texts: Why are the secondary alpha hydrogens more acidic than primary alpha hydrogens (keto-enol tautomerization)?

texts:
I learned in organic chemistry that secondary/tertiary carbanions are less stable than primary carbanions and therefore primary hydrogens are MORE acidic than secondary/tertiary hydrogens.

But lets take 3-methyl-2-butanone as an example. It seems that the more substituted alpha carbon is more acidic than the nearby primary carbon. In other words, it seems that the keto-enol tautomerization prefers to form a C=C with the secondary carbon over the primary carbon.

Why would a base prefer to deprotonate the secondary carbon over the primary carbon to trigger keto-enol tautomerization over the theoretically more acidic primary carbon?


texts: Tool that generates electrostatic maps of molecules?

texts: Do you know any tools that generate electrostatic potential 2d maps of the molecules as an image?


texts: Carbocation stability + determining position of attack on a carbocation in SN1 reaction

texts:
It's implied that the right structure is the more stable carbocation because it undergoes the second half of an SN1 reaction, but I'm not entirely sure why:

I'm also not sure why the $\ce{MeOH}$ attacks the carbon next to the carbocation and not the oxygen itself, where it has the positive charge (doesn't the nucleophile attack the carbocation, or whichever atom bears the positive charge?)


texts: Can the electrolytes be in gaseous state?

texts:
Possible Duplicate:
  Will gaseous ionic compounds be free moving ions?

I know it sounds extremely expensive, but what if we could heat the ionic compound to evaporate it and achieve the lattice energy and break them into free ions, wouldn't the electrolysis be faster, as the ions can move faster freely than in liquid state?


texts: Drug design methods - docking software, binding affinity

texts:
Lately I've seen videos and some articles explaining drug design. I would also like to specifically cite this guy, who isn't the most credible guy in the planet, but some of the stuff in the video makes sense to some degree, and he just confused me further.

Now I work on a completely different field on my day job, but I would like to ask a few questions, out of curiosity, because the techniques described in the video really piqued my interest.

Is it the case that when designing drugs (i.e. these proteins) we attempt to optimise binding affinity (maximise?)
How well does Autodock Vina compute this affinity? Is it opinionated? I've seen a few docking software, it looks like there are different methods to compute docking score? (can you recommend further reading for me in this regard)
Is there a linear correlation between binding affinity and drug efficacy? I.e. does it mean that higher binding affinity directly means we have a better drug, or is there some sweet point kinda thing?
Why can't we use very complex molecules, more than 300 characters in SMILES length to combat viruses for example? I noticed everyone was trying to minimise ligands?
How can software like AutoDock tools prepare your proteins for docking, is there a standard method (they add hydrogens, add Gasteiger charges). Is that guaranteed to be accurate in every case?

To clarify, I'm not looking for detailed answers, since I am completely off the domain, I just want to have a basic idea for these questions, and perhaps recommendations on further reading from you guys.

Thank you, and stay strong!


texts: How does the addition of NaCl to the cathode side effect the potential of a voltaic cell: Zn(s) | Zn2+(aq) 0.1M || Cu2+(aq) 0.1M | Cu(s)

texts:
By addition of $\ce{NaCl}$ to the $\ce{Zn}$ side of the cell, I observed precipitation of $\ce{ZnCl2}$.
I measured the voltage to $\pu{1.05 V}$ before adding $\ce{NaCl}$ to the cathode side, I then observed the voltage go down by addition of the salt.
According to the Nernst equation: as the $\ce{Zn^2+}$ ion concentration reduces with precipitation, there should be an increase in voltage.
$$E = 1.05 - \frac{RT}{nF} \ln Q$$
$$E= 1.05 - \frac{RT}{nF} \ln \left(\frac{[\ce{Zn^2+}]}{[\ce{Cu^2+}]}\right)$$
since $\ln Q \lt 0$ for $[\ce{Zn^2+}] < [\ce{Cu^2+}]$
"$-\frac{RT}{nF} \ln Q$" term would be positive. Therefore the voltage should go up. But the opposite was observed and I don't know how to explain it.


texts: Is adding the word "solution" necessary when listing the materials used in a synthesis?

texts:
I am editing a chemistry-related paper and the synthesis procedure described is as follows:

  Then, 10 mL of the intermediate were mixed with 10 mL of 1% (w/v)
  VCPL and 2 mL of 0.1% (w/v) KPS.

I was wondering if one should add the word "solution" after the name of the ingredients as follows:

  Then, 10 mL of the intermediate were mixed with 15 mL of a 2% (w/v)
  VCPL solution and 3 mL of a 0.2% (w/v) KPT solution.

I think that indicating a volume and a % (w/v) gives it away that you are referring to a solution containing the active ingredient, but should the word "solution" still be added?

Thanks.


texts: Difference between thermal reactions and photochemical reactions

texts:
In a photochemical reaction, everything starts with absorption of a photon. I.e. a ground state reactant is excited to the first excited state. Sometimes the reaction barrier on the ground state surface is too high; perhaps lower barriers exist in other dimensions that lead to undesirable products or dissociation. Perhaps the relevant barrier is much lower on the excited state surface, which makes the reaction possible in the excited state.

Is the difference, then, that thermal reactions take place exclusively on the ground state surface, while a photochemical reaction takes place, at least in part, on the excited state surface?


texts:
Help me please with a question about carbon-based life development. I'm almost sure I know answer, could anybody with more solid knowledge in the area confirm it. Could carbon-based life develop on a planet without helium? Did helium help the process on any stage?

As I understand, yes could, because helium is noble gas which does not react with other elements. Or maybe I am wrong?


texts: How do I prepare citric acid solution (from anhydrous powder) of accurate concentration, given that the solution volume expands when water is added?

texts:
I attempted to prepare saturated citric acid solution from anhydrous powder. According to online data, the solubility limit was 59.2 w/w at 20 °C, i.e. 59.2 g citric acid in 100 mL water. To ensure full saturation (as in the case of preparing brine solution), I ended up weighing 67 g of the powder and tried adding 100 mL of water to it.
However, when I had added about 67 mL of water, the 100 mL Schott bottle was already full, and all of the powder dissolved (estimated 5.22 M solution). Since there is an apparent volume expansion, how then should this solution (or a citric acid solution of any other desired concentration) be prepared?


texts: Can hydrogen and oxygen gasses be turned back into water?

texts: I electrolized water today, and got hydrogen. And I have a bottle of oxygen. Can I combine those to get myself water? I know $\ce{H2O}$ is super pure water, but I just want to try. Is this too idiotic to ask or can it be done?


texts: Caclulating the Solubility of Fluorite in River Water

texts:
Source: Chapter 4 of Brunlow's 1979 Geochemistry text.

  Calculate the solubility of fluorite in river water with the average composition given in table 4-1.  Assume that no fluoride complexes form.

Table 4-1 lists ppm, mEq/L and moles/L values for constituents, anions and cations found in the water sample.  There is no value for $\ce{F}^-$ but there is for $\ce{Ca}^{2+}$. The molarity of $\ce{Ca^{2+}}$ is given to be $\pu{0.375E-3M}$

My attempt::

$$\ce{CaF2 -> Ca^{2+} + 2Fl^{-}}$$

$K_\mathrm {sp}$ of $\ce{CaF2}$= $10^{-10.5}$ (from a table in the book)

$K_\mathrm{sp} = [\ce{Ca_{\text{original}}} + \ce{Ca_{\text{added}}}][\ce{F_{\text{added}}}]^2$

$[\ce{F_{\text{added}}}] = [2\ce{Ca_{\text{added}}}]$

$K_\mathrm{sp} = [\ce{Ca_{\text{original}}} + \ce{Ca_{\text{added}}}][2\ce{Ca_{\text{added}}}]^2 = 4[\ce{Ca_{\text{original}}} + \ce{Ca_{\text{added}}}][\ce{Ca_{\text{added}}}]^2$

Am I on the right track?  I end up with a polynomial to solve for.  The answer in the back of the book is $10^{-4.64}$ which I can't arrive at.

The other method I've tried is to calculate the ppm of fluorite dissolved in pure water ($\pu{15.6ppm}$) and then subtract the ppm value for the river water $\ce{Ca^{2+}}$ given in the table ($\pu{15.0ppm}$) and then convert the result ($\pu{0.6ppm}$) to $\pu{7.69e-6 moles/L}$ which doesn't equal the answer in the back of the book ($10^{-4.64}$), so I believe that I'm missing something conceptually.


texts:
As the compound potassium chlorate exists, is there something as $\ce{KFO3}$?
All the other halogenates are mentioned somewhere on the web but what about this?
If no, then why?


texts: R and T conformations in relation to Activators and Inhibitors; Km of reaction in relation to uncompetitive and non-competitive inhibitor

texts:
Do

-Activators

-Competitive Inhibitors

-Non-Competitive Inhibitors

-Uncompetitive Inhibitors

all change the conformation of the targeted enzyme from T to R (activator), and from R to T (the rest) respectively?

Also, why does the Km of a reaction decrease with an uncompetitive inhibitor, while remaining constant with a non-competitive inhibitor?

I have tried to find a coherent answer to this all across the internet, but to no avail. Many thanks!


texts: 1-5 dicarboxylic acid to lactone with SOCl2?

texts:
I came across a reaction whereby a 1-5 dicarboxylic acid is converted to lactone with $\ce{SOCl2}$. I was wondering what the mechanism of this was.

I know that $\ce{SOCl2}$ converts carboxylic acids to acyl chlorides. Is it the case that one carboxylic acid undergoes this transformation, then the oxygen from the $\ce{OH}$ of the other carboxylic acid attacks the acyl chloride, making the $\ce{Cl}$ a leaving group?

Is this the case or am I missing something?


texts: What metals have been used in photography?

texts: I'm interested in knowing about the various processes that have been used in chemical photography. As I understand it, most are based on silver. Are there any major ones which have not used silver? What other metals have been used? Are there any processes which don't use metals at all?


texts: Does the volume of solution increase during a neutralisation reaction?

texts:
Say I mixed together 20 mL of HCl solution with 20 mL of NaOH solution.

$$\ce{HCl (aq) + NaOH (aq) -> NaCl + H2O}$$

Strictly speaking, would the water produced from the neutralisation process cause the volume of the overall mixture to slightly increase? So, would the volume of the final mixture (strictly speaking) be 40 mL + the volume of water produced from the reaction?


texts:
What are the products of partial hydrolysis of $\ce{XeF_6}$?
Is $\ce{XeOF_4}$ formed or $\ce{XeO_2F_2}$ is formed?


texts: How can I determine the electrode potential of ethanoic acid redox reaction?

texts:
I'm conducting a research paper on the effect of surface area ratio from anode to cathode and the electrode material on the rate of electrolysis of ethanoic acid by measuring the volume of carbon dioxide collected. In order to determine the material that I am using (so that it is kept constant), I need to determine the electrode potential of ethanoic acid.

If anyone knows of a standard electrode potential for ethanoic acid, that would be great so that I can avoid testing for it experimentally.


texts: Why do the melting and boiling points of the noble gases increase when the atomic number increases?

texts: What causes the melting and boiling points of noble gases to rise when the atomic number increases? What role do the valence electrons play in this?


texts: What is the basic concept of positive and negative charge of an atom?

texts:
In ionic compounds, e.g. NaCl, chlorine 'steals' one electron from sodium. Because of this, sodium's proton number is increased by one, and the number of electrons in chlorine is increased by one. This makes sodium positively charged and chlorine negatively charged; opposite charges makes them attract to each other.

My question is that the nucleus of the sodium ion is still surrounded by electrons, and so does the nucleus of chlorine. Do those electrons repel, even though we say opposite charges attract? What do the electrons do while they attract?


texts: My favorite groups of shapes are cupolas. Are there hydrocarbons in the shape of these similar to how cubane is to a cube? If so how stable are they, and could you please give some general information about each one.


texts:
Changing one atropisomer to another requires bond breaking (in some cases the removal and reattachement of steric groups, according to my understanding) so how it is possible that according to IUPAC atropisomers are classified as conformers (conformational isomers)?
According to IUPAC:

Atropisomers - A subclass of conformers which can be isolated as
separate chemical species and which arise from restricted rotation
about a single bond.
Conformers - One of a set of stereoisomers, each of which is
characterized by a conformation corresponding to a distinct potential
energy minimum.
Conformation - The spatial arrangement of the atoms affording
distinction between stereoisomers, which can be inter-converted by
rotations about formally single bonds. Some authorities extend the
term to include inversion at trigonal pyramidal centres and other
polytopal rearrangements.

This definition of "conformation" seems vague to me, but it is often said that changing one conformation to another involves no bond-breaking and changing one configuration to another requires bond-breaking. This is the difference between them.
IUPAC gives examples of atropisomerism: e.g. (E)-cyclooctene (given in Gold Book "planar chirality" entry). This definitely should involve bond-breaking. Other IUPAC examples of atropisomerism include substituted ortho-biphenyls.


texts: How does 1,3-dichloro-1,3,5-triazinane-2,4,6-trione (dichloroisocyanuric acid) generate hypochlorous acid when dissolved in water?

texts: Can someone draw the reaction that leads to the generation of HOCl when dichloroisocyanuric acid (structure shown below) is dissolved in water?


texts: What is the meaning of n in n-octane and similar compounds?

texts:
Straight-chain octane ($\ce{CH3(CH2)6CH3}$) is also called n-octane. What does the n stand for, and where did the term originate?

For reference, see the PubChem entry for octane (beside "Chemical Names:")


texts: How is hydration free energy of a solute measured experimentally?

texts:
I am reading a paper (Shirts, M. R.; and Pitera, J. W. and Swope, W. C. and Pande, V. S. J. Chem. Phys. 2003, 119, 5740-5761).  Near the beginning of the paper (page 5745), the authors state:

  Experimental free energies of hydration for weakly soluble solutes are
  determined from concentration measurements made on two phase systems,
  where one phase consists of a vapor with a partial pressure $P_s$ of
  some solute molecule of type $s$, and the other phase consists of an
  aqueous solution with a number density concentration for solute
  molecules of $\rho_s^{\ell}$.  When such a two phase system is at
  equilibrium with respect to transfer of molecules of type $s$ between
  the phases, the solvation free energy is given by $$\Delta G_{\text{solv}} = kT\ln(P_s / (\rho_s^{\ell} kT)).$$

What does this mean in practice?  For example, suppose that I would like to measure the hydration free energy $\Delta G_{\text{solv}}$ of a small molecule (e.g., the amino acid arginine).  That is to say, I would like to measure the solvation free energy of arginine in water.  (Since arginine has a charged side chain at neutral pH, I would expect $\Delta G_{\text{solv}}$ to be negative, because arginine is likely stabilized by water, which is polar.)

Does the expression for $\Delta G_{\text{solv}}$ above imply that I just need an aqueous solution of arginine?  Then would I need to somehow measure the partial vapor pressure $P_s$ of the arginine vapor which exists above the arginine aqueous solution?  How is such a partial vapor pressure vapor measurement done in practice?  Thanks for your time.


texts: What are actually the differences between Sidgwick & Powell theory and Nyholm & Gillespie Theory?

texts:
The famous VSEPR theory was proposed by first Sidgwick & Powell. It was modified then by Nyholm & Gillespie.

I was reading Inorganic Chemistry by J.D.Lee where he discusses very briefly the theory of Sidgwick & Powell; I couldn't somewhat conceive the language. So, I googled it but to my misfortune I could nowhere get more info other than this:

  The idea of a correlation between molecular geometry and number of valence electrons (both shared and unshared) was originally proposed in 1939 by Ryutaro Tsuchida in Japan, and was _independently presented in a Bakerian Lecture in 1940 by Nevil Sidgwick and Herbert Powell of the University of Oxford. In 1957, Ronald Gillespie and Ronald Sydney Nyholm of University College London refined this concept into a more detailed theory, capable of choosing between various alternative geometries [1]

Everyone would give the historical info that Sidgwick & Powell was the first to introduce the theory which was later modified to the present VSEPR theory. I don't want that!

Can anyone please help me to bring me forward the original Sidgwick-Powell theory? Also the million-euro question: What are the differences between the two theories? In another way to say: What were the modifications that Mr. Nyholm & Gillespie brought forward that "improved the original" theory?

[1]https://en.wikipedia.org/wiki/VSEPR_theory#History


texts: Elements other than carbon that can form many different compounds by bonding to themselves?

texts:
My textbook says the following:

  Unique among the elements, carbon can bond to itself to form extremely strong two-dimensional sheets, as it does in graphite, as well as buckyballs and nanotubes.

Is carbon the only element that can do this?

If not, then what are the other elements can also do this? Is there a term to describe such elements?

What is the chemical characteristic that allows this to occur?

I would greatly appreciate it if people could please take the time to clarify this.


texts:
For example, Magnesium has a higher charge density compared to Sodium, therefore its metallic lattice is stronger and it has a higher melting point. Does that mean that Magnesium has more protons and a smaller atomic radius or is it about its charge (2+), that makes its lattice stronger?

What does charge density show?


texts: What is an effective extraction solvent for removing hydrocarbons from soil (using a soxhlet extractor)?

texts: I am interested in improving the extraction efficiency of hydrocarbons from soil using a soxhlet extractor, and I would like to know what solvents might improve this extraction efficiency, and why. Currently, I am using 1:1 hexane:acetone.


texts: What is meant by pure solids or pure liquids?

texts:
In by book, under the topic Heterogeneous Equilibrium it is given

  For pure solid and pure liquid, active mass is taken to be unity, i.e., 1 as they remain constant throughout the reaction.

Could you please explain what are the pure solids and liquids being mentioned here?

I read some related answers to similar question but none addresses which compounds are pure which are not. Or, if I haven't noticed properly, kindly give me the link to clarify my doubt.


texts: Using molecular orbital for determining leaving group trend and nucleophilicity

texts:
Here is the question.

  Which one has better leaving group, cyclohexanol or cyclohexane that has $\ce{OH_{2}^{+}}$ substituent? Explain.

I know the answer is the latter because if both compounds are subjected in substitution reaction, the latter will yield a weak conjugate base ($\ce{H2O}$). There are some interesting facts from there which wants me to prove the answer with molecular orbital approach.

Here, I cite the part from it.

  The leaving group itself does play a slight role here in determining the energy of the $\unicode{x3c3}^*$ orbital and thus whether it is energetically favourable for the nucleophile to attack.

Based on the cited part, looks the orbital plays the role in nucleophilicity although the iodide example gives counterexample of nucleophilicity vs leaving group.

Does HOMO orbital play role in determining nucleophilicity? Based on molecular orbital of $\ce{OH-}$ and $\ce{H2O}$, the HOMO of $\ce{H2O}$ is higher than the former, thus is it correct to interpret $\ce{H2O}$ is more nucleophilic than $\ce{OH2+}$?
If nucleophilicity criteria is solely based on energy of HOMO orbital, is there a bound where the energy of HOMO orbital becomes electrophilic (or the LUMO orbital becomes nucleophilic)?
If leaving group is a thermodynamic factor (as noted by first source), would molecular orbital alone (including frontier molecular orbital) suffice to predict the leaving group order?
Can molecular orbital describes the iodide case (good leaving group but good nucleophile)?

The leaving group trend is supposed to be for similar weak bases (halides, $\ce{OTs}$, and $\ce{OMs}$).


texts: Why does increasing surface area of the electrode decrease resistance?

texts:
Which increases immediately if the surface area of the silver electrode is increased?

  overall cell voltage
  rate of change of $\ce{[Ag+]}$
  mass of $\ce{Cu}$ electrode
  change in ratio of electrode masses; ∆$(\frac{\text{ mass of Cu}}{\text{ mass of Ag}})$

The correct answer was (2), but I'm not sure why the reaction rate would go up if the surface area of the silver electrode increased. The rate of reaction is proportional to the current flowing through, which by Ohm's Law is $\frac{V}{R}$. This means that the resistance must have decreased if current increases. But resistance of the electrodes is only related to the length and cross sectional area. The problem does not specifically state any change in length or cross sectional area. It only says surface area, so what am I missing here?


texts: What happens if a proposed name for a new element cannot be abbreviated to a two-letter symbol?

texts:
Take the C-elements for example: C, Ca, Cd, Ce, Cf, Cl, Cm, Cn, Co, Cr, Cs, Cu.

Imagine some newly synthesized element is to be named after the University of Colorado: Coloradium. Its symbol can't be C, Co, Cl, Cr, Ca, Cd, Cu, or Cm, so we're forced to choose Ci.

Then another new element is synthesized, and it is to be named after Celine Dion: Celinium. Its symbol can't be C, Ce, Cl, Ci, Cn, Cu, or Cm. What would they choose for a symbol?


texts: Fluorometer for measuring fluorescence in a sheet of water

texts:
Does anyone know of a fluorometer that I could use to measure fluorescence in a thin sheet of water.  So it would be like holding a piece of writing or printer paper vertically and trying to get a reading of the fluorescence at various locations around an 8.5 by 11 area of the paper sheet (although the sheet of water won't be nearly that big - more like 3x5).  A small probe so that multiple locations could be measured by simply moving the probe would be great. A submersible probe would not be good as it would disrupt the sheet.  The sheet will contain quinine at varying amounts depending upon how far a quenching reaction with chloride ion has progressed.
Thanks.


texts: How does the partial pressure of gas C change with the change in volume of the container?

texts:
Suppose I have the equilibrium in a closed container:
$$\ce{3A(s) + 4B(g) -> 4C(g) + D(s)}$$

What happens to the partial pressure of C if the volume of the container is halved?

I was pondering about this question, because by the gas equilibrium constant
$$K_\mathrm{p} = \frac{[C]^4}{[B]^4}$$
 the partial pressure of each should remain equal to each other. But using an ice table, $K_\mathrm{p} = \frac{[C]+x}{[B]-x}$, or you can flip it around. Either way, $x$ should equal 0 by this equation for them to remain the same, which means that the partial pressures don't change, which then means that the gases are turning into the solids. But by the chemical equation 1 mole of one gas will produce 1 mole of the other gas, so how does the gas even turn into the solid? So wouldn't the partial pressures of both increase?

Another way to think about it is to imagine a container with only B and C. That means a reaction cannot even occur, so when volume decreases, the partial pressures increase.

This is my thought on the problem. Can someone please explain to me what really happens?


texts: What is the refractive index of poly(methacrylamide)?

texts:
I've been looking for the index of refraction for poly(methacrylamide). I searched several vendors and in https://polymerdatabase.com/ with no success. Is there any database where I can find this information?

The refraction index of the monomer would be useful too.


texts: How do you figure out fuel specific impulse non-experimentally?

texts:
Simple question, probably very complicated answer:

Without building a test engine/rocket and finding out experimentally, that is to say, based on chemical characteristics alone, how can one compute the expected specific impulse of a given fuel?


texts: Reaction of solid silver sulfide on warming with dilute nitric acid

texts:
Solid silver sulfide is warmed with dilute nitric acid.

I thought that the nitric acid would engage with silver sulfide in a double displacement reaction, as follows: $\ce{Ag_2S {(s)} + 2H+ {(aq)} -> H_2S {(g)} + 2Ag^{+} {(aq)}}$. This double displacement reaction would be driven by the production of $\ce{H_2S}$ gas.

However, my textbook says that the answer is: $\ce{Ag {(s)} + NO_3^{-} {(aq)} + 4H^{+} {(aq)} -> 3Ag^{+} {(aq)} + NO {(g)} + 2H2O {(l)}}$. Does this redox reaction occur because $\ce{HNO_3 {(aq)}}$ is a strong oxidizing agent? Why doesn't the textbook answer contain $\ce{AgS {(s)}}$ in the left hand side of the net ionic equation?

In the future, how do I know when nitric acid will engage in a double displacement reaction to liberate gas, or when it will engage in a redox reaction? Furthermore, if the nitric acid was concentrated, then would $\ce{NO_2}$ be produced?


texts: Optional determination techniques in Atomic Absorption Spectroscopy

texts:
I have tried to find information about this case but I couldn't find anything specific.

The key point of instrumental methods of analysis, is for the student to be able to know which one of the possible methods to use for a specific determination. As for me, that is not an easy thing to do because every method has its pros and cons. For the moment I am analysing AAS (Atomic Absorption Spectroscopy), and I simply cannot tell:

What's the reason that $\ce{As}$, $\ce{Te}$, $\ce{Se}$, $\ce{Ge}$, $\ce{Sn}$, $\ce{Pb}$ is preferred to be determined only by the hydrid method? $\ce{Pb}$ for example can be determined also with the other methods in AAS

Does anyone have any tip, how to choose between methods if it's required for any element?

I replied with a similar question earlier about the mercury determination.


texts: Should there be a difference in the absolute energy gaps between bonding and antibonding MOs from the energy level of the AOs in the H2 molecule?

texts:
I have been reading Molecular Orbitals and Organic Chemical Reactions (Student Edition) by Ian Fleming. On Pg 5, Fleming mentions that the diatomic helium molecule cannot exists because there is an overall energy increase from populating both the bonding and antibonding molecular orbitals equally (i.e. putting 2 electrons into each). However, why should there be a larger absolute energy difference between the antibonding MO and the atomic orbitals compared to the energy difference between the bonding MO and atomic oritals? Fleming explains this by saying that this is due to the presence of inter-electronic repulsion in the MOs as there are two electrons present in each MO. This may seem to make sense.

However, in most MO diagrams, the energy levels of the bonding and antibonding MOs are drawn equidistant away from the energy level of the atomic orbitals. Does there seem to be a contradiction?

It is not a duplicate as I am proposing a new explanation of "inter-electronic repulsion upon population of the MOs", which has never been discussed before.


texts: Why do properties of colloidal solution depend only on dispersion medium's physical state?

texts: According to a past year JEE question, properties of colloidal solution depends only on dispersion medium's physical state and not on nature of dispersed phase or dispersion medium, or temperature of system. I cannot find any further information on this subject. I would like some clearer guidance on this. Would someone please help?


texts: How is the the law of chemical equivalence defined and what are its limitations?

texts:
I've heard that the law of chemical equivalence states that the gram equivalence of each of the reactants equals the gram equivalence of each of the products. But I'm facing difficulties in understanding double titrations. Moreover, this doesn't work for equations where the n-factor of all the reactants and products don't match.

Let's take an example:

$$\ce{KIO3 + KI + H2SO4 \to I2 + K2SO4 + H2O}$$

Here, the gram equivalence of $\ce{H2O}$ is $2$ which should match with that of $\ce{KIO3}$. But the gram equivalence of $\ce{KIO3}$ is $5$.

Similarly, $\text{g.eq}_{\ce{H2SO4}} \neq \text{g.eq}_{\ce{I2}}$ and so on. When the n-factors don't match, the gram equivalents don't match. Here, we can consider gram equivalent to be $\text{number of moles} \times \text{n-factor}$. Again, this n-factor is what is posing a problem.

  Can someone define the Law of Equivalence and state its limitations because of which I seem to find problems as I've mentioned above?


texts: Why don't equivalent hydrogens cause splitting in NMR?

texts: When doing NMR spectroscopy, it is an observed fact that equivalent hydrogens do not split one another. Why don't equivalent hydrogens split each other's signals? For example, why is the NMR spectrum for ethane a singlet instead of a quartet or even a dodecuplet (due to the hydrogens on the same carbon)? What is so special about hydrogens being equivalent to one another that causes no splitting to be observed?


texts: Increasing partition coefficient in an extraction

texts:
My friend had this homework question about supposing you had a slightly polar organic compound in an ether/water extraction with a partition coefficient in favor of ether. The question was:

  What simple method can be used to increase the partition coefficient?

My thought was to add salt to the extraction mixture. I was thinking that if you saturate the water with salt, there essentially isn't any room for the polar organic compound to stay in the water so it gets extracted into the organic layer. However, I'm wondering if there's a better explanation for why adding salt would increase the partition coefficient. Thank you for the help!


texts:
I wonder how photosynthesis works. I read the Wikipedia page, but I'm still confused.

My main gap of understanding is (I assume):

I know a photon changes the velocity of an electron. But I do not (fully) understand how a photon creates chemical reactions. Does the atom lose its electron due to this velocity increase and thereby attracting the electrons from the other atoms?

Is that all? Does this imply there is always an electron lost in photosynthesis or is that electron absorbed elsewhere (in another atom)?


texts: Why ZnS can be seen as the solution is made alkaline? Explain with reactions

texts:
There is an extract in my book which i am not able to get. It says:
Place strip of metallic zinc in aqueous solution of copper nitrate for about one hour. You may notice that the strip becomes coated with reddish metallic copper and the blue colour of the solution disappears. Formation of Zn2+ ions among the products can easily be judged when the blue colour of the solution due to Cu2+ has disappeared. If H2S gas is passed through the colorless solution containing Zn2+ ions, appearance of white zinc sulphide, ZnS can be seen on making solution alkaline with ammonia.


texts: Could PNP (Silicon) transistor be toxic when exposed to air\light?

texts:
The story goes as follow:

While I was in the electronic room I got bored and crushed a PNP transistor (Model CDIL 2N2907) using a rotating pipe jaws just like in the picture bellow.

Now, it took me some time to realize that I hear something like a sizzle or a tiny fire sound.
I looked at the crushed transistor and I saw a hole in the bent metal.

I am almost clueless in Chemistry, but I guessed that there was some kind of reaction
with the substance when exposed to air (Normal air in Temperature room about 20C)

I looked at the datasheet of the exact part: CDIL 2N2907
and I couldn't find any Chemistry info apart for the presence of silicon.

I do know that a N-doped semiconductor \ P-doped semiconductor are being used and in this case the semiconductor is silicon.

My question: Does (doped) silicon become toxic when exposed to air? Maybe there are other well known substances (insulator) being used with silicon when creating PNP that could react to air?

Also, the room had light (Fluorescent white light). Could it had any effects?

Thank in advance for any information on the matter.

Edit : The sound of sizziling came after I already crushed the transistor. Of course there was sound while crushing - of metal and more.

Rotrating pipe jaws:


texts: Oxygen production from thermal decomposition of metal oxides

texts: Does thermal decomposition of metal oxides always produce oxygen?


texts: How to distinguish between CsCl and NH4Cl by a chemical test?

texts:
$\ce{CsCl}$ and $\ce{NH4Cl}$ have similar reactions. For example, they can react with $\ce{AgNO3}$ to produce $\ce{AgCl}$ precipitate.
So my question is:

  Can we use a chemical test to distinguish between solid $\ce{CsCl}$ and $\ce{NH4Cl}$?

The $\ce{Cs+}$ ion is very unreactive and I do not know any reactions involving it. I believe the chemical test can somehow convert the $\ce{NH4+}$ ion into $\ce{NH3}$ gas so that we can test it with a moist red litmus paper.


texts:
I was just recently looking into some of the details of the different crystal structures that ice can freeze in. I was aware that many of the unusual properties of ice $I_h$ (the structure of “everyday ice”) are a result of the proton disorder necessary for the hydrogen-bonding arrangement it adopts.

What I also found is there are other arrangements of ice which are proton ordered and have nearly identical density to ice $I_h$. Now, I know density has no predictive value on what crystal structure will be taken (rather crystal structure can be used to predict density), but it seems unusual to me that there is such massive divide between ice $I_h$ and the rest of the ice srystal structures.

Is the entropic gain of proton disorder an explanation why ice freezes the way it does? Also, is there a large energy minimization associated with the hexagonal lattice that ice $I_h$ takes on? Doesn't it seem like a proton-ordered arrangement would be preferable over a proton-disordered arrangement? Or is it all much more complicated than that? It just seems like there should be a crystal structure of ice which is comparable to ice $I_h$ in energy, stability, etc. and yet there isn't.

I suppose a true answer to this question, because I admit it's rather broad, would deal with why the hexagonal lattice is so much more preferable for water than some other lattice arrangement. By dealing strictly with water, rather than crystals in general, I believe an answer to this question is more within reach.


texts:
I've been trying to find the mechanism for the gas phase decomposition of hydrogen iodide:

$$\ce{ 2 HI (g) <=> H2 (g) + I2 (g)} $$

Anyone know of sources where I can get information on this? I found a 1927 paper in PNAS but wondered if there is anything more recent. This is the 1927 paper:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1085202/

Proc Natl Acad Sci U S A. 1927 Oct; 13(10): 720–726.
The Photochemical Decomposition of Hydrogen-Iodide; the Mode of Optical Dissociation


texts: Why do tetrahedral complexes have approximately 4/9 the field split of octahedral complexes?

texts:
I am trying to calculate the relationship between the octahedral field splitting parameter ($\Delta_\mathrm{o}$) and the square planar field splitting parameter ($\Delta_\mathrm{sp}$) and thought a good way to start would be to understand why $\Delta_\mathrm{t}=4/9\Delta_\mathrm{o}$ for tetrahedral fields but couldn't find any information on it.

How does one arrive at this particular ratio mathematically?


texts:
We were discussing types of catalysts, homogeneous and heterogeneous.

Our question is: If you have two reactants, one reagent is aqueous and the other is a gas, and the catalyst is aqueous, what type of catalyst is it?

My guessing is that it is a homogeneous catalyst because the gas will dissolve in the solution at some point so that the reaction can occur. What is your guess?


texts: What does it mean that an electron quantum numbers are n1= 4 - l1?

texts:
I'm trying to solve some exercises from the 2017 IChO, and the problem 6-A1 states that

  in first ionization, an electron with the quantum numbers $n_1 = 4 - l_1$ is removed.

Now, I've never seen this way of expressing quantum numbers, and I don't know what it's supposed to mean, so I would appreciate it if someone could dumb it down to me.


texts: Why is no bromine liberated in the reaction of potassium bromide and concentrated phosphoric acid?

texts:
$\ce{KBr}$ reacts with concentrated $\ce{H3PO4}$ to give $\ce{HBr}$ and ($\ce{KH2PO4}$ or $\ce{K3PO4}$) (not sure which one, if someone knows it, please tell).

Why isn't bromine gas liberated?


texts: What happens when we pass sulfur vapors through cold water? What is the reaction for it? Which type is colloid is this? And why doesn't it form in hot or lukewarm water


texts:
I am trying to use UV-VIS for a 3D printed ~4mm PLA design. However I keep running into a problem because the polymer is not showing detectable under the UV-VIS. Does anyone have any suggestions that would allow for visibility of PLA? Any recommended papers would be of great use as well.

I also thought of possibly placing spider silk inside but this would implement an array of complexity in the product.

Thanks guys


texts: Choice of lower bound of curve for PV work

texts:
I am told that the area under the PV curve gives the magnitude of work done by a gas.
Let $V_i$ be the initial volume, $V_f$ be the final volume, and the pressure as a function of volume be given by $P=f(V)$. To my understanding, the work done is given by the area bounded by $x=V_i$, $x=V_f$, $P=F(v)$ and $y=0$.

Proceeding in the above stated manner, the work done comes out to be the sum of the areas of green and yellow region, but the answer stated neglects the yellow region.
Origin of Question : JEE MAIN
Here's the answer according to the official answer key released by the testing agency:


texts: Why is the HOMO-LUMO gap in N2 and CO of different sizes?

texts: Why is the HOMO-LUMO gap in $\ce{N2}$ and $\ce{CO}$ different even though they have the same number of valence electrons?


texts: On what basis are certain elements selected for doping silicon?

texts: I read online that transistors are made by doping silicon with other elements such as arsenic, phosphorus, or aluminium in order to increase its conductivity. How are these doping materials selected?


texts: Can a universal indicator turn colorless?

texts: I learned that litmus paper could be bleached by chlorine to turn colorless. I’m wondering if any chemical substances can react with all the components of a universal indicator such that it turns colorless, or stops being a pH indicator?


texts: Does a non-chiral substrate (2-bromo-2-methylpropane) also form two products via an SN1 mechanism?

texts:
If I have an alkyl halide, in which its tertiary carbon is non-chiral (for example 2-bromobutane), which reacts via an SN1 mechanism does it also produce 2 products?

I am asking because I know that the carbocation intermediate's plane of symmetry allows the nucleophile to attack equally well from either side and thus the product is a racemic mixture of enantiomers.  Is this also the case for a non-chiral substrate?


texts: How are there only 8 structural isomers of C5H11Br?

texts: Everywhere I see mentioned, that there are only 8 structural isomers of $\ce{C5H11Br}$. That is, the simple $\ce{C5}$ straight chain, $\ce{C4}$ with substituted methyl and $\ce{C3}$ with two substituted methyl groups, giving us a total of 8 isomers. But what about substituted ethyl groups? Or substituted bromo ethyl group like $\ce{C2H4Br}$? Am I missing something? Also is there a general formula to know the number of such structural isomers of haloalkanes?


texts: Rendering and visualization of orbitals of an atom?

texts:
I am looking for program that would display and render the orbitals of an atom.

Preferably display all orbitals. Specifically Argon.

Its not duplicate. I am looking for visual appealing rendered orbitals (hydrogen like) rather than exactness of the levels. And I would like to know which program will do it ?


texts:
Rephrasing:
The following reactions are a small example of my big system
$$(1)\  \ce{A + B <=> AB}$$
$$(2)\  \ce{AB -> CB}$$
$$(3)\ \ce{A -> C}$$
$$(4)\ \ce{C + B <=> CB}$$
with
$$\ce{\frac{[AB]}{[A][B]}} = 100 = K_e$$
$$\ce{\frac{[CB]}{[C][B]}} = 100 = K_e$$
I know the rate constants for reactions (2) and (3), and I know that
$$\ce{[A] + [AB] + [C] + [CB] = T}$$
with T =  some constant.
Now, although there is a fast equilibrium between $\ce{A + B}$ and $\ce{AB}$, and between $\ce{C + B}$ and $\ce{CB}$, I want to know how the concentration of each form changes with time.
But I dont know how to write down the differential equations of the system and include the equilibrium constant. Could someone please help me out? My only problem is how to include $K_e$ in the system of ordinary differential equations.


texts: How to calculate the theoretical yield of a Diels-Alder reaction?

texts:
A Diels-Alder reaction happens between 9-Anthracenemethanol (208.26 g/mol) and N-Methylmaleimide (111.10 g/mol).

I'm using 0.069 g 9-Anthracenemethanol (0.033 mol) and 0.11g N-Methylemaleimide (0.0009 mol, limiting reagent).

Since DA reactions have 100% atom economy, the product has the molar mass of both products combined, 319.36 g/mol.

Multiplying that by the moles of limiting reagent, we get 0.28 g product.
However, the mass of both starting materials combined (0.069g + 0.110g) together is not even 0.28g. What am I doing wrong?


texts: Yield of possible products from acid catalysed hydration of an alkene with a phenyl group

texts:
Here, (d) may be the major product due to high temperature.
My questions are:

Will a kinetically favoured (minor) product (c) form?

What shall be the order of yield of products?


texts:
I'm having trouble assigning priorities for this molecule:

I tried assigning priorities with the rules for doubly bonded atoms in mind. I know that the lowest priority group should be going into the page (not on a wedge) but I read that I can simply assign a priority with the fourth priority group on a wedge and then take the opposite of whatever I assigned as the true configuration of the molecule. Problem is, I get R. Answer key says S.


texts:
I am interested in the reaction of cyclobutylmethanol with HX where these are the only reagents.

My question is whether the reaction proceeds via SN1 or SN2. My reference text insists that primary alcohols are eliminated by SN2 even if the protonated alcohol is a strong leaving group. So if the reaction were SN1, there would be ring expansion.

What if I conducted this reaction in the presence of a Lewis acid like ZnCl2?


texts: Properties of starch in packaged pudding

texts: I had a mug of packaged pudding. The top layer of the pudding was of typical pudding consistency, while the bottom was more runny. What could have caused this?


texts:
According to the Wikipedia on real gases, it is stated that the expansion work done by a real gas differs from the ideal gas by $\int\left(V-\frac{RT}p\right)\,\mathrm dp$.

Firstly, does this mean $W_\text{real} = W_\text{ideal} + \Delta W$ or $W_\text{real} = W_\text{ideal} - \Delta W$?

Secondly, how is this formula derived?


texts: Stereochemistry of 1,4 disubstituted cyclohexane


texts: Confused by notation of atomic number Z and mass number A on periodic table of elements

texts:
I'm totally confused by the different conventions and when to use what. In the Periodic Table I see

$$\ce{^{6}_{12}C}$$

However, in books when talking about isotopes I see

$$\ce{^{12}_{6}C}$$

I don't understand the difference between the two. I know what the numbers mean but I don't understand when to use which convention. Are there names for these two conventions?


texts:
I just read about van der Waals radius and had some questions about it.

Would it be correct to say that in general, van der Waals radius decreases as we move from left to right in the periodic table?
The van der Waals radius of the noble gas in a period is larger than the radius of halogen that precedes it. Why is it so?
What is the difference between van der Waals radius for monoatomic (say neon) and non-monoatomic (say fluorine) gases?


texts:
What is the difference between $\ce{O}$ and $\ce{O2}$.

If C is carbon and then why $\ce{O2}$ is oxygen.


texts:
THE GIVEN QUESTION

MY ATTEMPT

The answer to this question was not given in my book.I want to know if this is the correct reaction mechanism and these are the products which are formed.


texts: What advantage is there in reporting the Lennard-Jones well depth in wavenumber units?

texts:
The Lennard-Jones well depth $\epsilon$ is typically given in energy units ($\mathrm{kJ}$ or $\mathrm{kcal}$; sometimes per mole). Jasper and Miller, however, reported $\epsilon$ values in reciprocal centimeters ($\mathrm{cm^{-1}}$).
Why use $\mathrm{cm^{-1}}$?

It seems unnatural using $hc$ as a conversion factor for a classical
description.
Absorption peaks (e.g. in wavenumbers) are not related
to the LJ potential well, which is for non-bonded interactions.

Ahren W. Jasper, James A. Miller, Combust. and Flame 2014, 161 (1), 101–110. (preprint pdf)


texts: Can an improvised torch be made to last for a prolonged period of time?

texts:
In the movie First Blood, there is a scene where Rambo is trapped in a cave after escaping a bazooka rocket that caused the mine he was hiding in to collapse. After realizing the entrance has been blocked, he decides to head down into the cave, and using the fire he built, a branch and some cloth he has, he prepares a torch (I can't remember now if he dips the cloth in some flammable liquid or not). Then he wanders through the cave for some time until he finds his way out, and the torch is holding up rather nicely... (he is seen feeding it with more strips of cloth from time to time)

My question is: is it realistic? Can a torch made from a branch and a burning cloth (whether or not dipped in gasoline or something else) be used for a prolonged period of time while remaining useful (i.e. not being burned-down, too hot to handle, etc.)?


texts:
Many sources including previous answers on Stack Exchange claim that it is antiaromatic.

But in a different yet similar question, I have also seen people saying that a monocyclic ring with 7 or more members can go out of plane to avoid antiaromaticity and become non-aromatic.

Shouldn't the same rule apply here as well?

Links mentioned:
https://chemistry.stackexchange.com/a/102606/74312


texts: Why does zinc plate copper in silver penny lab

texts:
In class, we performed a lab that involved heating a solution of zinc sulfate with zinc strips at the bottom of the beaker. A penny was placed on top of the zinc strips and soon after the penny became covered in a layer of zinc. What process causes the zinc layer to develop?

The explanation was that the zinc metal transferred electrons to copper which in turn reduced the zinc ions in solution, but this does not seem to make any sense as the zinc is being oxidized to just be reduced again. Why does this happen.  Is a thin zinc layer more stable?

Here are the instructions for the experiment


texts: Why does humidifier put measurable PM2.5 in the air?

texts:
(I know little science so please help me if I'm in the wrong place or if my question needs editing. I could use help with tagging, for example.)

I use two devices that measure PM2.5:

Kaiterra LaserEgg 2+, an air monitor which uses laser-based light scattering technology
Blueair Classic 280i, an air purifier which measures PM2.5 but doesn't say how

Generally, their PM2.5 measurements are within 20% of each other and the readings go up and down together.

Both devices are in a room measuring about 40sqm.

It's winter so the windows are closed and I keep the Blueair Classic on automatic mode, which varies the fan speed depending on the level of PM2.5 it measures. It is rare for the fan speed to increase above the lowest level.

The level of PM2.5 is usually under 10μg/m3 (safe, according to the WHO), as measured by the LaserEgg and the Blueair Classic.

A few days ago we felt that the air was dry (cracked skin, etc.) and our humidity sensors reports humidity around 25%, so we turned on an ultrasonic humidifier (https://www.amazon.co.uk/Humidifier-Improves-Health-Sleep-Focus/dp/B01C5YHFWO). We use tap water in the humidifier.

Within a few minutes the LaserEgg and the Blueair Classic reported a massive increase in PM2.5, to about 400μg/m3 (very unsafe according to the WHO). The Blueair Classic changed its fan speed to maximum but it seemed to have little effect. Perhaps the output of the humidifier is greater than the cleaning capacity of the purifier.

We have reproduced this situation several times since - every time the humidifier is turned on.

What could be causing the PM2.5 increase?

Could it be harmful?

P.S. This seems relevant: https://www.researchgate.net/publication/51859262_Indoor_particle_concentrations_associated_with_use_of_tap_water_in_portable_humidifiers


texts: What are the major environmental drawbacks with using methane as a combustable fuel?

texts: What are the biggest environmental issues with using methane, $\ce{CH4}$, (which is found as the major energy source in natural gas, shale gas, biogas, and synthetic natural gas), as a combustible fuel?


texts: Rationalising the reactivity of phosphoryl chloride

texts:
$\ce {POCl3}$ is a reagent well-known for enacting various functions in organic synthesis. For example, together with pyridine, it is able to dehydrate alcohols to give alkenes. Also, reacting it with a substituted amide gives chloromethyleneiminium ions. Salts containing these ions are also known as Vilsmeier reagents and they have great practical use in synthesis. The above two reactivity patterns seem to suggest that $\ce {POCl3}$ reacts with oxygen atoms containing rather high electron density, such that such reactions with other carboxylic acid derivatives at the carbonyl oxygen is not really observed. Firstly, I would like to ask if my rationalisation of its reactivity here is correct.

Also, as suggested by the same site, $\ce {POCl3}$ is also able to perform the halogenation of alcohol, in a manner similar to how $\ce {PCl5}$ performs the reaction, but only in the presence of dimethylacetamide (DMA) or dimethylformamide (DMF). Why is that the case? What particular properties of the solvent allow the transformation to be effected?


texts: In Lassaigne's test, the organic compound is first fused with Sodium Metal instead of any other Group 1 Metal, Why is this so?

texts: I know that Sodium has high polarising power than potassium so it can convert the respective functional groups more readily than Potassium and both Lithium and Sodium salts are soluble in water. This indicates that both Sodium and Lithium can be used but this is not the case as in each case the organic compound is first fused with Sodium to make respective ionic compounds and then identification tests are done. Why is this so? Why any other metal is not used?


texts: How does DIBAL-H react with acid anhydrides?

texts: I know DIBAL-H reduces carboxylic acids and some derivatives, but couldn’t find out about its reaction with acid anhydrides. Do these react? And what are the by-products (if any)?


texts:
During an isothermal reversible expansion of a gas, all heat absorbed by the gas from the reserviour is being used up to push the piston up. But doesn't this contradict something like the second law?
When I push a brick on a rough table, the motion will eventually stop and some heat will be generated due to friction, but If I get a bunsen burner and supply the same amount of heat, it brick won't move back to where it started.


texts: What is the difference between a bond, force, and interaction?

texts:
I am trying to explain why some solids are more soluble in water than others:

So the energy released from the formation of bonds between the solid solute molecules and water molecules compensate the energy needed to break the intermolecular bonds between water molecules and the intermolecular bonds between the solute molecules.

The problem is that I'm not sure if I have used the correct terminology, for example I have never used intermolecular 'bonds', I've only used intermolecular forces before.


texts: Is there any sort of AX3E2 molecule that consists of hydrogen atoms bonded to the main atom who is left over with two lone pairs of electrons? (Similar to ClF3 just with hydrogen instead of fluorine?)


texts:
I'm confused why the absolute configuration always has to change after an $S_N2$ reaction:

For example, in primary alkyl halide above there are 4 planes Nu can attack; and absolute configuration is changed after an $S_N2$ reaction because the nucleophile (Nu) only attacks the 'black plane'.
I can understand that the nucleophile wouldn't prefer red or green plane because of steric hindrance, but here's my question:

Why doesn't the nucleophile attack the 'blue plane'?


texts:
Does the term only refer to molecules that have the same symmetry elements or exactly the same symmetry operations. Online I see that its the same symmetry operation however my professor's slides show only symmetry elements.
Or is it depend on the writer; Dnh refers only to symmetry elements but D3h refers to symmetry operations but they are both point groups?


texts: How are natural orbitals derived from the electron density matrix?

texts: I have a $4\times4$ electron density matrix in 6-31G for $\ce{H2}$ using psi4 and I am wondering how to get the natural orbitals of the system. I have diagonalised the density matrix $\mathbf{M}$ into $\mathbf{M} = \mathbf{PDP}^{-1}$ where $\mathbf{D}$ is diagonal. Are the columns of $\mathbf{P}$ the natural orbital basis that can be used in integrals like the electron repulsion integrals?


texts: What causes KNO3 to decompose into KNO2 and Oxygen in gunpowder?

texts:
I've been studying fireworks and from what I understand:

$\ce{KNO3}$  decomposes to form $\ce{KNO2}$ and $\ce{O2}$ gas, and this free oxygen reacts with carbon to react with carbon and sulfur to form $\ce{CO2}$ and $\ce{SO2}$ gases in exothermic reactions.

What I don't understand is: What causes the $\ce{KNO3}$ to decompose, what is the purpose of using$\ce{KNO3}$  in gunpowder?


texts: Chemoselectively dihydroxylate a terminal alkene in the presence of an internal alkene?

texts:
The goal is to dihydroxylate the exo alkene, and then convert to a ketone.

Any suggestions would be apprecitated to either chemoselectively convert the terminal alkene, or directly convert the terminal alkene to a ketone.

Thank you!


texts: Bonding, multiplicity and quantum chemistry for FeP2

texts:
I’m trying to do some quantum chemical calculations for the linear molecule $\ce{FeP2}$ in the gas phase as well as its crystal (orthorhombic symmetry like here). I am lead to believe that in both cases iron has an oxidation state of +6, and phosphorous has an oxidation state of −3. My questions are:

Are such oxidation states a reasonable assumption for this molecule?
Would the molecule normally be a singlet (multiplicity of one)?
What quantum chemistry methods would be appropriate for this system?


texts: How is the absolute configuration of chiral molecular knots determined? What rules should be applied? For centrochiral compounds, the CIP rules are applied, for axially chiral is described here and for planar chiral here. I can't find the system for assigning R/S (or possibly some other stereodescriptors) for molecular knots, e.g  the attached knot doesn't contain an Sn improper axis, therefore it is chiral.


texts: Which is more stable out of the given carbocation?

texts:
Which is more stable?

$\ce{^+C(CH3)3}$
$\ce{^+C(CD3)3}$

I have read in Solomon's and Fryhle that the +I effect of D is more than that of H but here in this problem it is given that $\ce{(CH3)3C+}$ is more stable.
How is this possible? Since, deuterium enriches the electron density over the central carbon resulting in the diminishing of a positive charge eventually making the second structure more stable.
Second explanation can be on the basis of hyperconjugation which says that $\ce{-CH3}$ is better in showing hyperconjugation than $\ce{-CD3}$, but why is this so?


texts: Applied Potential and Electrochemical Cell Potential

texts:
Electrolysis of molten lithium hydroxide at $\pu{750 K}$ to form lithium metal
$$\ce{4 LiOH -> 4 Li + 2 H2O + O2}.$$
Electrolysis will only proceed at an appreciable rate when the applied potential exceeds the electrochemical cell potential by $\pu{0.60 V}.$
(c) Calculate the minimum potential that should be applied.
$$ΔG^\circ = -nFE^\circ_\mathrm{cell}$$
$$E^\circ_\mathrm{cell} = \frac{ΔG^\circ}{nF} = \pu{-2.60 V}$$

Why should the difference of $\pu{0.60 V}$ be added onto the absolute value of $E^\circ_\mathrm{cell}~(+2.60)$ and not $-2.60$?
I understand  $E_\mathrm{cell}$ is the measure of the potential difference between two half-cells in an electrochemical cell, but what is applied potential in this case?  I thought electrochemical cells produce an electric potential difference (in this case $\pu{-2.60 V}),$ so why would they need an applied (positive) potential difference?


texts: Is there a way to maximize van der Waals forces between two materials, by electrifying one material, thus creating dipoles/instantaneous dipoles and thus creating stronger van der Waals forces? has this been documented?


texts: How to convert from ppm to ug/m3 in case of PMx?

texts:
For $\text{PM}_{10}$, $\text{PM}_{2.5}$ sensors, sensitivity, minimum and maximum recordable concentrations are generally expressed in $\pu{ppm}$ (parts per million) while legislation uses $\pu{\mu g / m^3}$ or $\pu{mg / m^3}$.

For gases you usually use the molar mass to convert from one to the other.  Since PM is composed by heterogeneous particles how can I convert $\pu{ppm}$ to $\pu{\mu g / m^3}$? Is there an approximate weight for each type of PPM?


texts:
It is often explained that the relatively lower basicity of pyridine, relative to most amines, is due to the fact that the $\ce {N}$ lone pair resides in an $\ce {sp^2}$ hybridised orbital, instead of an $\ce {sp^3}$ hybridised orbital. the higher s character of the lone pair-bearing orbital thus holds on to the electron pair more tightly as the lone pair experiences more of the nuclear charge, decreasing the availability of the lone pair for donation to an acid.

Consider the data provided by Clayden, Warren & Greeves (2012), on p. 726. Yes, we observe the lower basicity of pyridine, relative to piperidine. This is consistent with the above rationalisation. However, based on the explanation above, the relative basicities of a typical imine and pyridine should be similar since in both molecules, the lone pair resides in an $\ce {sp^2}$ hybrid. Based on the data, it seems that the basicity of pyridine is around 3 orders of magnitude lower than that of a typical imine. Why is that the case?

Reference

Clayden, J., Greeves, N., & Warren, S. (2012). Organic Chemistry (2nd ed.). New York : Oxford University Press Inc.


texts: How to determine which of two metals will have the higher temperature after applying the same amount of thermal energy?

texts:
Two metal samples, $\mathrm{X}$ and $\mathrm{Z}$, of the same mass and initially at $\pu{25 ^\circ C}$, are heated so that each metal receives the same amount of thermal energy, which metal will have the highest final temperature?
  Specific heat capacities:
  $c(\mathrm{X}) = \pu{0.35 J//g*K}$,
  $c(\mathrm{Z}) = \pu{0.895 J//g*K}$

Does the specific heat capacity matter in the final temperature or not?


texts: Particle size vs dissolving rate of sucrose

texts: I’m required to make a lab with this information only (particle size vs dissolving rate of a solid (molecular covalent compound-sucrose)? so far what I’m thinking is using three different kinds of sugar like table sugar, sugar cubes, and one of them grinding it but the issues is how do you find how they dissolving rate?


texts: Can I get brief explanation of the reactions that occur under Glycolysis? What do the curved lines represent?


texts:
I am working on a personal project that involves a balloon filled with liquefied petroleum gas (LPG) at a pressure of $\pu{4 - 5 bar}$, and I need some kind of a device/filter that would convert it to gas (instead of liquid) at a low pressure. I used an industrial vaporizer, but it gave me something stronger than I need, and "not clean."

Basically, what i need is to build a very big lighter,
like this:

As you can see, just gas, and wick that turns to a "clean" fire, without all the side effects that the vaporizer creates.

Now, as I am missing a lot of knowledge here, I would like to know if someone could guide me through how I should do this, where I can find the things I will need, what the names and definitions for the stuff needed, etc.

EDIT:

When I used the phrase "home gas," which is common in my state, I meant liquefied petroleum gas (LPG).

Here is the vaporizer I use now (it belongs to someone who knows what he is doing, I do not plan on killing myself :) )

So, I will try to re-describe my problem:

I want to get a "clean, slow flame" such as a lighter has. What I am getting, regardless of the vaporizer pressure, is an unclean flame, as though some gas is not really burning and just comes out as well, or as if something in the process makes the flame burn dirtier.


texts: Its electronic configuration is $4d^15s^2$ so in normal state it has valence=1 and in energetic state, valence=2 (because our teacher said we count only the electrons in the outer shell firstly) and valence =3. First question: is it true what my teacher said? It was for Z=22 example, where she said it has the valence 2 and  4). Second question when we form the oxide we should use only the valence in the energetic states and not the one in the normal state?


texts: Stoichiometric defects in silver bromide

texts:
Stoichiometric defects (Schottky and Frenkel defects) in ionic crystals are formed due to irregularities in the ionic arrangement which maintain the stoichiometry and electroneutrality of the solid. It is known that $\ce{AgBr}$ shows both Frenkel and Schottky defects while most other compounds  show only one of these defects; for example, $\ce{AgCl}$ shows only Frenkel defects.

The ratio of the sizes of the cation and anion determines which type of defect is shown by the crystal. If the ratio is closer to unity, Schottky defects are more common, and if it deviates significantly from one, Frenkel defects are more common. Intuitively, this is correct since Frenkel defects involve the movement of the cation (or the smaller ion) into interstitial sites, which is indeed easier if the ion is very small as compared to the other ion, making it more mobile. Generally, the activation energy for cationic movement is lower. And if the ionic sizes are comparable, filling the interstitial sites is not feasible, and hence Schottky defects are more likely to be exhibited by the crystal.

The $\ce{Cl-}$ ion is smaller than $\ce{Br-}$ (i.e. the ratio $r_+/r_-$ for $\ce{AgCl}$ is closer to 1 than it is for $\ce{AgBr}$). Yet, $\ce{AgBr}$ displays Schottky defects while $\ce {AgCl}$ does not. Why is that so? (The size and hence the mobility of $\ce{Ag+}$ should be the same in both cases.)


texts: How to tell if a vibrational mode in benzene is IR and/or Raman active?

texts:
Consider the vibrational mode that corresponds to the boat-like bending of a benzene ring. Is it (i) Infrared active? (ii) Raman active?

This question was asked in an assignment in my college. However, all we've been taught is how to distinguish functional groups in organic molecules using characteristic IR frequencies, nothing else. From this I can tell that the C=O stretch in a carbonyl compound, for example, is IR-active. But how do we determine this for any molecule and any normal mode in general?


texts: When finding hybridisation of atoms, why are double bonds and triple bonds only considered once?

texts:
To figure out what hybridization an atom has is to just count the number of atoms bonded to it and the number of lone pairs. Double and triple bonds still count as being only bonded to one atom.   (Chem.Libretexts)

Why does this rule hold? Why are double and triple bonds counted only once?

Wouldn't a double bond have the equivalent number of electrons as 2 lone pairs?

And if orbitals are all about electrons, and there are three times as many electrons in a triple bond, shouldn't it count three times?


texts: How get a dilution at 150g/l of H2SO4 at 96%?

texts:
I've never done any chemistry before and I would like to get 5 liters of H2SO4 at a concentration of $150 [g/l]$.

One liter of $H_2SO_4$ at $96\% $W/W has a density of $1.84 [g/ml]$.

It means my bottle should weight $1840~[g]$ where I have $96/100\cdot1840=1766~[g]$ of pure acid.

5 liters of acid at $150~[g/l]$ means $5~[l]\cdot 150~[g/l] = 750~[g]$

The amount of acid at 96% is:

$$\frac{1840~[g]}{1766~[g]}\cdot 750~[g] = 781 [g] $$

Converted in liters I must have

$$\frac{781 [g]}{1840 [g/l]} = 424~[ml]$$

Eventually I need to poor 424 [ml] of $H_2SO_4$ at 96% into $ 5 [l] - 474 [ml] = 4.51~[l]$ of distilled water. Is that right?

I am wondering of the amount of heat will I get during this dilution. Is that ok to gently poor it (about 1 minute) into distilled water contained into a plastic jerrycan?


texts: Why does it require more energy to break the first O-H bond in water than is required to break the second O-H bond?


texts: Elimination reaction of 1-bromo-2-phenylcyclopentane

texts:
In the following reaction, treating the trans-1-bromo-2-phenylcyclopentane with ethanolic KOH gives an alkene. But in this case, the double bond is on the left side (less substituted) instead of being the more substituted one.

But why does this happen? Zaitsev's rule favours the highly substituted alkene. Even if a carbocation is formed, a hydride shift would have landed it on the carbon with the phenyl group, as the carbocation would be stabilised by resonance. Does the trans configuration forbid such reaction?


texts: Percent difference: What to place on the denominator?

texts:
I'm genuinely confused on what to put on the denominator for the formula $$\%~\mathrm{difference} = \mathrm{\left|theoretical~-~experimental\right|\over theoretical}$$ or some other similar formula with different variable names that mean the same thing.

Specifically, I have a reading on the iron content per pill written on the bottle, and I have an amount that I calculated from doing some math with the experimental data. The problem is, I know that the calculated value is experimental, but the iron content per pill isn't really theoretical because it's known. Anyway, which should I put in the denominator?


texts: What's the chemical reaction involved when adding Caesium to water?

texts:
According to the Notting Hill and Ealing High School, the reaction of caesium $\ce{Cs}$ with water $\ce{H2O}$ gives the following equation,
$$\ce{2Cs (s) + 2H2O (l) → 2CsOH (aq) + H2 (g)},$$
producing caesium hydroxide $\ce{CsOH}$ and hydrogen $\ce{H2}$, thus it's not hard to understand why is the reaction so violent.

But I don't really understand the reaction. Is this a single displacement reaction?

If so, why does the water break so fast into $\ce{H2}$ and $\ce{OH}$ ?

Is this related to caesium's weak electronegativity? ($0.79$ on the Pauling scale)


texts: Is N-methylimidazole an unusual solvent, or are there more common substitutes for it?

texts:
I want to test a process that was documented in the literature using N-methylimidazole.

I am not doing academic research, but rather testing a documented reaction for application to an industrial process, so I don't believe I need lab-grade chemicals.

When I look for this solvent online I can only find lab suppliers (e.g., Matrix Scientific, Acros Organics, Alfa Aeser) selling tiny quantities at very high prices.

Is there something unique to this chemical as a "donor solvent" that is not reproduced by any more common or inexpensive solvent?  I have seen it mentioned frequently in organic chemistry papers, but since I can't find industrial suppliers I assume it's peculiar to research.

The application I'm interested in is chemical stripping of lead using Rauchfuss's Elixir, which consists of sulfur as an oxidant and a donor solvent.  I haven't been able to learn why they used methylimidazole as the solvent in the study.  Obviously I would prefer one more widely and/or cheaply available.


texts: Why is 2s more stable than 2p, if 2p experiences greater effective nuclear charge?

texts: I'm referring specifically to this graph, which appeared in a chemistry lecture but which the lecturer could not explain. We know that 2s is lower energy than 2p. But surely those electrons in 2p orbitals, which apparently experience greater effective nuclear charge for Z > 10, would have lower energy! Can someone reconcile my understanding of orbital energy levels and this diagram?


texts:
According to the book Machine Learning Meets Quantum Physics

QM9 is built up from $\sim 134 \mathrm{k}$ drug-like molecules with up
to nine heavy atoms (C, N, O, or F).

I'm assuming that drug-like molecule is referring to Lipinski's rule of five. I used RDKit to plot 2D histogram of octanol-water partition coefficients (LogP) based on molecular weight (MolWt) and Polar Surface Area (PSA) based on molecular weight (MolWt)

These plots show that all molecules in the QM9 are below the suggested molecular weight interval of 180 to 480 and half the molecules have LogP below the -0.4 to 5.1 interval suggested by Ro5. I was wondering why they are called drug-like molecules? I'm using the following code to compute the properties:
from rdkit.Chem import Descriptors, Crippen

Descriptors.TPSA(mol)
Descriptors.MolWt(mol)
Crippen.MolLogP(mol)


texts: Why do I see two peaks for methyl salicylate in my GC–MS spectrum?

texts:
I ran a neat sample of methyl salicylate (CAS: 119-36-8) on the GC–MS and used $m/z~120$ as the quantifier and $m/z~92$ and $152$ as qualifiers. Below is the SIM spectrum for these ions, with two distinct peaks.

Both peaks are identified by the NIST spectrum database as that of methyl salicylate. Considering this is a neat sample and is not contaminated or diluted, why do I see two peaks in my spectrum?
GC parameters: $\pu{60 °C min^-1}$ ramp to $\pu{230 °C}.$


texts: Identifying Donation of an Electron Pair

texts:
Which one of the following reactions does not involve the donation of an electron pair?

A) $\ce{H+ + CH3NH2 -> CH3NH3+}$

B) $\ce{AlCl3 + Cl- -> AlCl4-}$

C) $\ce{CH3Cl + CN- -> CH3CN + Cl-}$

D) $\ce{Cl2 + 2I- -> 2Cl- + I2}$

The answer is D, but I don't know why.

The equation could be split into two half equations:

$\ce{Cl2 +2e- -> 2Cl-}$

$\ce{2I- -> I2 + 2e-}$

But surely this shows the iodide ion is donating a pair of electrons to the chlorine atom?

I'm sure really what approach I should take for this question.


texts: Will an alloy leaching in an acid act as both anode and cathode?

texts:
If an alloy is placed in an acid where selective leaching is occurring, will the alloy act as both anode and cathode?
If the alloy does act as both anode and cathode then will the potential difference be zero as the cathode and anode are shorted together?


texts: What software was used to create these organic reaction scheme figures?

texts: I am aware that software such as ChemDraw, ChemDoodle or MarvinSketch can be used to draw skeletal formulas and the like. But what can I use to draw (in a similarly professional way) reaction schemes, including the skeletal formulas, arrows, reagents/conditions above the arrows etc. such as


texts: Propagation of the uncertainty in measurements

texts:
The inside dimensions of a box that is cubic is 12.7 cm on each edge with an uncertainty of 0.3 cm.

What is the volume of the box?
What do you estimate to be the uncertainty in the calculated volume?

The first part is simple enough. To obtain volume of the box: $(\pu{12.7 cm})^3 = \pu{2.05E3 cm^3}$
Now for the second part, "estimate the uncertainty in the calculated volume?" – I would imagine that because the uncertainty is $\rm\pm0.3\ cm$ on each side the uncertainty in the volume of the box would be $\rm\pm(0.3)^3 = \pm0.027\ cm^3$? The textbook gives $\rm\pm0.60\times10^3\ cm^3$. I am (excuse the pun) uncertain of how they have reached this answer.


texts: Why is the melting point of BaCl2 > BeCl2 while CsCl<NaCl

texts: I'd think that increasing ionic character by increasing electronegativity difference would result in strong bonds but in the case of NaCl and CsCl(and the other chloride of the group) the case is different.


texts: Why did we introduce the concept of oxidation number in chemistry?

texts: Isn't oxidation number a weird concept? It assumes complete transfer of an electron from a more EN to a less EN atom per covalent bond formed. This assumption isn't even true. We know that partial $δ^+$ and $δ^-$ charges develop on the atom. Why did we introduce such a weird concept? And what is it good for?


texts:
Software: G09.Rev.D.01

=======gjf-file======

%chk=F:\Hanion.chk
# hf/sto-3g geom=connectivity

Title Card Required

-1 2
 He                 0.20408162    0.07288005   -0.00095405

 1

Causes error message #2070
Log file explanation:

 There are   2 occupied orbitals but only   1 basis functions!

But the same time for the Lithium which is the same electron structure, method STO-3G work fine.

Why Gaussian soft (STO-3G) causes error for Helium anion?


texts:
Prostaglandins are lipid substances derived from fatty acids, which act as powerful biochemical regulators.

In Wade's Organic Chemistry, they indicate that there are several families of prostaglandins (A, B, C, …) and that, according to this classification, a prostaglandin could be formulated as PGA1 or PGA2.

As an introduction it is very well explained, but I would like to go deeper into its nomenclature. I have searched on the Internet, but I have found nothing.

For example, the next prostaglandin is PGB1, but I don't know why. Nor would I know how to formulate one from its structure.


texts: Why does the carbonyl of carboxylic acids get protonated and not the hydroxyl group?

texts: Is the O of the C=O group more electronegative or is it for the sake of getting from product A to B that the carbonyl is protonated rather than the hydroxyl?


texts: Do Ligands electrons fill the d-orbitals of the metal ion?

texts:
We know that ligands make coordination bonds with d-orbitals of transition metals forming complexes. My question is, if that happened, all d-orbitals will be filled and no electron transition could happen between eg and t2g orbitals to be responsible for magnetism or colour formation.

I need clarification.


texts: In the blue bottle experiment, will it eventually be "used up" after repeated use?

texts:
The blue bottle experiment is a bottle half full of a colorless solution (dextrose, KOH, and methylene blue, in the version that I saw) and air that, when shaken, turns blue through the methylene blue oxidizing. Over time, the blue color fades while the methylene blue is reduced and the solution goes back to colorless. This can be repeated.

My question is, can this be repeated indefinitely, or is there some chemical in the solution that is being eaten up? Is the mechanical energy of shaking enough to sustain the reaction indefinitely? If it can be used up, what exactly is being used up?


texts: What is made at the copper cathode when electrolyzing water?

texts:
I just electrolyzed water with $\ce{NaHSO4 -> HSO4- <=> H+ + SO4^2-}$ with copper electrodes.
At the anode this reaction happened:

$\ce{Cu -> Cu^2+ + 2e-} \hspace{26 mm} E_0 = -0.34V$
$\ce{Cu^2+ + 6H2O -> [Cu(H2O)6]^2+}$

Can anyone confirm this last reaction? There was a blue-greenish substance falling to the bottom.
At the cathode this reaction happened:

$\ce{2H+ + 2e- -> H2} \hspace{27 mm} E_0 = 0V$

$\ce{2H2O + 2e- -> H2 + 2OH-} \hspace{5 mm} E_0 = -0.83V$
$\ce{OH- + H+ -> H2O}$

However, additionally, the cathode ($\ce{Cu}$) turned black. What reaction could have happened there? I electrolyzed at $12V$ using a car battery charger.


texts: How to compare the Heat of Combustion qualitatively?

texts:
I have been doing practice problems in General Organic Chemistry. I got some questions that asked me to compare the Heat of Combustion of some molecules. I couldn't get any of those questions and the logic behind their answers. I tried googling but it didn't help. The search results were not direct. So, I'd like to know the factors on which the heat of hydrogenation depends. I am not looking for an answer that describes it quantitatively but rather qualitatively.

Here are some example questions:

  Which one of the following has the smallest heat of combustion?

The answer is (c). But why is that?

  Rank the following substances in order of decreasing heat of combustion (maximum $\rightarrow$ minimum)

The answer is 2>4>1>3. But again, why is that?

I knew that the heat of combustion depends on the number of carbon atom. But in these two  examples the number of carbon atoms are same. Is there anything I need to watch out for?


texts: Search by CAS Registry name to obtain trackable accession: ie InChI?

texts: I'm updating a database and trying to move from CAS Registry names to InChIKeys. I have about ~800 compounds to track. Is there a way to do this mappings programatically? I'm looking for a web service or API that already has this implemented, does something like it exist?


texts: How to cancel once-mentioned element in thermochemical reactions

texts:
If I have three thermochemical reactions in a series(in order to find the enthalpy change) how can I cancel an element having not included in the reaction that's being asked about?

and only mentioned in one of the reactions ( either products or reactants)

e.g: $$\ce{NO + O3 \rightarrow NO2 + O2}$$
     $$\ce{O3 \rightarrow 3/2 O2}$$
     $$\ce{O2 \rightarrow 2O}$$

The reaction that is being asked: $$\ce{2NO2 \rightarrow 2NO + O2}$$


texts: Why can't equations of state be replaced by machine learning models?

texts: The Peng-Robinson equation of state, for example, has no underlying physical meaning, and is just a model that was fit to data. Computer scientists have developed much, much better models for data than messing around with polynomials and exponentials, like neural networks. Why can't standards organizations take a bunch of data about the chemical, fit a neural network or whatever to it, and publish that as the "EOS", instead of coming up with a meaningless equation that almost certainly wouldn't do as well?


texts: Salt crystal growing inside a mold inside a jar

texts:
I have recently found an experiment where you can grow a salt crystal on a jar. The experiment works like this: we take a jar, fill it with hot/warm water and start dissolving salt in it until it saturates (add food coloring - optional) and then leave it for a couple days after which on the bottom of the jar there will be a salt platform with crystals growing out of it. We take this formation out of the water and break it into pieces and take the nicest crystal, tie it with a string and then suspend it back in the water and over time (1-2 months) our crystal will grow in size.

My question is, if I create a solid plastic mold in which the water from the jar can infiltrate, if I put this mold in the saturated water and the crystal suspended right at the very top part of the mold and make sure the water is saturated from time to time, will the crystal grow perfectly or almost perfect all the way to the feet of the mold? I mean I want to start making salt figurines using a 3d printed mold and the salt experiment is it going to work?Thank you for you help I really appreciate your work.


texts: Calculate partial pressure of gases at equilibrium

texts:
I have the reaction $\ce{CO_{(g)} + Cl2_{(g)} <=> COCl2_{(g)}}$ where $K=4.5\times10^9$ at $100\ \mathrm{^\circ C}$

The first question was to find $K_p$ which I know is $K_p=K(RT)^{\Delta n}$ where $R=0.08206$, $T=273+100=373$ and $n=1-2=-1$. Put in the numbers and get $K_p\approx1.47\times10^8$.

Now comes the second question and this is where I get stuck:

  Equal moles of $\ce{CO}$ and $\ce{Cl2}$ are reacted at $100\ \mathrm{^\circ C}$. If the total pressure at equilibrium is 5.0 atm calculate the equilibrium partial pressures of the gases.

I have tried several solutions, where I either end up with a wrong answer or hit a dead end. I just don't understand how to solve this.


texts: How could I deduce what this organic compound would be?

texts:
For compound D (shown in the figure attached above), how can I deduce its structure?

I understand $\ce{CO2}$ has been produced and thus the compound will no longer have the $\ce{-COOH}$ group attached, but what I do not understand is why the double bond will get affected and why a nitrile will be produced?

I am unaware of what type of reaction/decomposition this is for the compound in square brackets (image above) , but I think compound D is supposed to be deduced backwards from its reaction with $\ce{LiAlH4}$. So what I can deduce is that something with $\ce{-CN}$ group in an organic compound can react with $\ce{LiAlH4}$ to produce another type of compound E which would be an amine. On the basis of knowledge I would deduce that compound E would have to be a nitrile.

Also in the image shown below, why is the latter isomer incorrect with that double bond left as it is from the original compounds shown in brackets in the image above?


texts: Why is dialysis tubing impermeable to sucrose?

texts:
This question was posed a couple years ago but not answered adequately. You can view the older thread here. The cellulose membrane commonly used in high school and university labs is widely available from suppliers such as Wards, Carolina, Flinn, PASCO, etc. The specifications are either available online or were obtained by contacting the companies and in each case the molecular weight cut off (MWCO) was between 6,000 and 16,000 Da. Regardless of the specifications these products are used to conduct osmosis demonstrations by placing 0.2-1.0M sucrose on one side of the membrane and to create water potential. In addition to having conducted this exercise myself the results are validated in countless examples online. The mass/pressure results from osmosis and a benedicts test indicate sucrose is not moving across the membrane.

Considering Sucrose has a MW of ~342 Da the previous explanations seem insufficient;

1) The pore size of the membrane is variable. True, but according to specs at least 10% of the pores are larger than the specification and even with variation of 0-6,000 Da (worst case) it would still be like throwing a tennis ball through a garage door 10% of the time.

2) Interactions between solute molecules, shape, and solute-solvent causing a larger solvodynamic radius. Sucrose doesn't have any charges I'm aware of, it has a simple structure, and even covered in water molecules it would still be much smaller than the pores.

Any suggestions or alternative explanations?


texts:
What is be the best commercially available source of highly nucleophilic iodide in non-polar solvent? Solvents used are cyclohexane, benzene, chlorobenzene.

I can get ahold of bromide quaternary ammonium salts at best. So I'm looking for equal substituent of Bu4NI. Any ideas?


texts: Rotational-vibrational spectroscopy of a molecule

texts:
I want to ask if the rotational-vibrational spectra of a molecule is related to any one mode of frequency or if it is related to the whole molecule?

Additionally, the vibrational levels that we say are composed of lower rotational energy levels. Are these vibrational energy levels of certain vibrational normal modes or of the whole molecule?


texts:
Diamond suppliers often "bake" stones. This causes them to expel yellow-causing nitrogen and become white, but also makes them more brittle. A baked diamond can often be recognized by its unnatural pasty white color.

Is there any scientific or chemical way to detect that a diamond has been heat treated?


texts:
My textbook says that an electrochemical cell works because of difference in reduction potential of two metals which cause one to lose electrons and other one to accept them. If a salt bridge is not used then the solutions of the two metals become charged and the reaction proceeds till the difference in reduction potential is cancelled by the difference in potential due to charges. All this theory seems to work well on paper, but it is never really explained why this reaction occurs.
What I mean is suppose you have a copper and a silver half cell. They are connected. The copper part does not know whether it is connected by a silver half cell or sodium have cell and I see no apparent of this information being communicated between the cells, so how does it know whether to get dissolved in the solution or precipitate out of the solution?
The book says that due to the difference in reduction potential, a potential gradient is set up which causes the charge to flow. I agree with this completely yet I am not able to grasp why this physically happens. What force causes to electrons to move from one electrode to the other? Especially when there is no salt bridge, the electrons move from positive electrode to negative electrode, which is completely opposite to anything I know.
I think that there must be some difference in local phenomena in the solution which spontaneously causes electrons to flow without any information being shared between the two electrodes. eg: At first I thought maybe copper having lesser reduction potential than silver would dissolve and precipitate out faster (basically a fast(?) equilibrium) which is completely independent of the other electrode and this difference speed would somehow cause the electrons to flow. I rejected this idea after a while but I still think difference in some sort of local phenomena in a half cell which is completely independent of the other half cell would drive the reaction forward.
Any thoughts?


texts: Elimination reaction with 1,2-dibromo-4-methylcyclohexane

texts:
I was doing a question from a practice exercise on the topic of elimination reactions and alkene synthesis. It is shown below:

I predicted that the product would be 1,2-diiodo-4-methylcyclohexane because I thought the reaction conditions favoured substition with iodide via the $\ce {S_N2}$ mechanism. Firstly, iodide is a rather good nucleophile and secondly, the substrate is a secondary alkyl halide. Even if it was not $\ce {S_N2}$, I would expect perhaps $\ce {S_N1}$ since iodide is a rather weak base and the conditions do not seem to favour elimination. However, the answer provided is very interestingly, 4-methylcyclohexene. Would someone kindly enlighten me on where I went wrong?


texts: I recently asked about the synthesis of iron (III) acetate. I want a rather concentrated solution to use as a calligraphy ink (which will be dissolved in alcohol/water). Will it be okay to heat the solution of iron(III) acetate, hydrogen peroxide, acetic acid, and water to evaporate all of the other reagents? That is, will heat cause the decomposition of the iron acetate?


texts: Will nitrobenzene and benzene have the same rate towards sulphonation reaction, since the formation of sigma complex is not the RDS of this reaction?


texts: Why does the colour of the same compound (e.g. magnesium nitride) differ?

texts:
When I am searching the colour of $\ce{Mg3N2}$ I came across photos showing different colours: greenish-yellow on Wikimedia,
and some other just yellow on some Google Images results.

I am eager to know what causes some samples to be bit greenish.


texts: Which of the following compounds will form significant amounts of meta product during mono-nitration reaction?

texts:
Hi, I tried to answer this question based wholly on the concepts of inductive effects. But haven't gotten anywhere with it.
I would appreciate any help regarding these questions:

What condition makes a compound to give meta product(instead of ortho or para)?
I know there is some flaw with my approach, so what is the correct way to do it?
Can this condition be applied to other compounds as well, or is it just for aromatic compounds?


texts:
Is it possible to derive the nuclear spin I=3/2 for $\ce{^23Na}$ from a term scheme or from something else from spectroscopy?

I thought the nucleus spin is empirical (and cannot be calculated from J and F values) or does it?


texts: A comprehensive list of theoretical approximations that are used in computational chemistry

texts:
I am having trouble recognizing all the approximations that are used in computational chemistry. I would like to start an answer list (similar as to the list of resources for learning chemistry) that addresses this question.

I will try to answer this question myself. I am hoping that anyone who is knowledgeable in the topic will correct and/or contribute. I am planning to start from general (e.g. Born Oppenheimer, LCAO) to specific (e.g. pseudopotential, functional). I am also planning to include why this approximation is necessary.


texts:
$15~ \textrm{mL}$ of $4 ~\textrm{N}$ hydrochloric acid, $ 25~ \textrm{mL}$ of $2~ \textrm{M}$ $\textrm{H}_3\textrm{PO}_3$ and a certain volume of $2.5~\textrm{M}$ sulphuric acid are mixed together and made upto $2 ~\textrm{L}$.
$30~ \textrm{mL}$ of this acidic mixture exactly neutralises $42.9~\textrm{mL}$ of a sodium carbonate solution which contains $0.1~ \textrm{g}$ of sodium carbonate decahydrate in $10 ~\textrm{mL}$ of solution.
The volume of $\textrm{H}_2\textrm{SO}_4$ added is?

I calculated the number of gram equivalents of sodium carbonate and thus calculated the normality of the acidic solution required.
I am having trouble with the statement "is made up to", so I'm assuming that this means that the solution is diluted with water to make a volume of 2 litres.
This seems to be yielding a negative volume. Can you tell me what I'm doing wrong?


texts: I recently read somewhere that electrons do not exist. it's just the electron density. Is it true that there are no electrons (particles) but only in the form of electron density? And does this contradict the fact of dual nature of electron?


texts: Why is phenol less basic than aniline in acidic medium?

texts: In acidic medium aniline is m-directing because of protonation of $\ce{NH2}$ group. But why doesn't the same happen in case of phenol, why is phenol an extremely weaker base as compared to aniline?


texts:
I am wondering what efect brewing tea (let us assume for the sake of simplicity it is green tea, brewed at about 80 °C) in deionized water might have on the product.

Will the lack of ions in the water increase or decrease the solubility of alcaloids from the tea leaves. Will the effect be different for alkaloids in salt and alcaloids in amine form?
Will drinking moderate amounts of such tea (0.5–1 l per day) detrimentally affect one's electrolyte metabolism? I am guessing maybe it does not matter, since the tea fills the water with electrolytes anyway – but will these electrolytes be significally different from what you would get in tap/mineral water? and if so, will it matter?


texts: Formulas for the number of spectral lines

texts:
While reading through Narendra Avasthi's Problems in Physical Chemistry, I came across two formulas on p. 64 (Scanned page):

  When electrons de-excite from higher energy level ($n_2$) to lower energy level ($n_1$) in atomic sample, then number of spectral line observed in the spectrum is

  $$\frac{(n_2 - n_1)(n_2 - n_1 + 1)}{2}$$
  When electron de-excites from higher energy level ($n_2$) to lower energy level ($n_1$) in isolated atom, then number of spectral line observed in the spectrum is

  $$n_2-n_1$$

Can anyone explain how the process of emission differs in these two cases?


texts: What will a polyurethane resin not adhere to?

texts:
For making a mould out of the bicomponent polyurethane resin kit that I have - I am going to need to take out the mould from its form. The mould is what I am actually making from the bicomponent resin.
I have done this once and i know how hard it is to take out the hardened resin out of the form it was poured into.
Is there any material I can apply on the form's walls for a smooth release of the hardened resin ? Maybe some sort of tape or powder ?


texts: What does the charge distribution around a Stone-Wales defect look like?

texts:
I'm reading a book on carbon nanotubes (P.J.F. Harris, Carbon Nanotube Science, to be specific) at the moment and puzzling about Stone-Wales or 5775 defects. This is where two adjacent carbons undergo a 90-degree rotation about their mutual centroid and generate a defect consisting of two five membered rings and two seven membered rings, as I've illustrated below (This is only supposed to be qualitative, and is on a finite PAH fragment rather than a nanotube, but you should get the idea):

I note that tropylium ($\ce{[C7H7]^+}$) is aromatic as a cation, and the ever famous cyclopentadienide ($\ce{[C5H5]^-}$) is aromatic as an anion, so what I'm wondering is: do the 5 and 7-membered rings in a Stone-Wales defect pick up either formal or partial negative and positive charges to maintain aromaticity in a fashion consistent with the rest of the structure?

P.S.

Big props to F'x, who attempted electronic structure calculations on the PAHs depicted, regrettably without SCF convergence.


texts: How can I remove a PEG shampoo from a natural horn-comb without damaging it?

texts: I washed by accident a horn-comb with a shampoo that contains PEGs, now how can I remove these types of chemicals from the horn-comb without damaging its surface?


texts:
I have read from sources here, here and even in my textbook that Copper (specifically $\ce{CuCl2}$ ) burns with a bluish green flame. All the sources mention that this is due to electron excitation and de-excitation in the orbitals of Cu. However, Why is copper the only transition element to give a coloured flame?

Most other flame tests are given by alkali metals and alkaline earth metals, which is understandable and is a common trend across the group. Copper stands out as an exception. I would like to know if there are any other transition elements that can give flame tests and the colours of the corresponding flames. I would also appreciate if someone could explain the electron excitation, either via Valence bond theory or by a Molecular Orbital treatment of a copper compound.


texts: How to find the mass of a solute given a mass fraction?

texts: How many grams of $\ce{CuSO4 * 5 H2O}$ are needed to prepare a $20\%$ (w/w%) solution of $\ce{CuSO4}$?


texts: What causes reactions to react the way they do?

texts:
We were taught that there are primarily four kind of reactions, synthesis, combustion, single displacement, and double displacement. When the reactants are given to you, the reaction can be predicted.

For example:

If the reactants are AB + CD, it will be a double displacement (two pairs of compounds)

If the reactants are AB + C, it will be a single displacement (one pair and one compound/element)

If the reactants are A + B, it will be synthesis.

Why do the "format" of the reactants determine the type of reaction? Why can't, for example, AB + CD synthesize to create ABCD? Or AB + C synthesize to create ABC? Why is it assumed that if the reactants are in a specific "format" a specific reaction will occur?


texts:
Question 1
The formula for concentration of cane sugar as a function of time is given by
$$k = \left(\frac{2.303}{t}\right) \log\left[\frac{\alpha(0) - \alpha(\infty)}{\alpha(t) - \alpha(\infty)}\right]$$
where $\alpha(t)$ is the optical rotation of the solution at any time t. This was the formula given in my textbook, but I feel it is wrong.
The optical rotation in the formula is the rotation of the solution, which includes rotation due to external factors which is taken care of by the $\alpha(\infty)$ term but it also includes rotation due to glucose and fructose , whereas the formula would only be valid if $\alpha(t)$ denoted only the rotation of cane sugar + external factors.
The reasoning given in the book is that the rotation due to glucose and fructose included in the external factors, but that is just wrong. The fundamental assumption is that rotation due to external factors remains constant and hence gets cancelled out, but if you include glucose and fructose in external factors, then their concentration and hence rotation is changing with time. Also they do not form a racemic mixture, so their rotations do not get cancelled out.
Question 2
Another question given in my textbook was to find the optical rotation if the reaction was 50% complete. Given rotations of cane sugar = 34, glucose = 10 , fructose = -20
The solution was $$\left(\frac{17+5-10}{3/2}\right)$$
Notice the 3/2 which represent the total moles in the denominator. If this is correct then the formula becomes even more incorrect as optical rotation also depends on total number of moles.
What is the correct formula? I am also not able to understand the calculation for total optical rotation as given in second question. Why did they divide by 3/2 and how does the optical rotation depend on the number of moles?