and silver nanoparticles which are not alloyed.

Could anyone explain why this has happened?


texts: Extraction of monosodium glutamate (MSG) from kelp

texts:
What is the extraction process of monosodium glutamate (MSG) from kelp?
How could one do this at home?
Is there a specific kelp species to use?


texts: Why does hydration of ions depend on their charge to area ratio?

texts:
The following is written in my book Concise Inorganic Chemistry by J. D. Lee.

Hydration energy, hydrated radius and hydration number of a particular ion depends upon charge per unit area. Hence their order is the same for the following cations in the given examples:
$\ce{Li+(aq) > Na+(aq) > K+(aq) > Rb+(aq) > Cs+(aq)}$

And other similar examples are also given. My question is, why does charge to surface area ratio matter? The force felt by the water molecules due to any of these cations should be the same due to shell theorem. Also, a cation of bigger size can accommodate more water molecules in its vicinity due to its size. Then still why does an increase in charge to surface area ratio corresponds to an increase in hydration tendency?


texts: Shouldn't cyclopropenyl anion be aromatic as it will keep its lone pair in an unhybridized orbital? My teacher says that the lone pair will be a part of a hybrid orbital and the compound will be anti-aromatic.


texts:
I'm wanting to make  a Pine-Sol scented candle.  However, in candle making you have to add a fragrance oil.  People make them all the time by adding vanilla, etc and canola oil, vegetable oil, etc.  I'm wondering what proportions I need to do this with Pine-Sol since it has chemicals in it??  I'm using the Original Pine-Sol - it contains 8.7% Pine oil in it if that helps.  That's all I got from the label.

Thanks for your help!
Mandy


texts: How can I check the sodium content of food?

texts:
What is an easy (i.e., home project) way to measure sodium in food?

For example, the nutritional label of a tahini brand that I often consume shows very little sodium (around 10mg/100g). I suspect the sodium content is much higher.

What is the chemical way to measure the salt content?


texts: Finding the concentration from a dilution

texts:
This must be a very basic question but I have gotten confused over it.
How would I find the concentration of each component of the reaction for each experiment from this data? I am guessing it can’t be the concentrations given, is that for some stock solution?


texts:
I am having issues understanding the consequence(s) of a decrease in pressure on a chemical reaction.

I have understood that when we increase the pressure, the side having more number of moles wants its moles to go to the other side where it is more empty(this is how I learnt it). But I fail to understand why if we decrease the pressure by increasing volume the side having less moles goes to the side having more moles?

Also in the case of adding inert gases why does the equilibrium shift in the direction in which larger no of moles of gas are formed?


texts: Why does an increase in reduced mass lead to a decrease in frequency?

texts: In terms of IR spectrum, why does an increase in reduced mass lead to a decrease in frequency?


texts: Is it a coincidence that pKw = 14.00 at SATP?

texts:
High school chemistry student here. For our purposes in class for studying acids and bases, we are taught that $\text{p}K_\text{w}=14.00$, which is central for many of our calculations. I assume this is the value for room temperature and standard pressure.

However, it seems awfully suspicious that the negative $\log$ of an equilibrium constant should turn out to be a whole number. Is this just a useful coincidence? Or have scientists pulled some clever tricks, ex. by defining "room temperature" to be the temperature such that $\text{p}K_\text{w}=14.0000...$?


texts: Sample preparation for UV analysis of drug content in capsules/tablets

texts: I want to analyse the drug content of a sample of gelatin capsules filled with active drug (declared dose is known) and excipients such as lactose monohydrate, microcrystalline cellulose etc. with UV spectroscopy. However I have a question about the sample preparation of my capsules. So first what I want to do is dissolve the capsule content in an organic solvent (such as ethanol, chloroform etc.) because the solubility of the drug is bad in water, and then dilute the samples to a concentration which is suitable for UV analysis. The problem is that when I dissolve the content of the capsule, I'll likely get a suspension where the excipients won't dissolve in the organic solvent. This would interfere with my UV analysis. So I was wondering if it would be a good idea to centrifuge the samples, or just wait for it to precipitate on its own? And if centrifuge, would it be better to first centrifuge the stock solution and then dilute or first dilute and then centrifuge the acquired diluted solution? Thanks in advance.


texts: Why can one product in an equilibrium system not be produced without the other?

texts:
I performed an experiment where $\ce{CuSO4 (aq)}$ reacted with $\ce{NH3 (aq)}$ in one test tube, and in the other, $\ce{CuSO4 (aq)}$ reacted with $\ce{NH3 (aq)}$ and $\ce{NaOH (aq)}$. I know two products were formed, one being the complex ion $\ce{[Cu(NH3)4]^{2+}}$.

The goal of the experiment was to see if one of the products could be produced without the other, and I know that is not possible due to the solutions being at equilibrium, but why is this?


texts: Ester as a side product in the synthesis of bromoalkane from alcohol. Is it correct?

texts:
About 5 months ago, I answered a very interesting question albeit a very simple one.

  Why do we need sulfuric acid in creating alkyl bromide and not in creating alkyl iodide from alcohol and hydrogen halide?

The question was why sulfuric acid is used to convert any alcohol to bromoalkane but not iodoalkane. Jan's answer quite pointed out the explanation:

  hydrogen iodide is sufficiently acidic to protonate the corresponding    alcohol and drive the reaction. More acids are not
  needed.
  hydrogen bromide is not acidic enough to drive the reaction. Adding    sulphuric acid protonates the alcohol partially and allows the
  reaction to proceed.
  in the case of weakly soluble alcohols and hydrogen iodide, phosphoric acid may be used instead since it does not oxidize iodide (while sulfuric acid does).

Though I am satisfied with Jan's excellent answer, I further pointed out that sulfuric acid may react with hydrobromic acid to form bromine(aq.) and sulfur dioxide. This bromine may oxidize alcohol to form aldehyde and carboxylic acid and they two will form ester. This was my proposed explanation but I couldn't find any experimental result to back my explanation and heavily relied on theory.

Now recently Nurdrage, a renowned chemist famous for his synthesis of pyrimethamine has uploaded a video on Youtube about the synthesis of bromoethane and bromohexane from ethanol and hexanol using sulfuric acid. He also explained the concern of forming bromine as side product from the reaction of hydrobromic acid and sulfuric acid. He showed a purification technique by adding sodium bicarbonate to react with bromine to form sodium hypobromide.

Now my question is:

Is my explanation of forming ester instead of bromoalkane correct enough? Is there any possibility of forming minute amounts of ester? The reaction may be slow but it can happen before any purification is done (reacting bromine with sodium bicarbonate). If so, what can be done to remove any ester or prevent the reaction of ester formation?

Also related: Why is alcohol boiled with HBr for preparing alkyl bromide?


texts:
What is the physical meaning when we have an empirical formula with fractional subscripts such as $\ce{LiMn_{1-x}Fe_{x}PO4}$ $(0 \le x \le 1)$?

This an example of the paper the notation above is used:

Bai, J.; Hong, J.; Chen, H.; Graetz, J.; Wang, F. J. Phys. Chem. C 2015, 119 (5), 2266–2276. DOI 10.1021/jp508600u.


texts: I work in a manufacturing company specializing in polyethelene foam and I have been struggling to separate butane from air in our warehouse during curing period where all the butane gas used to make our product is just released in the air. I have been thinking of ways how to separate and recycle the butane? Can someone help me?


texts:
I'm interested in the melting point of ocean salt. While sodium chloride has a melting point of 801 °C, ocean salt contains 15 % other ions, mainly sulphate, magnesium, calcium and potassium (the exact composition seems to differ depending on the water source).

Does ocean salt form a eutectic mixture with a lower melting / boiling point? Are there perhaps publications actually testing ocean salt melting points? Thanks!


texts:
What is the $\ce{[HPO4^2-]}$ of a solution labeled "$\pu{0.10 M}$ Phosphoric Acid"? Given the $K_\mathrm{a}$ values of $7.1 \times 10^{-3}$, $6.3 \times 10^{-8}$ and $4.2 \times 10^{-13}$ for the first, second and third ionizations, respectively.

Some sources have shown that the answer is $6.3 \times 10^{-8}$, but following through the long calculation through each ionization to get the equilibrium concentration of $\ce{HPO4^{2-}}$ I get an answer of $3.8 \times 10^{-5}$. Hoping someone can enlighten me on this matter.

Attempt at solving:

So first what I did was to individually find the concentrations using the given $K_\mathrm{a}$ values. Working from the top, I calculated for the concentration of $\ce{H2PO4-}$ from the given concentration of $\ce{H3PO4}$. Had to go quadratic with this one since the first ionization constant is a relatively big number. After getting the concentration of $\ce{H2PO4-}$, went on to get the concentration of $\ce{HPO4^2-}$.

After this one, used the final ionization constant to get the concentration of $\ce{PO4^3-}$ produced, which I found to be so small that the $\ce{HPO4^2-}$ from earlier isn't all that much affected. And after all that I get the answer of $\pu{3.8e-5 M}$ for $\ce{HPO4^2-}$.


texts: pi-type bonding interaction along the bond

texts:
I was given the diagram of $\ce{BF3}$'s LUMO and asked to assess its bonding character as shown below:

Below is the model answer for the annotated version.

I managed to correctly answer the HOMO MO with the same annotations but was confused here slightly.

The LUMO Interaction shows a $\ce{p}$ orbital coming out of the plane, where the B p orbital is out of phase with the $\ce{F3}$ fragmnet orbitals, but the model answer suggests there is a $\ce{\pi}$ type bonding interaction.

This does not make sense to me.
Unless mistaken, I thought the p-orbitals from the B and the F atoms (given they are out of phase) show along the bond $\ce{\pi}$ type antibonding properties, rather than $\ce{\pi}$-type bonding interaction.

Am I correct or not? How is there $\ce{pi}$-type bonding interaction possible along the bond here?


texts: Significant figures in a calculation of atomic mass from isotopic abundance

texts:
I had this question:

Naturally occurring europium consists of two isotopes with a mass of 151 and 153. Europium-151 has an abundance of 48.030 and, and europium-153 has a natural abundance of 51.970. What is the atomic mass of europium? Do not include units. Be sure to round to the correct number of significant figures.

So I do the math for the calculation:
$(151 \times 0.48030)+(153 \times 0.51970) = 152.0394$
I submit 152.0 because, as I understand it, the products of the math in the parentheses should be considered to have 3 sig figs each - ending in the tenths place. So when I add those two sums up, it should end in the tenths place too given addition/subtraction sig figs rules. This is marked as incorrect, and I worry I am misunderstanding something.
I emailed the professor, and he said it was a word question and I needed only to select the fewest sig figs of the ones provided (151 and 153 have 3), so my answer should have been 152 without the 0 in the tenths place. Is this usually the case? What confuses me is I don't think I was allowed to do this for other word problems, but I could be wrong. Is there a difference between word problems and other problems, and is 3 really the amount of sig figs I should have had?


texts: Why does the reference electrode in potentiometry have a diaphragm?

texts: I am studying about potentiometry and pH-measurement with a glass electrode. I don't understand why the reference electrode has a diaphragm and is immersed in the measured solution. If I got it right, there is no current flowing and the composition of the buffer inside the reference electrode is constant. Why should it then be connected with the solution? Can someone clarify?


texts:
I have been asked to determine the major product for the reaction:

From the reagent given, one can tell that this is an epoxidation reaction. But, as only one mole of the peroxyacid is given, epoxidation can only take place in one of the two bonds.
How do you determine on which double bond the epoxidation will take place?


texts: Will heating alumina (Al2O3) to its melting point yield pure Al?

texts:
My inorganic chemistry is at a basic level, so my question is, if I heat alumina ($\ce{Al2O3}$), to its melting point around 2000 C, will I wind up with pure Al?  I think the oxygen will release from the $\ce{Al2O3}$ when the temperature approaches 2000 C.

I bought 5 kilograms from a friend who works at a refinery near my town (he works in logistics and does not have a chemical background) with 1.75$ of almost pure alumina ~99.95%, and I want to know if I melt that white powder will I obtain 2.5kg of 99.95% aluminium?


texts:
I was reading Jan's answer to the following question-:
Why can NCl3 be hydrolyzed but CCl4 cannot?.
Since nitrogen is less electronegative than fluorine in $\ce{NF3}$, the electrophilic site is the Nitrogen atom. That means the water molecule should attack nitrogen atom in an $\mathrm{S_N2}$ manner. The stearic crowding around the atom is also less. Then why is the reaction not taking place? Is it only because fluoride ion is a poor leaving group due to its high basic strength?


texts: Why are ionic reactions very fast in aqueous medium?

texts:
(No, I am not talking about why Ionic Reactions are faster than Covalent reaction.)

This question has me stumped. I mean, at first it looks obvious; water is polar in nature, but what exactly does that help with?  Also, can ionic reactions even happen in non-aqueous mediums?


texts: What is actually meant by that concentration of reactants and products remain constant in equilibrium?


texts:
A half-reaction on one of the electrodes in a battery produces free electrons (for example) and consumes anions (or produces cations). I understand why, if there's an external wire for electrons to travel on, there needs also to be a salt bridge for ions to travel on inside the battery, and if there isn't, the electrons will soon stop flowing due to separation of charge building up.

However, since each half-reaction on its own is charge-balanced, what stops the half-reaction from just continuing to happen even when the circuit is open? Why for example in an alkaline battery Zn won't continue to react with OH- abundantly coming from the electrolyte?


texts:
What is the chemical explanation for pennies in vinegar turning green? What is the explanation at a macroscopic and atom-molecular level?

The procedure is:

Fold a paper towel so that it fits inside a dish.
Place a penny on the paper towel.
Pour vinegar over it so that the paper towel is fully saturated.

Experiment


texts: Why does iodine solution turn transparent on adding base?

texts: Yesterday in biochemistry lab when I added sodium hydroxide to iodine solution. The iodine turned transparent. Can someone please explain why is this happening?


texts: How does association within vapor or dissociation within liquid affect the ideal nature of a binary solution?

texts: As I understand, when there is positive deviation of a binary solution from Raoult's Law, the equilibrium partial pressure curve approach ideality (i.e a straight line dependence of equilibrium partial pressure and pure component vapor pressure) when the mole fraction approaches unity for any one the components. This is true except when there is association within vapor or dissociation within liquid. What is this association and dissociation and how does this affect the ideal nature?


texts: Determination of structure by 13C and 1H NMR spectroscopy

texts:
I'm trying to interpret a $\ce{^{13}C}$-NMR and $\ce{^1H}$-NMR spectrum. So far, I've decided that $\ce{CH3-C}$, $\ce{CH2-CH3}$ and $\ce{CH-CH}$ exist in the structure. I'm not sure but I guess there should be different seven carbons too.

I've come up with the structure below but I feel like there is not enough information to be sure. What should I need to consider to go further at this point?


texts: Difference between Force Field and topology, and other related questions

texts:
I am performing some Molecular Dynamics computer simulations and I am learning about the various Force Fields (FF) such as OPLS-AA, OPLS-UA, AMBER, etc.
Many things are still unclear to me. I put these questions together because I think they are strictly related.

1) What is exactly the difference between "Force Field" and "topology", since they define similar parameters?

2) Which parameters can be defined as "belonging" to the FF, and which not?  It seems to me that sometimes topology files recall atoms from the force field and edit some parameters such as charge, mass, bond lengths, elastic constants.

3) Why is water model usually considered separately from the FF, and why is it not included in it?

4) When a molecule does not belong to a known topology and we have to model it, how do we establish the compatibility between our model and the FF used for the other molecules in the same simulation?

Thank you.


texts: Why does diamond conduct heat better than graphite?

texts: Our teachers made us accept (without any explanation) that diamond conducts heat better than graphite. What is the reason behind this (alleged) fact?


texts: Difference between Resonance Effect and Mesomeric Effect

texts:
While studying electron displacement effects in organic chemistry, I read that the Resonance Effect and Mesomeric Effect are the same. Every source I checked used the heading or opening "The Resonance (or Mesomeric) Effect is..."

However, I was able to find the difference between Resonance Structures and Mesomeric Structures is and found out that the two differ in how they depict conjugated pi bonding. The Mesomeric Structures are all the compounds with all possible arrangements or the pi bonds drawn separately. The Resonance Structure is one diagram that uses dashes and lines to denote the partial double bond characters in the compound.

So my understanding from this difference between the structures is that the effects must only differ in how they are depicted. But I was unable to find a source that could help confirm this. Can someone please confirm or explain it for me?


texts: Isn't the change in entropy zero for a reversible process?

texts:
I'm calculating $\Delta G$, $\Delta H$ and $\Delta S$ when an ideal gas expands isothermally and reversible at $20$°C from  $5$ MPa to $1$ MPa. I used the relation that:
$$\left(\frac{\partial G}{\partial P}\right)_T=V$$
This relation can be shown from the defintion $G=H-TS$. Then I integrated G so that:
$$\Delta G=\int_{P_1}^{P_2}VdP$$
We have an ideal gas $=>V=\frac{RT}{P}$. Which gives us that:
$$\Delta G=\int_{P_1}^{P_2}\frac{RT}{P}dP=RT\ln\frac{P_2}{P_1}$$
If you calculate this you'll get that $\Delta G\approx3.9$ kJ/mol. This was correct.
However I then tried to calculate $\Delta H$. Since $dH=dQ+VdP$ and $dQ=TdS$:
$$dH=TdS+VdP$$
After this we know that we have a reversible process which according to me means that $dS=0$. Which means that $dH=VdP=dG=>\Delta H=\Delta G$. However the answer was that $\Delta S= 13.38$ J/(Kmol) and $\Delta H=0$. How is this possible? Isn't $dS=0$ for a reversible process?


texts: How to derive the compressibility factor for a van der Waals gas?

texts:
So as far as I know,
$$Z=\frac{p_\mathrm{r}V_\mathrm{r}}{nRT},$$
where $\mathrm{r}$ denotes the subscript for real.

Solving it for a van der Waals gas gave me the following result,
$$Z=1+\frac{p_\mathrm{r} b}{RT}-\frac{an}{VRT}+\frac{an^2b}{V^2RT},$$
where $V$ is the volume of the container.

This doesn't quite tally with the form I see in the textbooks.
Where am I going wrong?


texts: How to calculate core electron SCF Fock Matrix Elements?

texts:
I have searched everywhere but there are no worked examples of how to calculate the $\langle\chi_i |\hat{h}| \chi_j \rangle $ values for the Fock Operator using the SCF HF Roothaan method. I am given a wavefunction that is expanded as a set of basis functions, but I don't know how to apply the second derivative to something like
$$
\phi_0(x) = \sum_{\nu=1}^{4} c_{\nu}e^{-kx^2}
$$
Where we assume this is a system with two (spin-1/2, anti-aligned) particles under a harmonic oscillator potential, giving us a total Hamiltonian
$$
\hat{H} = -\frac{1}{2} \frac{\partial{}}{\partial{x_1^2}} + \frac{1}{2}kx_1^2 -\frac{1}{2} \frac{\partial{}}{\partial{x_2^2}} + \frac{1}{2}kx_2^2
$$
I am capable of calculating the overlap matrix elements for something like this, where I would get a matrix
$$
S =
\begin{bmatrix}
S_{11} & S_{12} & S_{13} & S_{14}\\
S_{21} & S_{22} & S_{23} & S_{24} \\
S_{31} & S_{32} & S_{33} & S_{34} \\
S_{41} & S_{42} & S_{43} & S_{44}
\end{bmatrix}
$$
Where each matrix element is
$$
\langle\chi_i|\chi_j\rangle
$$
Unfortunately, I am stuck when it comes to $\hat{H}|\phi_0\rangle$. I am not sure where the $x_1$ and $x_2$ terms come from in the Hamiltonian. I understand that $\phi_0$ represents the orbital that the electrons occupy, but when expanding the wavefunction into the basis set, how do we get the different $x$ terms?
Sorry if none of this makes sense, this is the product of many online learning deficiencies.


texts: Is there an easy explanation of MP2 calculation

texts:
for my master thesis I calculated some ring strains with MP2 calculation. It was not hard to calculate these things but I'm struggling to understand what the theory is about. Now I'm defending my work and I'm affraid that my professor asks questions about it.

So is there an "easy" way (not really easy but maybe without some hardcore quantum mechanics) to expain the MP2 calculation so an organic chemist can understand it?

Are there any good reasons to use MP2 instead of B3LYP or other DFT calculations?
A friend in theoretical chemistry suggested MP2 but we never talked about why.

Thank you for your answers.


texts: Measuring the % of pectin in a fibre after enzymatic treatment with pectinase

texts: I will remove the pectin from hemp fibres with Bioprep 3000L pectinase. How can I measure the % of pectin before and after for loose fibres? I only found a way to measure it for fabric, but I will perform this test on just loose hemp fibres.


texts: What is Drago's rule? Does it really exist?

texts:
My textbooks states the Drago's rule in inorganic chemistry as follows:

  The more electronegative atom prefers the orbital having more p
  character, and lone-pairs or less electronegative elements prefer such
  orbitals, as have more s character.

  Now, according to hybridization, $\mathrm{sp^3d = sp^2 + pd}$,
  $\mathrm{sp^3d^2 = sp + p^2d^2}$, $\mathrm{sp^3d^3 = sp + p^2d^3}$

  So, in $\mathrm{sp^3d}$ more electronegative elements like Fluorine go
  to axial position, but such elements go to equatorial position in
  $\mathrm{sp^3d^2}$ or $\mathrm{sp^3d^3}$.

  Also, as a result of Drago's effect when atoms of group $14, 15$ and
  $16$ (belonging to third period and above) are attached to atoms having Electronegativity less than
  $2.5$ then it has valence electrons in pure s-orbitals. And apparently
  no hybridization effect is observed in such cases. That is why in
  $\ce{NH3}$ the bond angles are $107.8^\circ$ but for
  $\ce{PH3},\ce{AsH3},\ce{SbH3},\ce{BiH3}$ the bond angles are very
  close to $90^\circ$.

I couldn't make much sense out of the above rule. My questions are as follows:

What does the following part mean?

  according to hybridization, $\mathrm{sp^3d = sp^2 + pd}$,
  $\mathrm{sp^3d^2 = sp + p^2d^2}$, $\mathrm{sp^3d^3 = sp + p^2d^3}$

Does it mean that the hybridized orbitals split in this way? If so, why should they split?
Why would the more electronegative atom prefer the orbital with more p character?
Even if Drago's rule holds, why is the statement in the paragraph beginning with "Also, as a result of Drago's effect when atoms …" true? I could not understand why the same won't occur for atoms with electronegativity $>2.5$.

I could not find much information regarding Drago's rule on the internet. Not even on Wikipedia. One of my acquaintances (who is a chemist) said that no such rule exists. But I didn't get much time to discuss the matter with him.

So does such a rule really exist? And, in that case, how can we answer the above two questions given as bullets  using the existing theories in chemistry?


texts: A friend of mine bought a piece of furniture that had a super smelly wood varnish, so I read around online and someone said to light candles to burn the chemical fumes.  Does anybody know if there is a chemical reaction between the wood varnish fumes and the candles? they are unscented candles and I assume they can break down the hydrocarbons in the wood varnish fumes.  Are there any other harmful chemical in the wood varnish fumes that are not oxidized by the candles that cannot be smelled by humans?


texts: Does an acetal give a positive Tollens test?

texts:
In Organic Chemistry (Wade) there is a question:

  Which of the following compounds would give a positive Tollens' test? (Remember that the Tollens' test involves mild basic aqueous conditions.)

The answers manual says this compound - $\ce{CH3-(CH2)3-CH(OCH3)2}$ - gives a negative result as it is an "acetal stable in base: no reaction"

Now, I would have thought this is positive. Earlier in the chapter it's taught that since the Tollens reagent removes any aldehyde present, even if at equilibrium the amount of aldehyde is very small, the Tollens reagent will nevertheless predominate due to Le Chatelier's principle (the small amount of aldehyde will be removed slowly but surely, until eventually all of the solution is converted to aldehyde and then to the tollens product).

In this example, whilst I respect that the acetal product may be by far the major product, surely a very, very small percentage of the acetal is nevertheless converted to the aldehyde, via protonation of a methoxy group, which leaves, and then attack by $\ce{H2O}$, followed by deprotonation of $\ce{H2O -> OH}$, and then protonation of the other methoxy group, which leaves, leaving a carbocation, which the $\ce{OH}$ attacks forming a double bond and a positive charge on the $\ce{OH}$, followed by deprotonation on the $\ce{OH}$  giving an aldehyde?

This may be unlikely, but according to Le Chatelier's principle, it just needs to occur at some small quantity in order to be continuously removed by the tollens reagent, and thus ends up predominating and removing all of the acetal product given enough time? Why is this not positive?


texts:
So I saw this problem but can't seem to figure out how to get the answer. I got a test tomorrow lol.

41) $\ce{SO2Cl2}$ decomposes in the gas phase by the following reaction:

$$\ce{SO2Cl2 -> SO2(g) + Cl2(g)}$$

The reaction is first order in $\ce{SO2Cl2}$ and the rate constant is $\ce{3.0 x 10}$^-6 at $600k$.A vessel is charged with 3.3 atm of $\ce{SO2Cl2}$ at 600k. The partial pressure of $\ce{SO2}$ at $\ce{3.0 x 10^5}$
s is ______ atm.

Answer is 2

What I tried:

Starting with PV = nRT(rearranging it to solve for m/v), and using the integrated rate law for a first order equation, I found the concentration of $\ce{Cl2}$ and $\ce{SO4}$. However, I don't know how to isolate the amount of moles to create a mole fraction.

$\ce{ln[SO2Cl2]_i = ln[SO2Cl2]_f -(3.0 * 10^{-6})(3.0 * 10^5)}$

$\ce{[SO2Cl2]_i = \frac{MP}{RT}}$

$\ce{[SO2Cl2]_i = 9.046}$

Plugging back into the first equation:

$\ce{[SO2Cl2]_f = 3.67805}$

$\ce{\frac{m_{Cl}_2 + m_{SO}_2}{V}} = 5.36849$

Not sure where to go from here...

Appreciate your help!


texts:
I'm non technical and have a question that you can hopefully help me out with as I've been searching online and so far haven't found any answered
I'm looking for a product that will thicken the following paint
polymarineshop - hypalon paint for avon inflatables
Any help at all would be greatly received
Best wishes
Ant


texts:
i am working with a multicomponent alloy system for soft magnetic application,it is iron based and have composition of Fe Mn Si B Mo,how can i calculate the net magnetic moment or saturation magnetization of the system,consider proper mixing of alloys in melt takes place.
kindly tell me the theoritical way of calculating,and individual contribution


texts: Which orbital in a subshell gets filled first?

texts: Let's say we're filling electrons in subshell 2p. This subshell will have $m_l = -1$, $m_l = 0$, and $m_l = 1$ orbitals. Does the 'filling' of electrons depend on the value of $m_l$? Meaning, does the value of $m_l$ determine if it gets filled first by an electron or not?


texts:
I'm familiar with infrared spectroscopy generally, which probes mainly the vibrational behavior of molecules under study.  However, I'm seeing references in various literature to 'infrared action spectroscopy' (e.g., here), which I'm having a hard time finding information about.

So, the title question: What is the difference between infrared action spectroscopy and conventional IR spectroscopy?


texts: Why is Potassium in French and English not called Kalium?

texts: The symbol from the periodic table for Potassium is "K". This fits my native language (dutch), where Potassium is called "Kalium". The same question applies to Sodium (Na), which again in Dutch is called "Natrium". A quick look at Wikipedia showed that Potassium is mainly used as a word in Roman based languages (French, Spanish) and to my surprise in English. What is the history behind this?


texts:
Are (cyclic) $\ce{C}$-chain molecules as in the picture likely to occur or do they exist at all?

 and so on...

EDIT:

I'm considering only double bonds between $\ce{C}$ atoms. This rules out most common allotropes.


texts: How to determine the pressure to output a gas to achieve a particular gas flow rate?

texts: I have a 420-liter (14.9 cubic ft) helium cylinder and a pressure regulator with a gauge supporting up to 160 psi. My requirement is to ensure a flow of 10 to 15 liters / min. How do I determine the pressure setting on my pressure regulator to fulfill my flow rate requirement?


texts: What is the difference between the KLMN and SPDF methods of finding electronic configuration?

texts: I've always been puzzled by this because my teachers happen to use only the KLMN method, but what is the difference between the KLMN and SPDF methods of finding electronic configuration?


texts:
Are the height of the Cubic Close packing Lattice and the cubic Hexagonal Close Packing the same?
My understanding says that these unit cells are formed by different arrangement of atoms, ABC for CCP and ABAB for HCP and because they are made from two different layers their heights should be different, is it so? And if it is, how do I calculate the Height of a CCP lattice?
(I know how to calculate height for cubic HCP.)


texts:
I bought a 2 pH meters several months back from Amazon for roughly $10 a piece.  I couldn't tell you how they work, but here's the link on Amazon:  http://www.amazon.com/gp/product/B0087LOWIA/ref=wms_ohs_product?ie=UTF8&psc=1

I also got a neutral buffer solution for calibration.  It worked fine initially but I'm thinking it's off.  It's now being used for pH testing in the salt water of an floatation tank (147 gallons of water + 750 lbs pharmaceutical grade epsom salts and 50 pounds of dead sea salt).  One meter shows a pH of 6 and another of the same kind at about 8.

My question is, does the salt effect the accuracy of the meter?  Are the meters inherently bad, or do they need periodic recalibration?  I didn't want to keep buying litmus paper.


texts: Why do transition elements make colored compounds?

texts: Why do transition metals element  make colored compounds both in solid form and in solution? Is it related to their electrons?


texts: Why is the para position preferred more than ortho in the electrophilic substitution reactions of haloarenes?


texts: Does the octet rule only apply to the second and third shell or does it apply further?

texts:
In my textbook, examples for the octet rule are only given for up to the third shell.
What about the fourth and fifth shell?
I still get confused over the fact that the $n=3$ shell has 18 electrons yet for chemical purposes atoms seek out 8 electrons. My understanding is that the energy difference between the 3p and 3d orbitals are just so large that it creates a certain stability when the 3p orbital is full. If that is true then things should get messier for the fourth and fifth shells due to more overlapping.
The first shell contains the 1s orbitals. The second shell the 2s and 2p. The third shell the 3s and 3p. What orbitals do the fourth and fifth shells include and how many electrons fill these shells?
Another way of viewing my issue. Take the electronic configuration of Calcium which is 2,8,8,2. There are 2 electrons in the fourth shell. What is the maximum number that can go in that fourth shell before a fifth shell is introduced?


texts: Why are 7-membered rings less likely to form than 5- and 6- membered rings?

texts:
I see 5- and 6-membered ring products as the major products even when 7-membered rings are possible. Why is that 5- and 6-membered rings are more likely to form than 7-membered rings? Is it even true?

My textbook says a 5-membered ring is the major product and the 7-membered ring is the minor product in intra-molecular aldol condensation reaction of 6-oxoheptanal.

Major Product: 1-(cyclopent-1-en-1-yl)propan-2-one
Minor Product: cyclohept-2-ene-1-carbaldehyde and 2-methylcyclopent-1-ene-1-carbaldehyde

This is not the only reaction where I found a 5-membered ring as a major product when a 7-membered ring was possible.


texts:
What is the density of LPG (in vapour state) in g/L?
Please note that I'm asking about the density of vapour LPG when it comes out of the cylinder. NOT the liquefied density!


texts: The IUPAC name of chlordiazepoxide is given as : 7-chloro-2-methylamino-5-phenyl-3H-1,4-benzodiazepine-4-oxide, but when I started numbering the structure, I am unable to find chlorine on 7th carbon, it is on 10th. Then why 7-chloro... is given is it wrong? Or I am wrong? Please help by numbering the structure in a diagram even on a paper an upload the photo.


texts: What else other than zinc can reduce Cr(III) to Cr(II)?

texts:
I successfully completed the synthesis of bis(chromium(II)hydrate)tetraacetate (aka chromous acetate) using zinc as the reducing agent. For my lab report, I was asked to suggest at least two other reagents which may used in place of elemental zinc in the synthesis of Cr2(H2O)2(u-OAc)4.

Would magnesium metal and manganese metal work since both their standard reduction potentials are more negative than Zn(s)?
And why does zinc make the more practical choice?

I couldnt find ANY literature showing this synthesis using any other reducing agent other than zinc...


texts:
I'd like some help in constructing the IUPAC name of aspartame:

From what I understand there are carboxylic acid, amine, amide, ester, and phenyl groups - but I'm having trouble figuring out the order in which to name them.


texts: How to calculate whether a redox reaction is spontanuous?

texts:
I have some difficulties to apply the basic concepts of calculating whether a reaction is spontanuous or not.

given:

$$\ce{H_2SO_3(aq) + 2Mn(s) +4H^+(aq) -> S(s) + 2Mn^{2+}(aq) +3H_2 O(l)}$$

and those tables containing the stadnard reduction potentials:

The formula to apply is the following: $E_{cell} = E(reduction)_{cathode} - E(oxidation)_{anode} $

$E_{cell} = 0.20 - (+1.23)$
$E_{cell} = -1.03$

The answer is that the reaction occurs sopontaniously. However this is not what I calculated, according to my calculations it doesn't. What am I doing wrong?


texts:
As depicted in books, $\ce{NO3-}$ and $\ce{NO2-}$ are called as nitrate and nitrite respectively. Where (-ate) suffix is used for higher oxidation state and (-ite) suffix is used for lower oxidation state (just like:- sulfate and sulfite).

Now since Nitrogen is 2nd period element, hence it can't expand it's octet (no vacant d-orbital). So I didn't get how (-ite or -ate) suffix can be used if nitrogen shows only 1 stable oxidation state i.e; (+3). Can anyone suggest?


texts: In (1R,2S)-2-(hydroxymethyl)cyclohexan-1-ol shown below, Ha and Hb are diastereotopic (they will have different chemical shifts), but because of fast rotation, NOESY should show that both couple with Hc, right? How to differentiate diastereotopic protons by NMR in flexible groups?


texts: When is equilibrium analysis appropriate?

texts: What is a good rule of thumb to use to determine if equilibrium is the appropriate assumption?  I assume it is mainly to do with the time scales of the problem, meaning if the reaction time scales are very short, we could probably assume that we get to equilibrium very quickly.  Is there an accepted metric for determining if the equilibrium assumption is valid?


texts:
My book States part C as the answer of the following question.

But according to me, part D, that is soda lime decarboxylation can also be a perfect answer besides the Corey House synthesis( that is the part C )the answer given by my book.
Please help in clearing my misconceptions.


texts: Benzene from cyclopropane-1,2,3-triyltrimethanol in acidic medium

texts:
What is the mechanism of this reaction? After performing $\ce{E1}$ thrice I was expecting 1,2,3-trimethylidenecyclopropane to be formed instead.

I know it's highly strained but I couldn't adopt any other pathway to reach any other product.

Is the triene product not formed at all? If cyclopropane-1,2,3-trione can exist I think even the triene product can.

This reaction is from my exercise book, couldn't find it on orgsyn.org.


texts:
I am trying to build a solid-liquid interface to be simulate using molecular dynamics. Since, I would be using ab initio molecular dynamics (cpmd or cp2k), I need the minimum cell dimensions. Please suggest some ways to fix the cell dimensions.

The issues that I am concerned about are given in for example in the science paper (http://science.sciencemag.org/content/303/5658/658.full). It is said that there should be a minimum size of the system (specially in the direction perpendicular to the slab) to attain trustworthy results. I am not able to find how and why? For example, if I take 3-10 layers of atoms for making the surface how to determine which one would yield the trustworthy results?


texts: Ionizing radiation and oxidation without oxidizing agents

texts:
My knowledge on this subject is a bit rusty, so excuse me if I'm asking the wrong question here. I was taking a look at my high school chemistry books from many years ago, and I noticed that reduction and oxidation reactions take part together; meaning that you can't have oxidation without an oxidizing agent.

My question is, that if we have a source of radiation, that emits alpha particles, which attract electrons, or beta particles which repel them, or a source of powerful electromagnetic radiation like gamma radiation, that can knock electrons off of atoms, and we bombard some gas with radiation, ionizing it, then would it count as oxidation without reduction? What exactly is going on redox-wise? We would have positive ions, but no oxidizing agent, or would we?


texts:
A full FAQ post has been written on meta.chem.SE, explaining the premise of synthesis golf and the 'rules'. Please take a look at this before answering (if you haven't already).

The target of this Easter special round of synthesis golf is tezacaptor, which has recently been approved by the FDA as a treatment for cystic fibrosis in combination with ivacaftor:

InChI=1S/C26H28F2N2O6/c1-24(2,14-32)22-10-15-9-17(4-5-19(15)30(22)12-18(33)13-31)29-23(34)25(7-8-25)16-3-6-20-21(11-16)36-26(27,28)35-20/h3-6,9-11,18,31-33H,7-8,12-14H2,1-2H3,(H,29,34)/t18-/m1/s1

Any commercial starting material is acceptable (as previously, commercial meaning you can buy it from Sigma-Aldrich) providing it has 10 or fewer carbons
The synthesis must include a cyclopropanation (i.e. the starting materials cannot contain a cyclopropane)
The synthesis should ideally provide a single stereoisomer of the hydroxyl stereo centre, but to keep things more accessible, a racemic synthesis won't be criticised


texts:
Copper nitrate, calcium carbonate and ammonium chloride mixed will patina copper green. I need to know

If calcium carbonate should be a heavy powder or a reagent.
If calcium chloride is a dehydrate or reagent.
If ammonium chloride should be granular or granular reagent.

These mix with water in equal parts. I`m not a chemist, and this is for a sculpture with a recipe from an old metal techniques book.


texts: Materials used in cooktop heating element, and reason for black appearance

texts:
I have been interested in the structure of heating elements/coils used in cooktops. I am referring to something such as in the following picture:

I have a cooktop at home with such elements, and at parts where there was more scraping, I can see a silver-ish colour rather than the black, suggesting the black material is a thin layer around some metal resembling stainless steel, in appearance at least.

I have read on Wikipedia that often such heating elements would have an outer layer made "of stainless steel alloys, such as Incoloy, or copper" (and similar statements elsewhere). This seems to suggest that the silver-ish layer I have seen at the scraped parts in my cooktop is indeed stainless steel.
What I am interested in is what the black layer is.
My question is why these heating elements appear black in appearance; what the black layer is.

I have a possible guess, which I would also be interested to affirm or negate with you, which is that this is due to oxidation of the metals, which perhaps is done by the manufacturer(s) in advance because they expect that the high temperature that the metal would get to during cooking would itself speed up  oxidation and the resulting discoloration, and doing the oxidation in advance (and in a controlled manner which does that uniformly, so the colour seems uniform) prevents that from happening by forming a protective layer of oxidised metal. One reason I am guessing that, is that I looked on Wikipedia at possible oxides of iron, chromium, and nickel, and all of these seem to have at least one oxide with a black appearance. Iron for example has $\ce{FeO}$ and $\ce{Fe3O4}$.


texts: Rearrangement with sodium iodide (ring opening)

texts:
I'm not able to figure out the mechanism for this reaction. I don't see how sodium iodide in acetone could lead to rearrangement, and surprisingly ring opening!

What is this reaction called, if it has a special name? How does it occur?

P.S. In general, as far as I know, sodium iodide in acetone promotes excellent SN2 substitution, so all bromine atoms should be replaced by iodine. After this, because 1,2-diodo compounds (vicinal di-iodides) are unstable, elimination takes place (removal of iodine) and formation of alkene occurs (that's what I've seen happen, usually).


texts: Is it possible that blowing on water (hot/cold) can cause a reaction between the $\ce{CO2}$ from expiration and the water, to form $\ce{H2CO3}$? Is $\ce{H2CO3}$ dangerous?


texts: What is it that is "symmetry-adapted" about symmetry-adapted perturbation theory?

texts:
I think this is a fairly straightforward question which I should know the answer to, but surprisingly cannot find a discussion of online.

Symmetry-adapted perturbation theory (SAPT) is a fairly common method to describe intermolecular interactions using physically meaningful terms (electrostatics, exchange, induction, dispersion), where the interaction is built up. That is, SAPT calculates the interactions directly as opposed to finding the interaction strength by subtraction.

So, quite simply, in SAPT, what does the "symmetry-adapted" specifically mean, and why is it necessary to specify this?

In other words, is there a non-symmetry-adapted perturbation theory which can be used for intermolecular interactions?

Finally, how, if at all, does this symmetry-adaptation relate to the kind we use when constructing molecular orbitals using group theory?


texts: Why is potassium permanganate(VII) such a strong oxidising agent, why does its behaviour depend on pH of the solution it is present in?

texts:
Why is potassium permanganate such a strong oxidizing agent? Let is say we have a $\ce{KMnO4}$ aqueous solution which is acidified by adding sulfuric acid. What is going on in the solution which makes it so oxidizing that immediately if we add an organic or inorganic molecule it gets immediately oxidized?

Also why under different pH potassium permanganate behaves differently i.e. Mn reduces from +7 to +2 in acidic conditions whereas it goes to +4 in neutral conditions?


texts: What pH indicators are commonly used for non-polar medium?

texts:
Compounds, commonly used as pH-indicators, are soluble in aqueous media and polar solvents (DMSO, DMF, NMP etc.) and are functional pretty much across all these solvents. However, practically none these indicators are soluble in non-polar solvents (hexane, chloroform, dioxane etc.).

I briefly searched for the suitable available systems and so far there is only an article about oxoporphyrinogen derivatives used as pH-indicators in $\ce{CH2Cl2}$ [1]. Are there any other common substances that are typically used for the visualization of acid-base equilibrium in solvents with low polarity?

Reference

Shundo, A.; Ishihara, S.; Labuta, J.; Onuma, Y.; Sakai, H.; Abe, M.; Ariga, K.; Hill, J. P. Chem. Commun. 2013, 49 (61), 6870–6872. DOI: 10.1039/C3CC42859A.


texts: how to determine range potential of Pb in cyclic voltammetry?

texts: standart potential of $\ce{Pb}$ is -0.13 V. how we determine an optimum potential of $\ce{Pb}$ sample? and how we choose the range potential?


texts: Why do we integrate square of wave function over N-1 electron coordinates?

texts:
Quote form F.Jensen's Introduction to computational chemistry:

"The electron density is the square of the wavefunction, integrated over N-1 electron coordinates..."

Why do we integrate over N-1 instead of N electorn coordinates?
What would happen if we integrated over N coordinates?
I suppose we would get a norm if we integrated over N coordinates, or 1 if wavefunction is normed.
But why N-1?


texts: What do the six polymorphs of chocolate look like?

texts:
Today I learnt that chocolate tempering works by controlling the temperature to ensure the crystals set to one (type V) of the six polymorphs.

What do these polymorphs actually look like? By that I mean: what is the crystal structure? Also, what gives type V its properties?


texts: Obtaining conformational energy from Newman projections in first place

texts: In this source, the conformational energy from Newman projections is obtained. Is there a formula or quantum chemistry approach to obtain the values in first place (pretend that I don't know the source)?


texts: how could I make a file conversion from .spc (thermo fisher) in .cdf (Shimadzu) format file?


texts: Why does charcoal not produce smoke when heated?

texts:
As I understand; the reason we have smoke in a fire is because the heat causes wood (or whatever material is burning) to dis-integrate, the disintegrated components react with oxygen to create more heat; causing a chain reaction.
Much of the smoke we see is the dis-integrated carbon in the air from incomplete combustion.
However, when we heat charcoal in a vacuum, there is no smoke. But if heat is what causes carbon to dis-integrate, then why does heating carbon (regardless of oxygen presence) not cause smoke?


texts: A glass of water with ice-cubes in it. Where's the water the coldest; at the top or bottom?

texts:
Suppose that I fill a glass with ice water.  As the ice melts, it cools the water around it.  Given that cold water is denser than hot water, I would presume that the cold water would sink to the bottom … but it would warm as it sinks, reducing the density.  Meanwhile, the ice is still melting and giving off its cold to the surrounding water.

So is drinking ice water with a straw going to get you cooler or warmer water than drinking from the lip of the glass?


texts: Mechanism of Fritsch–Buttenberg–Wiechell rearrangement

texts:
The following reaction was given, which uses potassium t-butoxide.

The solution to this problem was given as follows:

Step 1 is the attack of strong base, t-butoxide, on the vinyl proton.

Step 2 seems to have the chlorophenyl group shift to the neighbouring carbon, forcing the cleavage of the $\ce{C–Br}$ bond.

Here, the bromine is conjugated to the alkene, since the lone pair on bromine is in resonance with the alkene, leading to partial double bond character between $\ce{C}$ and $\ce{Br}$. In such a case, the $\ce{C–Br}$ bond usually cannot be cleaved.

My question is

Is this carbanion intermediate responsible for the product?
What is the mechanism to form 1-chloro-4-(phenylethynyl)benzene?


texts: Mixing water and oil in microgravity outside of a container

texts:
What would happen if I  where to mix water and oil in a vacuum in microgravity  where the temperatures  were low enough so that the oil and water remain liquids also, the mixture is not inside of a container.
 I would expect the water and oil two separate into two blobs, but wouldn't the London dispersion forces hold the two blobs together?


texts:
When sulfuric acid  reacts with copper, then $\ce{H2SO4}$ gives nascent oxygen $\ce{[O]}$. The reaction is:
$$\ce{H2SO4 -> H2O + SO2 + [O]}$$

This nascent oxygen reacts with copper to create $\ce{CuO}$.

Therefore my question is that when copper reacts with $\ce{HCl}$ then why doesn’t $\ce{HCl}$ give nascent chlorine $\ce{[Cl]}$ so that it could react with copper and create copper(II) chloride $\ce{CuCl2}$?


texts: As we all know water is $\ce{H2O}$, it does not contain sodium chloride. The ocean is a solution composed of water and a solute which is salt. I was wondering how the massive amounts of $\ce{H2O}$ in our oceans first mixed with salt? I'm sure the water didn't contain salt when it first got to the oceans so how did it get mixed with salt? Thanks.


texts: "Middle row anomaly" of the periodic table

texts:
I was studying about the periodic table recently, and was reading a topic associated with oxides of halogens, and came across the following line

  The bromine oxides, $\ce{Br2O}$, $\ce{BrO2}$, $\ce{BrO3}$ are the least stable halogen oxides (Middle row anomaly) and exist only at low temperatures. They are very powerful oxidizing agents.

So, I went to search this on Google, and found these lines

  It refers to the instability of oxides of bromine as compared to relative stability of oxides of chlorine and Iodine at room temperature, the former being stable only at low temperatures.

But the line above is simply restating what the book had already told.
So, is their any specific reason why this happens, or is this only due to the experimental data we have gathered?


texts: Calculation of overall rate constant of a parallel reaction

texts:
Consider a parallel reaction

$\ce{A->B}$ (rate constant for this reaction is $k_1$ and it follows first order kinectics),

$\ce{2A->C}$ (rate constant for this reaction is $k_2$ and it follows first order kinetics).

Then we can write
$$\mathrm dA/\mathrm dt = \mathrm dA_1/\mathrm dt + \mathrm dA_2/\mathrm dt$$
(where $\mathrm dA_1$ is the amount of $\ce A$ going through the first path and $\mathrm dA_2$ is the amoubt of $\ce A$ going through 2nd path),

$$\mathrm dA/\mathrm dt = k_1[\ce A] + 2k_2[\ce A]$$

Then to calculate the $k$ where $k$ is the rate constant for the overall reaction we write

$$k[\ce A] = k_1[\ce A] + 2k_2[\ce A]\tag i$$

And so $k$ comes out to be $k_1+2k_2$.

My doubt is that to write $-\mathrm d[\ce A]/\mathrm dt = k[\ce A]$ did we assume that in the overall reaction the coefficient of $\ce A$ in the overall reaction to be 1.

Taking a general case
$$\ce{$a$A->products}$$
we can write
$$-\mathrm d[\ce A]/\mathrm dt=ak[\ce A]$$

But according to the equation $\text{(i)}$ we took $a=1$. Why?

If suppose $\ce A$ is a radioactive substance and we have to calculate the mean life of $\ce A$ then we require to know the overall rate constant, so foe that what should be the value of $a$?


texts: What is responsible for the smell of incomplete hydrocarbon burning and what sensor can detect it?

texts:
After I pass the smoke from partially burned fuel oil through a filter, I can still very strongly detect the smell. It is the same thing you smell from the exhaust when an old car or truck goes by.

Even though I can easily smell it with my nose, none of my sensors can detect it. I've tried $\ce{VOC}$, $\ce{O3}$, $\ce{PM_{2.5}}$, $\ce{CO}$, $\ce{NO2}$, & combustible gas detectors and all come up clear on the filtered exhaust.

So what is left in this gas that is responsible for this strong smell (and the resulting headache) and what sensors can I use to detect it?


texts: How did they assign absolute configuration to these cis and trans 2-methylcyclohexanols?

texts:
From [1, p. 56]:this is the 4/B rule I was talking about
This is how I practiced. In the textbook, the absolute configuration of one of the enantiomers (I am referring to the the first compound) is written as 1R,2S. But when I tried to redo it, I arrived at 1R,2R. I didn't understand where I went wrong. I think the way I am visualising the compound is not correct.

4.3.5 Nomenclature of polysubstituted cyclanes
Polysubstituted cyclanes, e.g., cyclopentanes, cyclohexanes etc. exist in a number of stereoisomers (diastereomers and enantiomers) depending on the number and nature of the substituents. The disubstituted cyclanes give two diastereomers which can be conveniently and unambiguously described as cis and trans isomers, e.g., cis- and trans-2-methylcyclohexanols (XXVII) and (XXVIII) (Figure 4.13). Each of the diastereomers in turn gives two enantiomers which can be named, following the R, S nomenclature, as R, S and S, R for the cis and S, S and R, R for the trans isomer (use 4/B rule) as shown in the Figure.

Figure 4.13 Disubstituted cyclohexanes

When I practice on this picture I always arrive at the same configuration both on C1 and C2. Am I assigning the priorities in a wrong way?
Reference

Nasipuri, D. Stereochemistry of Organic Compounds: Principles and Applications; New Age International, 1994. ISBN 978-81-224-0570-5. (Google Books)


texts: If I want to sample rate constants of chemical reactions, what the distribution will be appropriate?

texts: For example, I have a (chemical) reaction systems, I want to sample the parameter space. What will be the best and validated distribution for sampling? And why?


texts: I know there are ionic bonds in solid NaCl. But what bonds are present in liquid (molten) NaCl? I believe there should be some kind of attraction there, because particles (ions) are pretty close to each other. What are these attractions?


texts:
What is the correct name for a reaction like this?

$$ \ce{ 4MnO2 ->[500\ ^\circ \text{C}] 2Mn2O3 + O2 ^}$$

Is it a synthesis, or a Decomposition?
I tried to find it out with http://en.wikipedia.org/wiki/Chemical_reaction but i did not get the link between the formula and the nomenclature as it seems to be both.


texts: Why does the image of cyclo[18]carbon look like a nonagon?

texts:
The $\ce{C18}$ allotrope cyclocarbon has been synthesized and imaged.[1] Science has most details behind a paywall, but this discussion includes an image:

In this octakaidecagonal molecule, each $\ce{\color{blue}{C}}$ is bonded viz. $\ce{C-\color{blue}{C}#C}$. Yet the above image looks like a nonagon. Why does every other carbon atom stand out as an obvious vertex while the others don't? My thoughts:

The internal angles are close to $180^\circ$, making vertices hard to see. However, I wouldn't expect the internal angles of this octakaidecagon to differ much.
I wonder if this molecule has a delocalised ring analogous to the one in benzene. On this idea, each of the nine visible edges could alternate between the states $\ce{C-C#C}$, $\ce{C#C-C}$. But this wouldn't explain why "odd" vertices have one appearance while "even" ones have another. I'm not convinced of this idea anyway, because it would average out to $\ce{C=C=C}$, unlike the $1.5$-bonds in benzene.

References:

Kaiser, K.; Scriven, L. M.; Schulz, F.; Gawel, P.; Gross, L.; Anderson, H. L. An sp-hybridized molecular carbon allotrope, cyclo[18]carbon. Science 2019, eaay1914. DOI: 10.1126/science.aay1914.


texts: Will hydrogen chloride dissolved in ethanol react with magnesium?

texts:
Magnesium will react with aqueous HCl to form magnesium chloride and hydrogen gas. Simple. But I've just read in my textbook that HCl in a solution of ethanol no reaction will take place. There is no explanation given.

I know HCl is soluble in both solutions, but I cannot figure out what accounts for the difference in reactivity with Mg. I suppose it must be due to waters ability to act as a Bronsted-Lowry base and form a hydronium ion, but I also can't see how this would be an effective intermediate in the reaction mechanism.
I am lost, and would appreciate any expertise in this area.


texts: What fraction of air gets expelled upon heating an empty flask?

texts:
A student forgot to add the reaction mixture to the round bottomed flask at $\pu{27 ^\circ C}$ but instead he placed the flask on the flame. After a lapse of time he realised his mistake and using a pyrometer, he found the temperature of the flask was $\pu{477 ^\circ C}$. What fraction of air would have been expelled out?

By solving $$\frac{V_1}{V_1 + V_2} = \frac{T_1}{T_2}$$ I found $$\frac{V_2}{V_1} = \frac{3}{2}.$$ But according to my book it is $\frac 35$. What exactly is this ratio?