texts: Why is it possible to use lipids to recover diamonds in mining?

texts:
Diamond mining

This link says that diamonds will stick to "anything oleaginous" and that other materials slide down the fat that is applied to an inclined plane used in the mining apparatus.  I infer that the surface of the diamond interacts via dispersion forces and that other minerals are more polar.  Is this the case?  If so, would diamonds stick to wax or plastic?


texts: Understanding smoke chemistry of tobacco and/or marijuana

texts:
In an effort to understand the effects of tobacco vs marijuana smoke on health, the chemistry of smoking plants, and remembering some of the chemistry I took in college, I came across
a 2007 study comparing mainstream and sidestream marijuana and tobacco cigarette smoke,  according to which:

  a number of chemicals were
  present in marijuana smoke at levels that were substantially higher
  than in tobacco smoke. For example, NO, NO x , hydrogen cyanide, and
  aromatic amines were present in marijuana smoke at levels 3-5 times
  higher than in mainstream tobacco smoke, while ammonia was present at
  levels 20 times higher than tobacco. Conversely, some compounds such
  as PAHs, formaldehyde, and acetaldehyde were found at moderately
  higher levels in tobacco.

I have mostly understood the study but I do need some things clarified.

Question 1: Could the combustion of any plant material whether it is an edible herb or in my particular example, tobacco or marijuana, potentially produce similar products or by-products (e.g HCN, ammonia), because of the same functional groups present in the different compounds of the tobacco or marijuana plant?

Question 2: Would all of the molecules in the figure below which are found in the tobacco plant, be independently reacting with oxygen and what is the reaction of nicotine producing HCN and/or an aromatic amine which if I remember correctly is a cyclic molecule?

Picture source


texts: Why 9BBN's rings don't migrate during hydroboration-oxidation?

texts:
My organic chemistry textbook (Clayden, Warren, Greeves) says this:

If we use the $\ce{HBR2}$ reagent $\ce{9-BBN}$, then only the
non-cyclic substituent formed in the hydroboration reaction will
migrate, selectively giving us the product we want.

Why can't the original substituents of $\ce{9-BBN}$ migrate? It seems to me that there is nothing stopping the rings of $\ce{9-BBN}$ from migrating to the oxygen in the $\ce{-OOH}$ attached to the Boron.


texts: What are contrast agents in MRI and how do they work?

texts:
By reading some Wikipedia pages about MRI and MRI Contrast agent, I understand that contrast agents are mediums that reduce the relaxation times of the body tissues thereby increasing the contrast of the image obtained by MRI. My questions:

Are contrast agents just used for targeting a special tissue, such as a tumor, or they can be used the increase the contrast of the image of the whole body?
I know they decrease the relaxation time of the hydrogen atoms in body, but how do they do that?

Thanks


texts: Reason for formation of bubbles at boiling point

texts:
As I understand it, boiling takes place when the saturated vapour pressure equals to the atmospheric pressure.

But, why does the vapour pressure need to be equal to the atmospheric pressure for water bubbles to form?

According to this video, the atmospheric pressure is cancelled by the vapour pressure at boiling, which allows for the bubbles to form (due to the zero total pressure).

But, I think the atmospheric pressure is the same. So, if we consider the atmospheric pressure to be 1atm at a time, the surface of the water feels 1atm pressure every time (I mean that atmospheric pressure is 1atm as same as the before, but the vapour pressure and the air pressure is acting as a partial pressure according to Dalton's partial pressure concept, it doesn't affect the total atmospheric pressure.)

So what is the real reason?


texts:
Compound 1 was hydrothermally synthesized under autogenous pressure[1]

I've seen this term used a few times, but with no real explanation of what it means forthcoming. I suspect it refers to the synthesis being performed at equilibrium pressure inside a sealed container (the aforementioned synthesis is performed in an autoclave at 160 C). Is my intuition correct?

[1] Sun, et al., CrystEngComm, (2012), 14, 3982-3988


texts:
Taking a look at the phase diagram of water

By Cmglee - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=14939155

I see ice phases as much as up to 'Ice XI', but only one 'liquid' and one 'vapor' phase. Why is this? Either there are many ice phases, or too few liquid phases relatively.

The latter seems to be the case as it seems to be consistent with other substances. No matter what number of solid phases you get, there is usually only one liquid and one vapor phase.

Why are there so few common$^1$ fluid phases? What is the physical explanation for this?

1: For the sake of not complicating the answer too much, please ignore more exotic phases such as mesophases etc. If, though, your answer benefits from relating to them without confusing the reader too much, by all means $\ldots$


texts:
I am working with ozone measurements from two different sites (one rural and one urban). I am looking at the distribution of hourly averaged concentrations in air. The first figure shows the ozone distribution from the rural site and the second one from the urban site.

The first one (rural) looks normally (or lognormally) distributed, whereas the second one (urban) looks exponentially distributed.

My hypothesis is that it is caused by the fact that there is more pollution in an urban area, therefore more ozone depleting substances and this is why we have mostly small values, creating an exponential distribution. I am wondering if there is a more precise explanation that these distributions of the same molecules are so different.


texts: Putting high symmetry points labels to a band structure plot

texts:
So far I've got this plot using Quantum Espresso. I want to put gamma, X, L, etc labels to the k-path.

Quantum Espresso's ouput states the following:

 high-symmetry point:  0.0000 0.0000 0.0000   x coordinate   0.0000
 high-symmetry point:  0.0000 0.5136 0.0000   x coordinate   0.5136
 high-symmetry point: -0.5136 0.5136 0.0000   x coordinate   1.0272
 high-symmetry point:  0.0000 0.0000 0.0000   x coordinate   1.7536
 high-symmetry point:  0.0000 0.0000 0.1556   x coordinate   1.9092
 high-symmetry point:  0.0000 0.5136 0.1556   x coordinate   2.4228
 high-symmetry point: -0.5136 0.5136 0.1556   x coordinate   2.9365
 high-symmetry point:  0.0000 0.0000 0.1556   x coordinate   3.6628

However I was expecting these points to be the high-symmetry points:

How should I label the k-path then?
I'd like something like this:

But I guess I'm not understanding QE's high-symmetry points output.


texts:
The reduction potential for $\ce{AgI}$ is $-0.15\ \mathrm{V}$ and for $\ce{AgCl}$ it’s $0.22\ \mathrm{V}$. As $nFE =-\Delta{G} = T\Delta{S} - \Delta{H}$ this must imply that $\ce{AgI}$ is a stronger bond in order for it to be negative.

I would think $\ce{AgI}$ is weaker due to having a much larger ionic radii for $\ce{I-}$ than $\ce{Cl-}$ and the lack of covalence due to a smaller $\Delta\chi$

I think that it must be something to do with the size of the $\ce{I-}$ mean that it causes significant ordering of the water molecules in the solution and it's this entropic effect that is actually the key idea as otherwize I can't rationalise it at all.


texts: Why is only one part of buffer in the reactants side?

texts:
Given that buffers consist of either

a weak acid and its basic salt, or
a weak base and its acidic salt

and that the buffer consisting of CH3COONa and CH3COOH is added to water (H2O) ...

The reaction is:
$$\ce{CH3COOH + H2O <--> CH3COO- + H3O+}$$
(Equivalent reaction is $\ce{CH3COO- + H3O+ <--> CH3COOH + H2O}$)

Why aren't both parts of the buffer that is being added to the water represented in the reactants side of the reaction?

In other words, how is it that one part of the buffer is making another part of the buffer if both needed to exist in order to be a buffer to add in the water in the first place?


texts: Will phosphorous Ylide participate in carbene generation and insertion?

texts:
The following question was sent to me . The answer for this question was given to me as  option b

I attempted it as following , recognizing the first step as a ylide reaction with a carbonyl compound.

In order to get option B , I have to assume ylide generating a carbene and this may insert to double bond.

I have not come across phosphorous ylide as carbene generating reagent.

My question is as follows:

Will phosphorous Ylide participate in carbene generation and insertion in the presence of double bond ?

An answer in this regard would be quite help full.


texts: Adiabatic compression of an ideal monatomic gas. What would the change in entropy be?

texts:
Two moles of an ideal monatomic gas initially at 300K and a pressure of 2 atm is compressed adiabatically using a constant external pressure $P_{ext}$ until equilibrium is reached. The temperature of the gas is then 400K

a) calculate w, q, $\Delta U$, and $\Delta H$ for this process

b) calculate the final equilibrium pressure $P_f$ of the gas (note $P_f =P_{ext}$)

c) calculate $\Delta S$for this process.

a) I calculated $\Delta U$ by $\Delta U= nC_v\Delta T$. Since it is an ideal gas, the $C_v= \frac{3 }{2} R$. From that I got $2494.2$ J for $\Delta U$. Then, since it's adiabatic, q = 0, thus w = $2494.2$ J. I calculated $\Delta H$ using $nC_p\Delta T$. As $C_p$ would be $\frac{5}{ 2} R$, $\Delta H$ is $4157$ J.

b) I used the ideal gas law $V_2= \frac{nRT_2}{P_2} $and subbed it into $w= -P_{ext}(V_2-V_1)$ and as the question says$ P_f  (P_2)= P_{ext}$ I managed to eliminate some variables to end up with a $P_{ext}$ of 3.68 atm.

c) I don't know how to do this. I'm confused as to what formula to use for this. We can't use the $\frac{q_{rev}}{T}$ one since it doesn't state in the question if this is a reversible process. There are 2 other ones I learned, but they can only be used when it's isothermal or constant volume/constant pressure. They are:


texts: Using electrolysis of water as a proton generator

texts:
I'm working on a project right now, where the challenge is to try to use electrolysis as a way of controlling the $\ce{pH}$ of water.

I've set up an experiment where I have two separate chambers or volumes of water.
Both chambers are connected to the same electrolytic unit. The flow of water is from a respective chamber, into the unit and then back into the same chamber again, in an attempt to separate the two half reactions. For this reason I call the chamber that flows over the anode for the anodic chamber, and the chamber that flows over the cathode for the cathodic chamber. The bodies of water are separated in the electrolysis cell by a proton-exchange-membrane (PEM) that should, in theory, only allow positively charged ions to cross.

Apologies for the Danish text on my setup, but the figures should help you understand what I'm trying to do.

The anodic chamber (the water that goes to the anode half-reaction of the electrolysis cell) contains tap water while the cathode chamber contains Milli-Q water with added $\ce{NaCl}$ for conductivity purposes.

The $\ce{pH}$ of the water is alkaline in both chambers when the experiment starts, but I've also tried to run the experiment where the anodic chamber is acidic.

Anyway, here is what I hoped would happen in alkaline water:

Anode (oxidation):

$$\ce{4OH- (aq) -> 4e- + O2(g) + 2 H2O(l)}$$

Cathode (reduction):

$$\ce{2H2O (l) +2e- -> H2(g) + 2OH-(aq)}$$

In theory, I was expecting the $\ce{pH}$ to drop in the anodic chamber, since removing $\ce{OH-}$ would necessitate a flow of positively charged ions across the PEM membrane, instead of the $\ce{OH-}$ produced in the cathodic chamber in order to satisfy electronegativity. This would also mean that the $\ce{pH}$ should rise in the cathodic chamber.

However, what I see is invariably that the $\ce{pH}$ rises very rapidly, and continuously, in the cathodic chamber, whereas the $\ce{pH}$ in the anodic chamber remains either stagnant or rises very slowly.

Now, part of the reason for the rapid rise in the cathodic chamber is the complete lack of alkalinity, that much is clear to me. However, I don't understand why only the reduction half cell reaction seems to occur.

The only explanation I have been able to come up with is that something else on the anode half-reaction is donating electrons to the reaction. I tried running the experiment at different voltages in the hopes of finding a "sweet spot" that would prevent this "something" from reacting but as of now I haven't been able to do that. I'm worried it may be that my anodic electrode is donating the electrons.
My electrodes are nickel based.

A cursory glance at Wikipedia shows the standard electrode potential of nickel as

$$\ce{Ni^2+ + 2 e− <=> Ni(s)} \;\;\; \pu{E^{\circ} = −0.25 V}$$

And for my hydroxides

$$\ce{O2(g) + 2H2O + 4 e− <=> 4 OH−(aq)} \;\;\; \pu{E^{\circ} = +0.401 V}$$

When I run the reaction, I also see a yellowish/greenish precipitate forming in the anodic chamber, which according to some lab technicians at my location may be the nickel reacting.

Anyway, the question(s) are then - what do you think is happening  in my system, given this information?

Am I on the right track? should I try to change my electrode?

Have I made some obvious, basic mistakes?

What suggestions do you have, so that I can get this to work?

I hope that you have the time to advice me on this, and I wish you all a pleasant day.


texts: Using Dalton's law of partial pressure to find percentages of composition

texts:
A mixture of helium and neon gases is collected over water at $28.0 \rm~^\circ C$ and $745\rm~ mmHg$. If the partial pressure of helium is $368\rm~ mmHg$, what is the partial pressure of neon? (Vapor pressure of water at $28\rm~^\circ C =28.3~mmHg$). Calculate the weight percentage of He and Ne in the original mixture.

The question is based on Dalton's law of partial pressure. I got the first part right.In the second part, since we have to deal only with the original mixture, total pressure should be $$745-28.7=\pu{716.7 mmHg}$$ So we calculate the total moles in terms of "v" (total volume) and then moles of neon and helium in terms of "v" from which we calculate the weight of neon and helium and calculate the weight percentage. "v" will eventually cancel out and we get weight percentage of neon as $34.54\%$ and that of helium as $65.45\%$ but that is not the right answer.
In the solution to this question, they took the total pressure while dealing with the second part as $\pu{748 mmHg}$ only but why would we do that. We are only talking about the original mixture. Where am I wrong?
Answer in my textbook : Neon weight% = $82.58 \%$, helium weight% : $17.43\%$


texts: Distillation of methanol and water - Temperature Change

texts: We tried the synthesis of methyl benzoate in the lab via the Fischer Esterification reaction with excess starting methanol. After 1 hour of refluxing the reactants we immediately set up a simple distillation procedure to remove the excess methanol and here lies my question. By closely monitoring the temperature of the thermometer the mixture started boiling at 70+ oC and continued to rise slowly as expected. At one point the temperature started dropping slowly and after asking the professor she said that the distillation was over. I fail to understand why the temperature dropped. Can someone provide insight as to why it dropped and furthermore what should the thermometer show from start to finish and why? To my knowledge, the solution before the distillation contains methanol, some benzoic acid, methyl benzoate, sulfuric acid and water. Thank you in advance.


texts:
There are 7 different gas cylinders filled with:

nitrogen
oxygen
air
methane
hydrogen sulfide
carbon dioxide
sulfur dioxide

How do I determine how much of the respective gases is left?

Nitrogen and oxygen are in a gaseous state, so I reckon a glance at a pressure indicator will do. Air? The same. How about the last four cylinders which are filled with liquids? They have their vapor pressure, but I am not sure that those pressures can be used to accurately calculate the volume of respective liquids. Should the weight of the cylinder be measured?


texts: What optical methods can be used to measure the concentration of reacting gases in a reactor during an exothermic and fast reaction? I need to monitor and measure the local concentration of my gases (in the methane production reaction) along a reactor bed in order to be able to clarify the kinetics of this reaction. Which optical techniques are able to make such measurement?


texts: How to verify the accuracy of a pH meter

texts:
One suggestion I received is that I prepare a solution of a known activity and probe the solution with the pH meter. The problem I see with this is that any error in solution preparation can lead us to conclude that the pH meter is faulty.

Is there any other way to test the accuracy of a pH meter? We need to make extremely accurate measurements (we are studying the activities of ionic solutes).

Also, what solution has an activity of exactly 1.0?


texts: Is storing diluted (~1M) sulfuric acid, HCl, NaOH, etc. in plastic PET bottles a bad idea?

texts:
Do I really need glass bottles if the acids and NaOH is so diluted? I thought plastics dont really react with acids. And I already have them in plastic bottles (probably a different kind).

Thanks


texts: How do I name a substituent which is a cycloalkane which is attached by a chain of more than one carbon?

texts: Above is a picture of an alkane. How would I name this using IUPAC rules? I understand how to name other substituents such as (1,1-dimethylethyl) and some other methyl groups, but I don't know how to name the cycloalkane substituents. What are the rules for naming cycloalkanes as substituents?


texts: How many valid resonance forms can be constructed for aniline?

texts:
Based on the above picture, it seems that there are four. However, I have two questions:

Aren't the top right and bottom left forms simply mirror images of each other, and thus considered the same?
If not, would an alternate version of the top left form be a fifth structure, if the double and single bonds were flipped?


texts: Restricted open-shell versus unrestricted methods for open shell systems

texts:
Open-Shell systems (radicals and so on) can be modeled by single-determinant quantum chemical methods using unrestricted (u) or restricted open-shell (ro) methods (I am aware that single-determinant approaches are not always reasonable for open-shell systems, but let's ignore that for a second and suppose we have to use a single-determinant method).

Unrestricted calculations may suffer from spin-contamination. Restricted open-shell calculations remedy this, they are unaffected by spin-contamination. However, restricted open-shell methods are much more computationally expansive. Also, Koopmans' theorem cannot be rigorously applied in the case of ro calculations.

My question is:

Apart from the before mentioned issues, are there any disadvantages of restricted-open-shell computations in comparison to unrestricted calculations? Are there any situations where an unrestricted calculation would be more appropriate than a restricted-open-shell calculation?

[Methods of interest are - for example - MP2, DFT and HF.]

There is already a somewhat related discussion: U- or RO-method for Singlet-Triplet Gap?. However, my question is much broader, it includes for instance: Are there cases when it is absolutely not ok to use ro methods, and you have to use unrestricted methods?


texts:
If two alkali metal atoms join with an oxygen atom, an ionic bond forms. Since hydrogen has the same number of valence electrons as alkali metals, why can't water be ionic?

This is what I'm thinking:

$$
\ce{(H^+)_2O^{2-}}
$$

Thank you


texts: I'm imagining a strong base like NaNH2 attacking the adjacent carbon of the ether, giving the oxygen a lone pair and forming an alkoxide. NH3 has a pKa of 36 while an alcohols (conjugate acid of alkoxides) have a pKa of around 15 so shouldn't this be favorable?


texts: Why are palladium and platinum carbonyls unstable at room temperature?

texts:
By palladium and platinum carbonyls, I mean the mononuclear, homoleptic, charge-neutral, binary carbonyl complexes of the form $\ce{M(CO)_n}$ and not any heteroleptic complexes like $\ce{Pd(CO)(PPh3)3}$ and similar compounds of platinum which are abundant in chemical industry and used as catalysts.

So, I was reviewing carbonyls of transition metals when I encountered this statement:

  Group 10 elements with 10 valence electrons form metal carbonyls
  $\ce{Ni(CO)4}$ ($10 + 4 \times 2 = 18$ electrons). Curiously $\mathbf{Pd(CO)_4}$ and $\mathbf{Pt(CO)_4}$ are not stable.

I am proposing that heavy metal carbonyls tend to be unstable(?) and decarbonylate to form polynuclear carbonyls. For example: $\ce{Ru(CO)5}$ and $\ce{Os(CO)5}$ being unstable form $\ce{Ru3(CO)12}$, and $\ce{Os3(CO)12}$. But in the case of palladium and platinum, no carbonyl complex seems to exist in stable condition at room temperature. I reviewed two papers which described the Group 10 carbonyl complexes (links below):

  Complexes where the carbonyl group is the only ligand present have
  been reported for all the platinum group metals except
  palladium.[...] No substantiated reports have been published on
  platinum or palladium compounds similar to the nickel carbonyl
  $\ce{Ni(CO)4}$. Thus the polymeric platinum dicarbonyl is the only
  known carbonyl of these two metals and even this compound is unstable
  in air.[...]

  The unstable polymeric platinum dicarbonyl $\ce{Pt_n(CO)_{2n}}$ has
  been obtained as a cherry red precipitate by the action of carbon
  monoxide on aqueous or ethanolic solutions of Pt(II) compounds (e.g.
  $\ce{K2PtCl4}$) at temperatures up to 80 °C; or as a purple colloidal
  precipitate by the action of water on a benzene solution of
  $\ce{Pt(CO)2Cl2}$ under an atmosphere of carbon monoxide.

  It was not until 1972 that a definite existence of the congeners
  $\ce{Pd(CO)4}$ and $\ce{Pt(CO)4}$ was reported. Using matrix isolation
  and Raman techniques, data for the products of Pd atoms CO and CO/Ar
  cocondensation reaction were able to characterize the series of binary
  complexes $\ce{Pd(CO)_n}$ analogous to $\ce{Ni(CO)4}$, the most stable
  being $\ce{Pd(CO)4}$ but still unstable than $\ce{Ni(CO)4}$ which
  explains the failed attempts in its synthesis. Similar technique were
  used in making $\ce{Pt(CO)4}$ at 4.2-10 K which is stable up to 30
  K.  (slightly abridged)

The question is: why they are unstable/don't exist at room temperature?

Platinum Metals Rev., 1972, 16, (2), 50 "The Carbonyls of the Platinum Group Metals" By C. W. Bradford, Research Laboratories, Johnson Matthey & Co Limited (link)
J. Am. Chem. Soc., 1973, 95 (22), pp 7234–7241 "Binary carbonyls of platinum, Pt(CO)n (where n = 1-4). Comparative study of the chemical and physical properties of M(CO)n (where M = nickel, palladium, or platinum; n = 1-4) DOI: 10.1021/ja00803a009


texts: What is the physical state of vitamin E acetate at room temperature and normal pressure

texts:
Vitamin E acetate ((+)-alpha-tocopherol acetate) is sold as semi-solid/liquid by Sigma and their safety data sheet gives the melting point as 25 °C. On the other hand, internet databases such as Chemspider show melting points of either -28 °C or 28 °C. Supplements labeled either Vitamin E or Vitamin E oil are packaged as solid, gel capsules or liquid.
What is the normal melting point, and what is the physical state at room temperature (20 °C)?
Update
There are at least three products on the market, the single (+) stereoisomer (derived from biological sources, CAS 58-95-7), the racemic mixture, and the "all-racemic mixture" (8 stereoisomers, with some pairs being diastereomers and other pairs enantiomers). The latter is produced synthetically with non-stereospecific steps (CAS 7695-91-2). All have the formula $\ce{C31H52O3}$. To clear up any confusion, the physical state of the single isomer, of the (+/-) racemic mixture and the "all-racemic mixture" would be of interest.
Vitamin E, depending on the source, has different numbers of methyl groups on the aromatic ring; these forms are referred to as alpha, beta and gamma. The alpha form is more common in Europe while the gamma form is more common in the US (due to different diets).


texts:
Why do ionic compounds have higher melting and boiling points despite having smaller radii?

I thought that the closer the two ions are, the larger the repulsive force, and therefore it should rather require less energy to separate them (and at further distances apart, a lower melting point is observed because there is less attraction).

This is not a question of ionic compounds vs. covalent compounds, which is covered in this question. To be clear, I am interested in the comparison of ionic compounds with ionic compounds.


texts: Is it possible to cut yourself on pyrite?

texts:
I am planning an RPG adventure where the characters might end up getting a large cubic lump of "gold", which in reality, as you might have guessed, is in fact pyrite.

I also wanted to plan for the contingency that the group wouldn't notice that it's not the real deal, so I thought I could maybe let one of the characters cut himself on the crystal. A quick google search yields images such as this:

(Source)

This looks pretty sharp and possibly blood-drawing, but is there a way to know for sure? Any recommendations as to how to handle sharp minerals? Any first-hand experiences?


texts:
I have recently reviewed the synthesis of the dehydrating agent DMC (7), but I could find no reported mechanisms for its formation. I have proposed the mechanism drawn below, but I am unsure about a few steps.

To start, It is clear that this reaction is similar to the Vilsmier-Haack reaction, as the product is identical to what would be obtained under Vilsmier-Haack conditions; however, it is obvious that a different mechanism must be followed (the lone pair of the imidazolidinone (1) will not be attacking anything after all). I proposed that traces of HCl in the reaction will result in the formation of intermediate 2. The enol form of this can then attack the phthaloyl chloride (3) as expected to form intermediate 4. Of course, this will collapse to form intermediate 5. With no better nucleophiles in the reaction, the expelled chloride will attack intermediate 5. Nitrogen's lone pair could then kick out a carboxylate as a leaving group (I am not very confident about this step). This would form the desired DMC (7).
Now, I would ask why it was necessary to use phthaloyl chloride as opposed to a simple monoacid chloride. I propose this is because the phthaloyl chloride quickly destroys the nucleophilic carboxylate, which might otherwise react with the DMC to form unwanted byproducts. The resulting phthalic anhydride is not nucleophilic, and in the absence of any traces of water, it will not react with the DMC.

Now, I have 2 questions.

Does my mechanism for the formation seem correct? Only traces of HCl will be present in the reaction, so I am not sure if the concentration of the enol form will be enough to react at a reasonable rate. Also, the loss of carboxylate as a leaving group is a little bit worrisome, as always.

Because this reaction is so similar to the Vilsmier-Haack reaction, would Vilsmier-Haack conditions be a viable way to form the DMC?


texts: What is the difference between hydrogen chloride and hydrochloric acid?

texts: My teacher insists that hydrogen chloride is a misnomer, and that the proper nomenclature demands HCl to be named hydrochloric acid. However, I saw the name hydrogen chloride used in my textbook, but it was never further explained.


texts: Is the bond in HF ionic while it is covalent in HCl?

texts: Why would a hydrogen atom "donate" to fluorine in an ionic bond but not in $\ce{HCl}$?  Why would $\ce{H}$ and chlorine share instead of $\ce{Cl}$ just stripping it away like $\ce{F}$ does?


texts: How is the Felkin-Anh model of stereoinduction correctly explained with MO theory?

texts:
One method to predict stereoinduction in asymmetric reactions is the Felkin-Anh model (derived from the more basic Cram model) that applies to nucleophile attacks on α-chiral aldehydes. In a simple case such as (S)-2,3,3-trimethylbutanal, assignment of large, medium and small residues is trivial and we predict nucleophile attack as indicated in scheme 1 to generate (2R,3S)-2-hydroxy-3,4,4-trimethylpentanenitrile.

Scheme 1: Felkin model for all-carbon systems.

In some cases — I was taught ‘in cases of a group with high electronegativity on the α-carbon’ — we may no longer consider simply the size of the substituents but instead need to consider the electron-withdrawing substituent to be orthogonal to the carbonyl bond axis. Examples would be α-haloaldehydes, α-silyloxyaldehydes or α-aminoaldehydes as shown in scheme 2 with (S)-2-substituded butanal.

Scheme 2: Felkin-Anh model for systems containing electronegative $\ce{X} = \ce{Br, Cl, OTBS, NHR, etc}$.

How is the Felkin-Anh model explained on a molecular orbital basis? Please include diagrams showing the orbitals involved and what exactly is being stabilised.

Also, if you can confirm (or unconfirm) my list of possible electron-withdrawing substituents, please do so in comments to the question.


texts: In what compounds does oxygen exhibit +½ oxidation state?

texts:
Theoretically it is said that the compound can show oxidation states in the interval $[n,n-8]$ where $n$ is the number of valence electrons.

Is there any compound in which oxygen shows +1/2 oxidation state. If so, then please provide an example.


texts: Mechanism for conversion of gem-dihalide to carbonyl compound

texts:
How does nucleophilic substitution work in a compound consisting of two leaving groups?

I understand that hydroxide ions will attack the carbon centre (which bears a partial positive charge) and cause a nucleophilic substitution reaction.

What I'm unsure of is whether the reaction proceeds via

The hydroxyl groups replacing the leaving groups one at a time (double $\mathrm{S_N2}$).
After the replacement of the first hydroxyl group, the repulsions between the electron pairs of oxygen and of chlorine cause the chlorine, a better leaving group, to leave, causing formation of a cation. ($\mathrm{S_N2}$ followed by $\mathrm{S_N1}$).
Both bonds forming at once (a transition state with six bonds to the center), although this seems very unlikely.


texts: How does a reference electrode work in a three electrode system?

texts:
This is what I understand about three electrode electrochemistry (correct me if I am wrong):

The working electrode is where the reaction of interest happens, e.g. copper ions reduced to solid copper.
The auxiliary/counter electrode supplies the current to the working electrode, i.e. it is the source of the electrons (maybe not in all cases?) e.g. zinc metal is oxidised to zinc ions.
The reference electrode lets you control the potential difference so you don't apply too much driving force to the working electrode and end up reducing water etc. No current passes through it.

I don't understand how the reference electrode lets you control the potential and how it works if no current passes through it. How is it connected to the other electrodes?


texts: Does anyone have experience with polycaprolactone?

texts:
I am trying to create an emulsion from polycaprolactone. My efforts thus far have resulted in unstable emulsions which sediment and coalesce after some time. This is what I have tried:
Dissolve 5g of PCL in 100 mL of acetone.
Add the PCL solution drop by drop into a 1% Tween 80 solution agitated at 5000 rpm using a homogenizer.
Remove the solvent using a rotavap.


texts: Why are dipoles "permanent/induced dipole permanent/induced dipole" and not just "permanent/induced dipole" once?

texts:
My teacher would always say "induced dipole induced dipole" and while it annoyed my slightly (as you were saying the same word twice) it didn't really bother me, but now looking through some exam papers it's called the same thing "induced dipole induced dipole", so why is it repeated twice? Would I be "wrong" for just saying "induced dipole" once? If so, what's the difference between the two?

(Sorry if this seems like a simple or stupid question, just I'm always curious and the internet doesn't really work for searches like this.)


texts: Why is Q/nF equivalent to the amount of substance in electrolysis?

texts:
I am told that

$$Q = nF$$

where $Q$ is the quantity of current, $n$ is the amount of electrons and $F$ is Faraday's constant. Since Faraday's constant is the charge carried by 1 mol of electrons, multiplying it by the amount of electrons to give the total charge makes perfect sense. But why does dividing $Q$ by $nF$ gives the amount of substance? Won't the answer just be 1 for all possible values?


texts: HOMO / LUMO energies in a qualitative view

texts:
I have a question regarding the HOMO and LUMO energies depending on various effects like substituents and electronegativity. It seems to be a somewhat known topic but I cannot really find a clear
answer anywhere that would just summarize those effects. So I started to wrap my head around various qualitative effects that you can attribute to either a large or a small HOMO-LUMO gap.

The easiest approach would therefore be considering Koopman's theorem, where the negative HOMO energy approximates the ionization potential and the negative LUMO energy approximates the electron affinity.
If we then move to Mulliken's definition of electronegativity we can see that the sum of both IP and EA (divided by two) serve as a good approximation to the electronegativity. Which means that upon many other effects the electronegativity
seems to be a key feature to describe the HOMO and LUMO energy. And this is also what I remember from lectures.

In my memory a more electronegative element will lower the energy of the LUMO. That is why in for example photocatalysis many conjugated heterocyclic (N-substituted) ligands are used. The lower π*-orbitals give rise to MLCT transitions.
On the other hand the HOMO energy should be increased as well.

If we move to the Klopman-Salem equation we can derive that according to HSAB concept a large HOMO-LUMO gap will be a pair of a hard acid and a hard base and a small HOMO-LUMO gap will be a soft-soft pair.
One simplification to this is the case of a Lewis-acid and a Lewis-base reacting, or an electrophile and a nucleophile. Here the HOMO of the nucleophile will interact with the LUMO of the electrophile.
This means that a high nucleophilicity requires a high HOMO energy. Unfortunately there is no good description besides lone-pairs on real nucleophilic strenght.

So I thought I could perhaps find other examples and therefore moved to carbenes and their analogues. We destinguish singulett and triplett carbenes. A singulett carbene has a larger HOMO-LUMO gap.
Moving to heavier elements we get more singulett character. But this can't be used here since this effect is due to more complicated effects. As Si-Si-bonds and double bonds tend to be be much more reactive and are easily photo-activated as well the HOMO-LUMO gap should be smaller than in corresponding C-C-bonds.
But what about substituents on the carbene? Here we find that electronegative ligands will stabilize the a1-orbital in the carbene and in for example aminocarbenes, the π-donor-function of the $\ce{NH2}$-group increases the energy of the b1-orbital.

So from these examples I would summarize that in general the inductive effect of an electronegative substituent will stabilize and therefore descrease the energy of the HOMO.
And a π-donor will increase the energy of the LUMO by destabilizing it.
Comparing this to ligand field theory I would conclude that having an alkyl group will destabilize and therefore increse the HOMO and a π-acceptor will descrease the energy of the LUMO.

Are my findings and ideas somewhat applicable and true? And are there other very simple effects that I can take into consideration if I want to describe the relative positions of the HOMO and LUMO?


texts:
The compound given is camphor:

We have to find the total number of stereoisomers for this compound. Now I can see two chiral carbons so I thought the number would be $4$ but it turns out that there are only $2$.

I can't quite see why. I realize that it is a bridgehead compound which would make it non-planar but how does that affect stereochemistry? Any help would be appreciated.


texts: Fuel cell potential for the electrolysis of ammonia

texts:
I am trying to calculate the fuel cell potential for the electrolysis of ammonia with the following equation:

E = Gibbs free energy for the reaction/(# electrons X Faraday's Constant)

The half reactions are as follows:

$$2NH_3 + 6OH^- -> N_2 + 6H_2O + 6e (Anode) E^0 = -0.77 V $$
$$ 6H_2O + 6e -> 3H_2 + 6OH^- (Cathode) E^0 = -0.83 V $$

I obtained the potencial values from the following paper and (double checked online as well): https://www.researchgate.net/publication/327875102_Review-Ammonia_Oxidation_Electrocatalysis_for_Hydrogen_Generation_and_Fuel_Cells
Equations (4a,4b and 4c)

The overall reaction is then:

$$2NH_3 -> N2 + 3H_2 $$ $$E^0 = +0.06 V $$ ** in the paper they seem to imply that the cell voltage is $$ + 0.06 V$$ which I don't understand why, since the oxidation takes place at the anode, therefore for the anode the potential should be $$ E^0 = +0.77 V$$ from my understanding.

I have doubled check my standard enthalpies of formation and entropies of formation. However, when I calculate the Gibbs free energy of the reaction I keep getting $$ E^0 = -0.06 V$$ for the overall reaction.
My Gibbs free energy is positive and the temperature I am using is 298 K, also NH3 is in a gaseous state. I have tried calculating the $$ E^0 $$ for $$ H_2 + 0.5 O_2 -> H_2O $$  and I obtain a cell voltage of $$ E^0 = 1.23 V $$ which corresponds to the reaction Gibbs free energy of $$ - 237 kJ/mol $$ , I just don't know where I am getting confused in the ammonia reaction.

In the paper they mention that the reaction is thermodynamically favorable, but I don't see how when the Gibbs free energy for the reaction is positive.


texts: How to experimentally measure number of protons or electrons in an element?

texts:
How can one measure the numbers of protons or electrons (the atomic number) in a substance?

Like if the element I examine is carbon I expect the result to be 6.

Preferable a simple experiment which can be done in the kitchen with kids attending (cheap and safe). Any atoms will do. A mass spectrometry is not available.


texts:
I'm using Checkmol/Matchmol for substructure determination and retrieval, and I'm having problems determining whether a given molecule is the substructure of another molecule when they have the same connectivity map.

I work in drug design so charges, isotopes, radicals and geometry are a very important concern.

Given the following molecules, for example:

+---------+-----------------+-------------------------------------+
| mol_id  | formula         | smiles                              |
+---------+-----------------+-------------------------------------+
|    7959 | C7H15Cl2N2O2P   | ClCCN(P1(=O)NCCCO1)CCCl             |
|   41041 | C7H15Cl2N2O2P   | ClCCN([P+]1([O-])NCCCO1)CCCl        |
|  572776 | C7H15Cl2N2O2P   | ClCCN([P@]1(=O)NCCCO1)CCCl          |
|  572791 | C7H15Cl2N2O2P   | ClCCN([P@@]1(=O)NCCCO1)CCCl         |
| 1742146 | C7H13Cl2D2N2O2P | ClCCN(P1(=O)NCC(CO1)([2H])[2H])CCCl |
+---------+-----------------+-------------------------------------+

You can see that connectivity map is identical in all cases, though some variations in stereochemistry, charges and isotopes can be found:

First question: "subestrcture" is a very wide term but I think about it as to whether is molecule A contained in molecule B, or not. Would you say all these are substructures of each other given they share the same connectivity map?

In a practical scenario, ignoring charges, isotopes and stereochemistry, every molecule in the example will be a substructure of eachother:

matchmol someMol.sdf someOtherMols.sdf

According to matchmol help (which is the only documentation on matchmol usage I could find), adding the isotopes constraint (-i) would exclude 1742146; adding charges constraint (-a) would exclude 41041; and adding geometry constraints (-gG) would exclude both 572776 and 572791... or that is what I would expect.

However, running the program for each molecule using all constraints results in the following:

matchmol -sGgaid someMol.sdf someOtherMols.sdf

7959  7959    T
7959  41041   F
7959  572776  T
7959  572791  T
7959  1742146 F
41041 7959    T
41041 41041   F
41041 572776  T
41041 572791  T
41041 1742146 F
572776    7959    T
572776    41041   F
572776    572776  T
572776    572791  T
572776    1742146 F
572791    7959    T
572791    41041   F
572791    572776  T
572791    572791  T
572791    1742146 F
1742146   7959    F
1742146   41041   F
1742146   572776  F
1742146   572791  F
1742146   1742146 T

Notice that, as expected, for the plain molecule (7959), neither 41041 (charged) nor 1742146 (with D isotopes) are a substructure; but both stereoisomers (572776 and 572791) are.

Interestingly, for the the charged molecule (41041), the same molecule is a substructure (bug?), but plain and stereo are.

Stereoisomers 572776 and 572791 should not be substructure of each other when geometrical constraints are in place, yet they are...

So... second question: Am I doing something wrong? Am I misunderstanding the results?


texts: Catalysts to accelerate foamy polyurethane reaction

texts:
This is the reaction that I am referring to:  https://www.youtube.com/watch?v=EoRUSo0BWC0

I am interested in finding catalysts to accelerate this fun chemistry demonstration. I have heard that some amide catalysts can accelerate CO2 production leading to faster foam rise, but I have not found any sources confirming this. Does anyone know of any catalysts to accelerate this fun chemical demonstration?


texts: Polymers with no molecular mass distribution?

texts: What sort of ideal conditions are required - theoretically - to conduct polymerization reactions to make all the macromolecules end up with exactly the same molecular mass, just like the products in normal chemical reactions? How do living organisms manage to synthesize macromolecules, for instance proteins, different than humans do in the lab?


texts: Three general questions in silanization of a glass surface

texts:
For silanization, I put a glass slide horizontally and pour the silan solution on it to cover the glass surface. Then I leave it for a specific time and then wash with water and acetone.

I have three questions:

Is this method correct or I should necessarily deep coat the glass plate into a container of silan solution (because in the 2nd method, there are larger number of available agents than can react with glass or have better accessibility to the glass surface)?
How durable is the silanized glass? i.e. after silanization, when I want to clean the glass surface from reaction products, can I rub something onto the surface to help clean it better or the treated layer of glass might be damaged? (rubbing with cleanex, etc)
For getting maximum hydrophobicity, can I use Octadecyltrichlorosilane>90% directly on glass surface (for how much time?) or I should dilute it?


texts:
Methane is a non-polar compound, i.e. it shows no bipolar movement but even after that it reacts with water which is a polar compound and polar and non-polar compounds do not react. Why does this reaction take place, then:

Q: The reaction of methane and water is a way to prepare hydrogen according to
$$\ce{CH4 (g) + H2O -> CO2 (g) + H2 (g)}$$
...


texts:
The amount of heat required to vapourize one mole of a liquid at
constant temperature and under standard pressure (1 bar) is called its
standard enthalpy of vapourization.
The enthalpy of vaporization is often quoted for the normal boiling
temperature of the substance.

Suppose, some amount of water is kept inside a perfect thermally conducting container at 1 bar pressure and $\mathrm 50~^\circ \mathrm{C}$ within a thermal reservoir of $\mathrm 50~^\circ \mathrm{C}$ also. Due to evaporation, slowly liquid will convert to vapours.
After one mole of water evaporates, if we measure the heat energy received by the container from the reservoir, would it be equal to standard enthalpy of vapourization of water at $\mathrm 50~^\circ \mathrm{C}$?


texts: What is the mechanism of trialkylborane oxidation with hydroperoxide?

texts: This is the mechanism of trialkylborane. In this mechanism I can't understand why should the -OH group leave and the -R group enter in its place to form borate ester. Can someone please explain me that step?


texts: In the periodic table, why doesn't the 2nd row have exactly 2 elements?

texts:
Row 1: 2 elements

Row 2: 8 elements

Row 3: 8 elements

Row 4: 18 elements

Row 5: 18 elements

Row 6: 32 elements

Row 7: 32 elements

In other words: 2, 8, 8, 18, 18, 32, 32

Why does the first row have only 2 elements, but all the next rows have a pattern? There's a pattern of two rows having the same number of elements that only starts after the first row.

EDIT: I just noticed this alternate periodic table! It's first two rows have two elements each! Why does it work there? (I can't interpret the s, p, d, f part on the left). Which one is the right periodic table?


texts:
I am using ED-XRF for geochemical analysis for a geology dissertation. The ED-XRF provides a ppm reading for elements and a 2sigma error, for example 472 +- 5.11ppm Sr.

An example calibration curve made for Sr comprising 37 standards has a linear regression of y=1.26x + 32.1 (R^2 0.9991), which I can easily apply to correct my unknown analyses. I need to plot my corrected readings with their error bars, so how is the 2sigma error associated with this unknown calibrated?

Does this error value also simply get calibrated with the curve equation, or just the slope value, or is this error propagation far more complex? I have searched for a solution and keep finding an equation for uncertainty propagation with calibration curves, but this only calculates the uncertainty caused by the curve, and has no relation to the uncertainty of each analysis? So is the total error the original 2sigma error provided by the machine + calibration curve uncertainty?

Thanks


texts:
The particle on a ring is a useful model for the motion of electrons around the porphine ring, the conjugated macrocycle that forms the structural basis of the heme group and the chlorophylls. We may treat the group as a circular ring of radius $\pu{440 pm}$, with 20 electrons in the conjugated system moving along the perimeter of the ring. Assume that in the ground state of the molecule quantized each level is occupied by two electrons.
(a) Calculate the energy and angular momentum of an electron in the highest occupied level.
(b) Calculate the frequency of radiation that can induce a transition between the highest occupied and lowest unoccupied levels.

How do you calculate HOMO and LUMO given that 20 $\pi$ electrons exist? Writing the electron configuration of the ground state molecule seems too lengthy.


texts:
I was researching for a question that asked me to find a ratio of temperatures, and I came across this, which would help me greatly:
Since, most of the temperature changes occur during the isochoric (2–3) and isobaric processes (4–1), a constant specific heat can be assumed during the isentropic processes (1–2 and 3–4).
The total entropy change in the cycle must be equal to zero, therefore
$T_2T_4^k=T_3T_1^k$
where k is the rerversible adiabatic index.
But, I don't understand why due tho these factors this equation is true. Is there any clarification as to why this is the case?


texts: Is phosphoric acid to be considered a hazardous waste?

texts:
I've found some English sites proclaiming phosphoric acid to be used for porcelain cleaning and e.g. clogged drains, even though I mainly bought it to use to clean coffee makers and water kettles.

In my country (Finland) phosphoric acid can be found from the list of hazardous waste. However, there are contradictory views regarding whether phosphoric acid can be poured in to the sewer or not. If it's a hazardous waste, then it shouldn't. But I have this English resources saying that it can.

Should I abide by the local rules saying that it's a hazardous waste or is there a reason to believe it can be used safely e.g. in clogged drains or for cleaning the toilet?


texts: When can I use concentrations instead of activities in equilibrium calculations?

texts:
To calculate an equilibrium constant, it is said that you should actually use activities $a_i$ instead of concentrations $c_i$. But it is also said that within a certain range, you can use concentrations instead. This is also what is usually done because it's easier.

So what is this range? When can I safely use concentrations and when should I definitely switch to using activities?


texts: In regard to collision theory, why do molecules have to have the correct orientation in order to react?

texts: Hypothetically speaking, if a reagent in a bimolecular reaction has enough energy to break the bond of the other reagent but is orientated in the wrong direction, why does the bond not break? Does the reagent's orientation affect the activation energy of the reaction somehow? The point I'm trying to make is if you have enough energy to break a bond, why would molecular orientation matter when the same amount of energy is being used to distort bonds regardless of orientation?


texts: Relative strength of metal hydrides as reducing agents

texts:
Question:

Out of $CH_4, CaH_2, FeCl_2$ and $BeH_2$, which compound would produce the most strongly reducing aqueous solution?

Thoughts:

Out of the hydrides, I would say that $CaH_2$ stands a good chance at being the strongest reducing agent, since the Ca-H bond energy is lowest (allowing the extremely reducing hydride to be released more readily into solution). The only rationale I can think up for this is the relative sizes of the other ion in the hydrides (Ca>Be>C) which implies that bond length is greatest in the calcium hydride (thus bond energy is lower). I am unsure as to how I should tackle the chloride compound. Much assistance is needed.


texts: In a paper about the modes of action of DNMT, it said there an increased flow of electrons to carbon 5 following the formation of a covalent bond between DNMT and carbon 6 on cystine. Why is this? What is the effect of the flow of electrons?


texts:
I am trying to form an enamine, and I was trying to figure out if the following reaction is possible:

Would this reaction terminate after the formation of the shown product, or will the other carbonyl also react, producing a final product with two enamine groups? If so, is it possible under any conditions to stop the reaction after the formation of the first enamine?


texts:
I have the following IR Spectrum that I am trying to interpret:

So far I am thinking this compound have:

a primary amine due to two peaks at 3624 and 3533.
The sharp peak 3416 could indicate an alkyne(sp C-H).
And the other sharp peak at 1716 is an aldehyde or ketone.

Is this analysis correct ? And what have I missed ? Thanks for any help !


texts: The addition reaction between alkene and gaseous hydrogen bromide: why is it an addition reaction, rather than electrophilic addition?

texts: I have come unstuck on why - despite the fact that hydrogen bromide is a polar molecule - why it does not react with ethene via electrophilic addition in its gaseous state? For example, bromine reacts with ethene by becoming an induced dipole and then reacting via electrophilic addition. Why does H-Br(g) not? Is is to do with boiling temperature?


texts:
According to a web site about health (Antranik):

  The oil that naturally comes from our skin is a type of cholesterol.
  Whenever we stand under direct sunlight, the ultraviolet rays react
  with this oil.  The ultraviolet radiation breaks some chemical bonds
  in the oil so that it forms a different molecule.  This molecule is
  known as the infamous Vitamin D3 which is why it’s also called the
  “sunshine vitamin.”

According to the web site, cats lick this converted oil off their fur to get Vitamin D (cholecalciferol).

What exactly is the reaction here? How could UV radiation be converting oil into a hormone? I thought hormones were much more complex molecules than oils, not simpler molecules.


texts: Why is atomic number is more or less the same as number of neutrons for light elements?

texts: In periodic table, the atomic weight is more or less twice the proton number. Do neutrons naturally tend to be in similar quantity as protons? I know atomic weight weighted average of isotopes but why this more or less a trend if we move across the periodic table we find atomic weight is 2(protons) + $\epsilon$ where $\epsilon$ < 2


texts: Would electrolysis work with a conductive (but waterproof) divider between anode and cathode?

texts:
Note I am not trying to "double fuel efficiency" in a car or something scamey like that. My purpose is to fill balloons with hydrogen and possibly power an HHO torch (also make it safer because pure hydrogen or pure oxygen will not explode).

I found this https://www.thingiverse.com/thing:1200458 HHO generator someone made which seems perfect for my needs except that it outputs HHO together. I cannot find a design for actually useful HHO production that actually separates H2 and O (by useful I mean large volumes of gas, not just a science experiment).

My plan for alterations is to make that design thicker so that it can hold two arrays of plates and split it in halves. I would also add in separate nozzles for each side. I would then print both halves and glue them together with a metal plate (aluminum) in the middle. Would this work? I don't see why it would not however I have not seen a design like this which probably means that I'm wrong rather than everyone else :D


texts:
Why is this type of resonance not possible? My book says that the positive charge is localised, and resonance is not possible.

But I have drawn the resonance structures (though you can note that the last resonance structure can be obtained directly without disturbing the positive charge). Are the other structures not possible? It not, why?

Aromacity is not disturbed as all the structures have cyclic resonance and follow Hückel's rule. Please explain.


texts:
The hair gel is called "lets Jam Gel". It says it uses micro emulsion technology.
What chemicals can you use to break it down or undo the bonds?

I'm trying to get it out of my head. I washed my hair with T sal and cut my hair off but it still grows back patchy and easy to style like it has gel in it. I think it may be in the epidermis or even dermis by now.

ingredients: 42692 SS11 - Aqua / Water Isocteth-20 Paraffinum Liquidum / Mineral oil Glycerin Oleth-2 Propylene Glycol Parfum / fragrance Sorbic Acid Methylparaben DMDM Hydantoin Ethylparaben Limonene Hydroxycitronellal Geraniol Amyl cinnamal Linalool Simethicone CI 19140 / Yellow 5 CI 14700 / Red 4, CI 172200 / Red 3. F.I.L D45949/1


texts:
I have been looking at this diagram from quite some time, I know the 18 pi electron cycle that forms porphin(e) is definitely planar but what about the whole molecule?... The Nitrogen's act as a polydentate ligand with a metal complex so that may be a reason that the whole molecule may not be planar..
Can someone elaborate?


texts: Metallic and magnetic nature of transition metal oxides

texts:
Which of the following oxides is both metallic and ferromagnetic:
  $\ce{VO2}$, $\ce{CrO2}$, $\ce{MnO2}$, $\ce{TiO2}$?

This is how I went about solving it:

Since ferromagnetic materials also show paramagnetism, so the condition for paramagnetism must be checked.

In $\ce{TiO2}$, $\ce{Ti}$ has no unpaired electrons, it cannot be paramagnetic and as a consequence it cannot be ferromagnetic.

$\ce{CrO2}$ is amphoteric. A metallic oxide would show basic properties in most cases. So $\ce{CrO2}$ may not be the right answer.

$\ce{VO2}$ is basic. All three except $\ce{TiO2}$ are paramagnetic.

Then I googled, I didn't get an exact answer. But I read that $\ce{CrO2}$ is termed as a "half metal" which is related to its magnetic properties, most part of which I didn't understand.

Then I also found articles about half metallic ferromagnetism of $\ce{TiO2}$. But that goes against my assumption.

So my questions are:

  Explain where I'm wrong.
  Why $\ce{CrO2}$ is the answer? (Found that when I finally referred to the solutions of the question paper. However the solutions given
  can have mistakes. So it is possible that $\ce{CrO2}$ may not be the
  true answer).
  If you think $\ce{CrO2}$ is not the answer, then why?


texts: How would one disassociate the carboxylic acid on the end of a perfluorooctanoic acid molecule?

texts:
This is what a perfluorooctanoic acid molecule looks like. The carboxylate head on the end would normally disassociate in water because carboxylic acids are weak, but because of the fluorocarbon tail, the molecule is very stable. How do you remove the head from the rest of the molecule? Could you use UV radiation to perform homolytic fission for the decarboxyliation?

To provide some context, this molecule is used in flame retardants, and those flame retardants are polluting drinking water reservoirs. The head of this molecule, once the pollutant is inside the body, binds to proteins and behaves like hormones, disrupting normal hormonal function.


texts:
Uranyl formate has a structure something like:

$\ce{UO2-(OCHO)2}$

So the structural formulae I've seen have two double-bonded oxygens directly attached to the U and each formate group is attached by single bonds to the oxygens. Like this.
The empirical formula for the dry powder is written as a monohydrate.

Can someone explain how this thing gets solvated in water and what the solvated ions are, exactly? I just realized I was assuming it dissociates into a 'uranyl' ion (whatever that looks like) and two formate ions$\ldots$but then I'm confused about where the formate's oxygen goes.


texts: Arterial blood CO2 content, division and partial pressure

texts:
My lecturer cites Boron and Boulpaep's Medical Physiology (2nd edition) for the following claims:

the total $\ce{CO2}$ content of arterial blood is $26.4$ mmol/L or $48\%$ v/v (not sure if these numbers convert)
including $90\%$ as bicarbonate, $5\%$
as dissolved gas and 5% as carbamino compounds (specifically
carbaminohaemoglobin)
the arterial partial pressure of $\ce{CO2}$ is $40$mmHg

How does one get from the arterial partial pressure value to determining these proportions and figures?

What I've tried: Henry solubility constant for $\ce{CO2}$ in water, equilibrium constants for the hydration of $\ce{CO2}$, ionisation of carbonic acid, assumed carbaminohaemoglobin formation went to completion and only consumed $\ce{CO2(aq)}$. Still don't seem to completely match my lecturer's figures.


texts: Why is it advised to put a Styrofoam plate under an Erlenmeyer flask?

texts:
At school today, we were doing experiments with ammonium nitrate and sodium hydroxide, and mixing them with water into an Erlenmeyer flask (separate flasks, of course). My instructor told us that we had to keep a Styrofoam plate under the Erlenmeyer flask at all times.
After the experiment, she told us to find out why we put a Styrofoam plate under the flask by tomorrow or we would get a 0 on that assignment.
Does anyone know why? I'm thinking it's to protect the table from the heat or coldness of the flask, or to protect the table in case of spills. We have to get the question exactly as she wants it, so I am looking for help.


texts:
Why is mercury the only metal that is liquid at room temperature?

Note: I am a high school student and would appreciate an answer, if possible, suited for my level of understanding.

Thank you.


texts:
Are the following equivalent structures for 2,2-dimethylpropane?

I think so, because my rendering simply rotates the cross 45 degrees!

Also, regarding 3,3-diethylpentane, are these both equally valid structures? My rendering seems to look way different but filling in the carbons and hydrogens, both appear correct:


texts: Why are higher oxides of non-metals more acidic?

texts: I have studied that if the electronegativity difference between O- and element M is more then it is a basic oxide and if the difference is less then it is an acidic oxide. However, it is a fact that higher oxides of Non metals are more acidic than lower oxides. If the theory concerns polarisation, is it not contradictory?


texts: Does the "Bat Gen" claim to produce more energy than it uses?

texts:
The following links claim that inventor Arturo Solis Herrera has created an "everlasting battery".

http://www.mexiconewsnetwork.com/news/bat-gen/
http://www.faqs.org/patents/app/20090134007#ixzz10Sh9iLQM

The article claims that:

  Bat gen is the name of this ever-lasting battery. It consists of a biochemical process triggered by mixing water and melanin, which results in a substance capable of separating oxygen from hydrogen (the components of a water molecule), therefore liberating energy.

  The process continues as the same molecule brings together both elements turning them into water again; as a result one more energy load is triggered.

  According to Solis’ research, once this process is reached, it can continue for 100 years! Moreover, there are several ways of artificially producing the melanin found in human nails, hair and retina; two of them, which he already patented, are based on vegetables and oil.

Although they do not claim that the battery is perpetual, they seem to imply that mixing water and melanin can give an (oscillating?) reaction that can last for 100 years, providing cheap power.

Does this have any chemical basis? What matter is consumed?
Would that work without the user needing to add anything to the battery or is the article just describing the process in a misleading way?


texts: The absolute entropy of $\ce{H^+ (g)}$  is  $\ce{108 kJ/mol.K}$. However, the absolute entropy of $\ce{H^+ (aq)}$ is exactly 0. Why is that? Also, the standard enthalpy of $\ce{H^+ (aq)}$ is 0, so what is it the standard state of?


texts: In coordination chemistry, we classify ligands as sigma donors, pi acceptors and donors. Benzene is a pi donor, as is the cyclopentadienyl anion, but do these two possess any pi acceptor character? (Can a ligand be both pi acceptor and pi donor?)


texts:
Would the reaction between zinc and sulfur be

$$\ce{Zn_{(s)} + S_{(s)} -> ZnS_{(s)}}$$
or
$$\ce{8 Zn_{(s)} + S_8\ _{(s)} -> 8ZnS_{(s)}}$$

I know that $\ce{S}$ and $\ce{S8}$ are allotropes of sulfur, but which one should I use for a reaction with sulfur at room temperature?


texts: What is θ in Bent's rule equation (%s - character)?

texts:
I was learning about Bent's Rule. I came across a formula
$$\cos\theta = \frac{s}{s-1}$$
I am quite confused about $\theta$. I know that it represents bond angle. But for a compound like $\ce{PCl5}$, which bonds angle has to be considered? For the equatorial bonds, $\theta = 2 \pi/2$ was used and $\theta = \pi/2$ was used for axial bonds. My doubt is that why we are not using $\theta = \pi/2$ for equatorial bonds as they also have form $\pi/2$  angle with with axial bonds.
I asked my mentor about this. He said that $\ce{PCl5}$ has non-equivalent hybridization and $\mathrm{sp^3d}$ is actually $\mathrm{sp^2 + pd}$. The equatorial bonds are $\mathrm{sp^2}$ hybridized and have bond angle as $120^\circ$. The bond angle for axial bonds is the angle formed by the axial bond and the plane formed by chlorine atoms which connected to phosphorus through equatorial bonds.
After this, I became more confused. Can anyone please tell me the meaning of $\theta$ in the formula? Is it really the bond angle? If yes, then which angle has to be considered in $\ce{PCl5}$ and why?


texts: How to monitor (high) oxygen content in gas (air)?

texts:
How could I go about monitoring (semi-continuously, say, one measurement per 10 minutes) oxygen content in an oxygen-rich air mix (air with substantial amount of nitrogen removed with a Zeolite filter)?

There are questions (1, 2 ) about measuring oxygen content in air, using a candle and checking volume after burning. Them being cumbersome is less of a problem - worse that lighting a candle in 80+% oxygen atmosphere can a be quite... energetic reaction.

Are there any other reactions that can provide oxygen content measurements like that, preferably not involving open flame?

(Neither accuracy nor measurement time are very important, but the measurement should be easy to perform, and repeatable, no large amounts of expensive consumables. Something that could be automatized would be nice.)


texts: Free API to view 2D representation of Molecules

texts:
I'm looking for a free API that can accept a SMILE and produce the 2D structure of a molecule. I would like to include this in a web page.

I have collection of SMILES and would like to have the 2D structure available as part of a database. I tried generating images using RDKit but I can't add that these images to any data frame or tabular data structure. Any suggestions on how to display the 2D representation of and any SMILE queried on the web page will be appreciated.


texts: Why does p-dichlorobenzene have zero dipole moment while hydroquinone does not?

texts: At first I thought that both the OH groups would cancel out their dipole moments in hydroquinone. On reading further, I realized that because of the two different planar structures possible, it has a non-zero dipole moment. My textbook says the dipole moment of para-dichlorobenzene is zero. But by the same logic we used for hydroquinone, shouldn't this have a non-zero dipole moment as well?


texts:
In nitrosobenzene, there are two ways that the $\ce{-N=O}$ group can show mesomeric effect.

  It can show positive mesomeric effect by becoming $\ce{=N+=O}$
  It can show negative mesomeric effect by becoming $\ce{=N-O-}$

  So will the electron density on the benzene ring increase or decrease?

I think it should decrease because in the first case we have a $\delta^+$ charge on nitrogen and a $\delta^-$ charge on carbon, and in the other case we have a $\delta^+$ charge on carbon and a $\delta ^-$ charge on oxygen.Is this reasoning correct? Or will there even be such an decrease?


texts: Why do chloroform and benzene exhibit negative deviation from Raoult's law?

texts: Chloroform is a polar molecule, and benzene is nonpolar. Shouldn't the chloroform-chloroform and benzene-benzene intermolecular forces be stronger than chloroform-benzene interactions (like dissolves like), which would result in a positive deviation from Raoult's law?


texts: What happens when FeF3 is reacted with benzene?

texts:
My text book says that halobenzenes can be prepared by aromatic substitution on benzene ring by using Fe or FeX3 as Lewis acid but this method isn't useful for preparation of fluoro benzene because of it's high reactivity.
My question is what will be the product if FeF3 is reacted with benzene, I tried searching a bit on internet but couldn't find anything helpful.


texts: Sodium permanganate from manganese dioxide and sodium hypochlorite

texts:
This page states that sodium permanganate can be formed by the reaction of manganese dioxide with sodium hypochlorite and sodium hydroxide:

$$\ce{2 MnO2 + 3 NaClO + 2 NaOH -> 2 NaMnO4 + 3 NaCl + H2O}$$

I assume sodium carbonate ($\ce{Na2CO3}$) will also function in this reaction as a substitute for $\ce{NaOH}$.

Does this reaction take place at standard conditions, or are increases in temperature/pressure etc. required? Approximately how long will it take (at STP)? Also, will sodium carbonate be sufficient, or is sodium hydroxide required?


texts: TD-DFT transition dipole moment vector does not align with experimental data

texts: I have been modelling excited states of some molecules with similar stucture using TD-DFT theory, however, I have encountered an issue that sometimes transition dipole moment does not align with the direction of experimental. For example, for molecule 1 the right direction of a transition dipole moment is with B3LYP functional and CAM-B3LYP functional results in a dipole moment in an opposite direction (the results were independent of the basis set). For molecule 2 the B3LYP functional yielded worse results than CAM-B3LYP. What could be the issue? I have done explicit geometry optimizations and frequency calculations (no imaginary frequencies were found) for each functional and basis set.


texts: Spontaneous Reaction and Gibbs Free Energy

texts:
I know how to derive the expression for the equilibrium constant starting from $\mathrm dG=0$,
$$\ln(K)=-\frac{\Delta G ^\circ}{RT}$$

However, if we are not at equilibrium, $\mathrm dG$ is not necessarily zero. In this case:
$$\frac{\partial G}{\partial \epsilon} = \sum \mu_i \nu_i = \Delta G ^\circ + RT \ln \left( \prod a_i ^{\nu_i} \right)$$

Where $\nu_i$ are the stoichiometric coefficients, $\mu_i$ are the chemical potentials, $\Delta G^\circ$ is the Gibbs free energy of reaction at standard state and $a_i$ are the activities.

Hence,
$$\frac{\partial G}{\partial \epsilon} = RT \ln \left(\frac{Q}{K} \right)$$

Where $Q=\prod a_i ^{\nu_i}$ is the reaction quotient.

So the question is, if we want to kown if a reaction is spontaneous, do we look at the ratio $Q/K$? If this is correct, if $Q > K$ then $\frac{\partial G}{\partial \epsilon} > 0$ and the reaction would be non-spontaneous, whereas if $Q < K$ then $\frac{\partial G}{\partial \epsilon} < 0$ and the reaction is spontaneous.

If so, if we start with reactants only, $Q=0$ (since the activites of the products are zero because there are none) and the reaction would be spontaneous, and we would always get at least a little bit of products.

However, various pages in internet say that if $\Delta G ^\circ < 0$ then the reaction is spontaneous, and it is not if $\Delta G ^\circ>0$.

So how do you know, then, if you start with only reactants, if a reaction is going to happen?


texts: Is the aromaticity broken in some resonance structures of para-nitro-aminobenzene?

texts:
According to my course of organic chemistry, para-nitro-aminobenzene has to break his aromaticity to delocalize the electrons of the amino-group in the nitro-group.
I don't really see this, when I draw the resonance structures.


texts:
This is a question from the last year's semester examination.

  Why is Trouton's rule not valid for liquids with boiling  points less
  than 150 K?

I searched the internet but only found that the exceptions mentioned include liquids with strong intermolecular attraction like hydrogen bonding and some similar cases. Can anyone give me a proper answer?


texts: What is the mechanism for demercuration?

texts:
The following image is from 'Organic Chemistry Second Edition' by Clayden, Greeves, and Warren.

The final step is the demercuration, but I'm unable to find a definitive mechanism.

The wikipedia page lists a mechanism sourced from the Journal of the American Chemical Society:

Wikipedia Page for Oxymercuration

But I've found videos on YouTube which outline an SN2 displacement of the acetoxymercuri group by hydride. e.g.: Mechanism of Oxymercuration Demercuration (new)

So I would like to know which mechanism is correct.


texts: What would be the reaction equation between ammonium nitrate and a powdered metal?

texts:
The SDS for ammonium nitrate says it will react with powdered metals spontaneously. What would be the reaction equation, say with iron or copper?

This mixture is used in various pyrotechnics, and it is intentionally allowed to combust with heat and shock, but how does the reaction proceed spontaneously as described in various SDSs in the absence of any ignition source? Is this due to the mix attracting small amounts of water, allowing the nitrate to attack a metal instead?

Would the theoretical products always just be various oxides of the metal involved?


texts: Why do principal energy levels in an atom get closer together as n increases?

texts:
The title says it all. Reasons that I can supply include: increased nuclear charge increasingly catches up in terms of influence to the increasing shielding and proof by contradiction in that if the space remained the same there would be negligible nuclear pull on the valence electrons and so this must not be the case. What is a comprehensive explanation for why this phenomenon is so?

Thank you!


texts: Why does lithium aluminium hydride reduce a ketone over enolising the ketone?

texts:
By lithium aluminium hydride enolising the ketone, hydrogen gas is produced.

This is very entropically favourable, so why does this not happen and rather we get addition of the hydride ion to the carbonyl?


texts: Do polar compounds travel further or less far than unpolar ones in hexane/ethyl acetate TLCs?

texts:
Would ethyl acetate/hexane be considered nonpolar or polar overall? I know that the ethyl acetate is polar and the hexane is nonpolar. I am trying to understand what if polar or nonpolar analgesics would travel further in TLC. I know that if  ethyl acetate/hexane is polar than a more polar one will travel further, and if it is nonpolar then nonpolar will travel further.

I was looking here and I see that caffeine is the most polar (out of aspirin and acetaminophen) and traveled the least distance (lowest $R_\mathrm{f}$) in my experiment. I thought that ethyl acetate/hexane was polar so I would have thought caffeine would be the least polar since it traveled the shortest.

So am I wrong that  ethyl acetate/hexane is polar or are they wrong that caffeine is the most polar?


texts:
It's there in every high-school textbook: $\ce{O2}$ is the supporter of combustion. Without $\ce{O2}$ combustion cannot take place. Why? And why only $\ce{O2}$? Why not some other element?

And, what happens when a combustible gas burns in air? Say $\ce{H2}$?


texts: What's the relationship between Van der Waals forces and hydrophobic interactions?

texts:
A question on a past exam for a course I'm studying for asks:

  What's the relation between Van der Waals forces and hydrophobic
  interactions?

From what I understand, Van der Waals forces are just a name to summarize a bunch of little weak forces that only come into play when molecules are placed close to one other, based off this previous answer to my question.

I understand that hydrophobic interactions arise because non-polar components of a molecule are unable to form bonds with hydrogen in water, but disrupt the hydrogen, forcing them to make a cage-like structure (although I'm not clear on why), based off this entry in the Chemistry wiki.

Is the relation between these two forces that Van der Waals forces can be encouraged by hydrophic forces? Is there some other relation I'm missing here? Does it have something to do with the interactions denaturing at high temperatures?


texts: Stability order of p-quinone, o-quinone and diphenoquinone

texts:
Question

Determine stability order:

Answer

 1 > 2 > 3

Thoughts
I found this question quite tricky and confusing. According to my concepts and logic

3 should be non-aromatic, while 1 and 2 are antiaromatic.
Also there is a lone pair repulsion in 2.

After racking my brain I up came with the answer of 3 > 1 > 2 (arguably most convincing for me), which is wrong according to the actually given answer.
So, while my answer for 1 > 2 is correct, I still have no explanation for 3.
Kindly help me on what I am missing or if I am wrong somewhere.


texts: What is the absolute configuration of carbon 5 in 5-bromo-2-methylhex-2-ene

texts: I am trying to work out the absolute configuration around carbon atom 5 in 5-bromo-2-methylhex-2-ene. Could someone please let me know if my working is correct? Does the wedged bond from C4 to C5 affect the structure of the molecule and its configuration?


texts: How can I determine the amounts of potassium bicarbonate and potassium sulfate in a solution?

texts:
I have an aquaeous solution of potassium bicarbonate and potassium sulfate. I want to find out the proportions of both compounds in the solution. What would be an efficient procedure?
Note that I do not have an analytical balance or other fancy equipment. I can do simple procedures like titrations.
One idea I had is that I could titrate it with an acid of known molarity. That would react with the potassium bicarbonate and when the pH became neutral as shown by an indicator, that would tell me how much KHC03 I had.
The sulfate is a more tricky problem.


texts: Why no thermal expansion for camping tents?

texts:
I know that solid materials expand when heated, which is called thermal expansion.

But what is happening to tent square or tent canvas of (plastic?) camping tents? I have noticed, that during the day, when it’s hot, there is a lot of tension in the skin of a tent. But when it gets colder (when raining or during the night), the tension is less and the fabric gets sloppy.

What is the reason?


texts:
When dealing with determining the ground state energy of a system, people often say that it is better to know the energy difference rather than the absolute minimum energy. I understand that the absolute minimum energy depend on the model so the more complex your model, the lower or closer the energy you found to the true ground state energy.
But what do people refer to when they say energy difference here? Different between what energies exactly?


texts: Writing a chemical equation with a reactant of unspecified chain length

texts:
Would appreciate it if I got some general tips and hints and not the solution cause I'm trying to learn from this question :)
The question is as follows:

FA1 is a solution containing $\pu{5.00 g dm-3}$ of a dibasic acid, $\ce{HOOC-(CH_2)_n -COOH}$.
FA2 is a solution containing $\pu{5.00 g dm-3}$ of $\ce{NaOH}$.
$\pu{25.0 cm3}$ of the acid solution FA1 needed $\pu{17.0 cm3}$ of the sodium hydroxide solution, FA2, for complete neutralization.

Determine the value of $n$ in the formula of the acid.

The issue I have is in starting the question. I genuinely have no clue how to start a chemical equation with something like $\ce{HOOC-(CH2)n -COOH}$. Tips and hints would be greatly appreciated thanks.


texts: Why does a mixture get warm in an exothermic reaction?

texts: The production of ethanol by fermentation is exothermic. My textbook says that the yeast stops working if the mixture gets too warm. Why would the mixture get warm if the reaction is exothermic?


texts: pH calculation - adding distilled water after titration

texts:
Will someone help me figure out how can I solve the following question?

We are given 110 ml of acetic acid (pKa=4.76), with concentration of 1M, to which we add 10 ml of NaOH with concentration of 1M.

Afterwards, we add the solution to 880 ml of distilled water.

What would be the pH of the solution, after the addition of water?

Will you please help me figure this out?

I obviously need to use Henderson-Hasselbalch here, but how does the addition of water change things?

Thanks a lot in advance


texts: Took a pic of the paper I tried it on it on, has the exact problem description written at top, and what I tried. Figured that would be easier then typing all that. The answer is supposed to be 2.0.


texts: Are all enolised molecules called enolates?

texts: From what I've gathered in my lectures, enolates are enolised cabonyl compounds. However e.g. a nitrile with an H on the alpha C can undergo enolisation. Is the resulting molecule called an enolate or an enolate equivalent, or something else?


texts: Where can I get potential energy surface for simple molecules?

texts:
I'm looking for potential energy functions for simple molecules, such as water or hydrogen sulfide. I only need the region around the equilibrium geometry, preferably as a Taylor series expanded in terms of normal mode coordinates, with mixed terms given to the fourth or higher order. Just the ground electronic state would do, but ideally I need the first excited state as well.

If these data isn't available, I'd appreciate if you could explain how I could obtain them myself (including software recommendations), given that I'm an undergraduate, who understands the theory but doesn't have much practical experience yet.


texts: Should titration stop at the intermediate color or a drop past the intermediate

texts:
Using Bromcresol green as an indicator, should one stop when the blue color changes to green or to yellow for more accurate results.

Shouldn't one aim to get a green because its far closer to the end point than a yellow could be. For example, if the solution turned yellow and an additional drop was added, it would be indiscernible.


texts: What is the ground state electron configuration of isoprene?

texts: Also the electron configuration of isoprene at its singlet state and also that of the triplet state?


texts: How many grams of sodium phosphate must be added to precipitate as much of one ion as possible?

texts:
Problem text:

Solid sodium phosphate is slowly added to $\pu{200 mL}$ of a solution containing $\pu{0.002 mol}$ of aluminum chloride and $\pu{0.001 mol}$ of calcium chloride (assuming no volume change occurs). How many grams of sodium phosphate must be added to precipitate as much of one ion as possible, while the other ion just does not precipitate? What percentage of the ion that will precipitate first is still left in the solution at that time?

My approach:

Two salts will be produced as the reaction goes: $\ce{AlPO4}$ and $\ce{Ca3(PO4)2}$

$K_\mathrm{sp} (\ce{AlPO4})=9.83\times10^{-21}$ and $K_\mathrm{sp} (\ce{Ca3(PO4)2})=2.07\times 10^{-33}$

Therefore, I can conclude that $\ce{Ca3(PO4)2}$ will precipitate first.

I need to find concentration of $[\ce{PO4^3-}]$ via
$$[\ce{Al^3+}][\ce{PO4^3-}]=K_\mathrm{sp}$$
$$[\ce{Al^3+}]=\frac{\pu{0.002 mol}}{\pu{200 mL}}=0.01M$$
$$[\ce{PO4^3-}]=\frac{9.83\times 10^{-21}}{\pu{0.01M}}=9.83\times 10^{-19}$$

Then I can find $m_\ce{Na3PO4}$ via finding number of moles first and multiplying by molar mass:

$$n_\ce{Na3PO4} = [\ce{PO4^3-}]\times V = 9.83\times 10^{-19}\times \pu{200 mL} = 1.966\times 10^{-19}$$
$$m_\ce{Na3PO4} = n_\ce{Na3PO4} \times \mathrm{Molar Mass} = \pu{3.22\times 10^{-17} g}$$

At this point, my result does not make much sense to me because the mass I obtained is extremely small. Unfortunately, I do not have the correct answers for that task, therefore, I would highly appreciate any help that can be useful in spotting mistakes I made in the solution.


texts: Why do strong acid-weak base reactions "essentially go to completion"?

texts: This is what my textbook says. I understand that the strong acid would readily donate a hydrogen ion, but I can't see how all the weak base will readily accept it (at least not to "essential completion").


texts: What is the mechanism behind the formation of phosgene from tetrachloroethylene

texts:
Tetrachloroethylene used to be a popular automobile brake cleaner. Unfortunately, when applied to hot brake rotors, it can turn into phosgene. This has resulted in many injuries and even fatalities.

  At temperatures over 315 °C (599 °F), such as in welding, tetrachloroethylene can be oxidized into phosgene, an extremely poisonous gas.

What is the mechanism behind the oxidation to phosgene? I know that these things probably happen--alkene bond is broken and oxidized--but is there a detailed mechanism?


texts: When you fill a bath, Is it different that you fill it directly or non-directly?

texts:
Yesterday I was taking a shower that this thought occurred to me that when you are filling a bath, flask, etc with water in two different ways in specified time, Will the amount of water in bath be different?

I did a experiment myself in 'Crocodile Chemistry' and got these results as seen below:

First level was pouring water from a faucet directly to the bath from a specified height for 10 seconds. The result was that approximately 250 cubic centimeter water was poured into it.

Second level was pouring water from a faucet to a 'already filled beaker' and filling the bath with overflowed water of the beaker at the same height and the same time. The result was similar to the first level.

I saw all these but I'm not sure that if they're completely accurate, So I wanted to ask somebody that has experience in this manner: Do these experiments show the right results or it's different in the real world?


texts: Is there a potentiometric method for monitoring salt formation in organic solvent?

texts:
I work in a pharmaceutical R+D lab, and currently aim to develop a validatable potentiometric method for determining the optimal amount of acid to add to a basified small organic molecule for conversion to an ionic species (i.e. sulfate salt, hydrochloride salt). Our API (active pharmaceutical ingredient) has two protonation sites, so I also need to determine the stoichiometric ratio of API to counterion, and therefore which specific salt is present at specific points of the titration curve. Ideally, this will be carried out in methanol or ethanol.

Is it possible to accomplish these goals by titrating with acid and monitoring with a conductivity meter/probe? A consultant has advised me to do so, and I have a meter with two conductivity probes. I've already tried using a pH meter, but neglected to factor in that pH is only relevant to aqueous systems. The pH method did produce decent looking titration curves with obvious inflection points. However, as major amounts of salt 'crash out' of solution, meter drift becomes an issue, the reference junction gets clogged, etc. It gets messy and I have to continually clean the probe. I've read that they make pH meters that can withstand as much as 80% organic in solution, but this is not representative of our 100% organic protocol. Furthermore, I'm having trouble finding non-aqueous calibration solutions for the pH (and conductivity) meter.

My idea: Make a set of organic conductivity calibration solutions using methanol (and/or ethanol) and neat sulfuric acid at concentrations of, say, 0.010 M, 0.10 M, and 1.0 M (arbitrarily chosen), and then carry out the titration. Ignoring solutes, this is the most representative solvent system
I can think of since I would be adding acid to methanol during the titration.

Or, am I completely going about this the wrong way? My boss and I have been researching this for over a month and have found nothing specific to the application. I suspect that I'm over complicating the matter. This type of process is surely carried out daily in drug manufacturing facilities (tons of API's are in salt form, and GMP facilities require method validation/quality assurance/etc of all analytical methods), so I assume that there is a known and developed method for this out there somewhere.


texts: Why does solid phase peptide synthesis (SPPS) always proceed from the C to the N terminus?

texts:
Is it just for historical reasons? Because the first person who did it decided to attach the C-terminus to the solid support?

Or are there chemical reasons why it would be impossible to proceed in the opposite direction?


texts:
Recently, I looked at these two papers analyzing the excited-state properties of  modified DNA bases (2-aminopurine and 8-vinyl-A) and how they are influenced by stacking with natural nucleobases:

Jean, J. M.; Hall, K. B. 2-Aminopurine fluorescence quenching and lifetimes: Role of base stacking. Proceedings of the National Academy of Sciences 2001, 98 (1), 37–41 DOI: 10.1073/pnas.98.1.37.
Kenfack, C. A.; Burger, A.; Mély, Y. Excited-State Properties and Transitions of Fluorescent 8-Vinyl Adenosine in DNA. J. Phys. Chem. B 2006, 110 (51), 26327–26336 DOI: 10.1021/jp064388h.

Briefly, the authors considered dimers comprising the respective modified base and each of the natural bases. The geometries of the individual monomers were optimized using MP2/6-31G(d,p) while maintaining their relative position within in the dimer. Afterwards, the authors examined the excited state properties with TDDFT (B3LYP/6-311+G(d)) to identify dark states that could indicate fluorescence quenching of the modified bases.

I'm not an expert in theoretical chemistry and so I was wondering how the choice of methods here was motivated. In particular, why was MP2 used for geometry optimization and not DFT? Does it have to do with a better description of dispersion interactions by MP2?

For their TDDFT calculations the authors used the 6-311+G(d) basis set. I want to try out some similar calculations using ORCA. According to the manual and online resources from the developers, Ahlrich's basis sets seem to be preferred over Pople style basis sets. Could I expect similar (or better/worse) accuracy with def2-TZVP? It's also triple-zeta and contains polarization functions on heavy atoms, but lacks the diffusion functions that were present in the studies mentioned above. Would these be important anyway in such a case were only valence transitions are investigated?


texts: What causes white board markers to dissipate when writing on dry erase painted surfaces. It almost immediately start to pull together and seems as if it disappears


texts: How to calculate the spin of atomic nuclei?

texts:
I have recently been learning about nuclear magnetic resonance spectroscopy. It is mentioned that the spin of the $^{1}$H nucleus is $\frac{1}{2}\ $and the spin of the $^{2}$H nucleus is $1$. This made me think that this likely has something to do with the number of protons and neutrons and this is indeed the case. This site  reveals that:

  If the number of neutrons and the number of protons are both even, then the nucleus has no spin.
  If the number of neutrons plus the number of protons is odd, then the nucleus has a half-integer spin (i.e. $\frac{1}{2}\ $, $\frac{3}{2}\ $, $\frac{5}{2}\ $).
  If the number of neutrons and the number of protons are both odd, then the nucleus has an integer spin (i.e. $1$, $2$, $3$).

However, I was unable to find a site which stated the exact formula needed to determine the spins of atomic nuclei. Thus, I would like to ask if such a formula exists or is the determination of nuclear spin only done through experiment?


texts: How to calculate the quantum density of states?

texts:
I've been thinking recently about Fermi's Golden Rule. Sparing the details of how to get Fermi's golden rule (you'll find like five derivations if you google it), the final result is,
$$\frac{\partial P}{\partial t}=\frac{2\pi}{\hbar}|\langle f|H'|i\rangle|^2\rho(E_f)$$which says that the probability per unit time, to first order in the perturbation from $H_1$, is a constant. Hence, this quantity tells you the transition rate. Notice, however, that it depends on the density of final states. Notice, if I'm not mistaken, that this is not for a specific state, but this is more accurately the density of all states above the original states (let's say we're in the ground state and ignore stimulated emission). I understand how to calculate the density of states for a classical, and hence continuous system. It's just an integral in phase-space.

Things become more complicated in a molecule, however, because the states are quantized. So, how do I go about doing this calculation of the density of discrete states? A really great answer would sketch out how one might do this calculation for a quantum harmonic oscillator.

I've seen a couple things online which do this kind of calculation for the motion of a particle in an infinite potential well on a solid. You basically just use the relationship between energy and the wavenumber, which is easy because you know the solutions to the Schrodinger equation for all states ahead of time.


texts: What is the molecular structure of the coating on cast iron cookware known as seasoning?

texts:
When a piece of cast iron is repeatedly covered in fat and exposed to heat it develops a hard, black, non-stick coating referred to as "seasoning".

What exactly is this coating made of molecularly? How is it bonded to the cast iron substrate? What is the chemical process that transforms a liquid fat into this coating? And what if any characteristics of the fatty acids or triglycerides used have an effect on the final coating or how well the it bonds to the iron?


texts: Failure to Locate Stationary Point in GAMESS

texts:
I'm currently trying to optimize the geometry of a complex using GAMESS at the B3LYP level. However, I keep failing to converge the SCF. I've already tried the following:

increasing the number of iterations up to 300
increasing the convergence criteria up from 0.0001 to 0.0005
Switching on DAMP
Switching DIIS on and off.
Switching off SOSCF

I'm out of ideas. What else can I do? It's interesting to note that I'm testing the ligand against 3 metals: Copper, Zinc and Iron. While Copper and Iron fail to converge, Zinc converged on my first try. Would it be fair to say that given the same ligand, the complex I've designed is "impossible"?

Thanks!


texts: How to develop a retrosynthesis plan for 2-[(E)-2-(3-bromophenyl)ethenyl]-1,3-benzoxazole?

texts:
I need to retro-synthetically design a valid synthesis plan (in two steps, from cheap starting materials available over at Sigma Aldrich) for a target compound, pictured below.

How would I go about doing this?


texts: Why does Calcium (specifically Calcium Carbonate) inhibit the Citrate buffer system?

texts: Is it because citrate chelates calcium and then is unable to react with other chemicals being added? If so can someone explain this reaction to me, or if not provide what the reason is? If anyone has any studies they've found on it that would be incredibly helpful! Thank you!


texts: Effect of charge density on electrolysis of dilute sulphuric acid

texts:
I am told that if electrolysis of dilute sulfuric acid is performed under high charge density, then the following reaction takes place at anode instead of evolving oxygen:

$$\ce{2 HSO4- -> H2S2O8 + 2 e-}$$

Why is that? And can a general conclusion be drawn?


texts: What would be the identification reactions of selenate(IV) ion?

texts: I have not been able to find any $\ce{SeO3^2-}$ identification reactions anywhere. Are there any?


texts: Photoelectric effect with 0 Kinetic Energy?

texts: Does the photoelectric effect take place if the frequency of the photon is exactly equal to the threshold frequency of the metal? I know the electron is going to be free, but it will have 0 kinetic energy; it will be stationary. If so, can voltage be still created if the metal surface is connected to a positive terminal side?


texts: Why are p-type solar cells more prone to degradation in space than the n-type ones?

texts:
Why are p-type (boron doped substrate) solar cells more prone to degradation in space than n-type (phosphorus doped substrate)?

All the sources I've looked at simply state it was found that p-type degrades slower, hence they were used for space application.

What is the main damaging radiation from the sun?
Why is it more damaging to p-type than n-type?


texts: Forming hydrogen sulfide from electrolysis of sodium thiosulfate

texts:
So I was doing electrolysis on two silver electrodes and sodium thiosulfate.
Some observations

The voltage drops extremely fast from 2 V to less than 1 V in 15 minutes, possibly because of the thiosulfate reduction.
Gases are liberated out of solution.
The solution turns black quickly.

Alert: I am using a fume hood.

Since I'm afraid of this spoiled eggs smell I just want to know if I am in any way creating hydrogen sulfide? Just want to be sure that the gas is tetrathionate and not hydrogen sulfide.

My other concern is with the voltage. How can I keep it from dropping so fast?


texts: Reference request on potassium cyanide production method

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I kindly ask for a reference for the following claim about potassium cyanide, found at potassium.atomistry.com:

  It is also obtained by the action of a mixture of steam and nitrogen on potassium carbonate.

I'd be very interested to know the temperatures required and yields obtainable, and of course if this works at all.


texts: The effect of baking soda on water electrolysis

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Ok, so now I have a new question, what type of electrode should I use. I am intending to use a simple stripped wire as my electrode, but am concerned whether the average copper wire would react and create unwanted byproducts. Is it ok if I use copper, or is some other metal better suited to this experiment.

EDIT:

I believe more baking soda would result in more gases because more free floating ions means more conductivity, which would probably allow more redox reactions to occur, and thus allow more gases to be produced.


texts: Is melting aluminium in the presence of carbon dioxide desirable?

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So aluminium cans melting is prone to formation of aluminium oxide due to presence of oxgygen and thin sheet of aluminium (large surface area). To mitigate this I can design a cruicible which is filled with $\ce{CO2}$ from bottom so it displaces air before the start of melting process as well as a check valve to eliminate fumes and built up of pressure while heating.
Question: Will this process be successful in mitigating formation of aluminium oxide? I know in argon welding, they keep purging argon on the welding area (dynamic seal) to prevent formation of oxide, but in case of aluminium, will $\ce{CO2}$ suffice? Also is there any cheaper alternative?


texts:
I have a compound named 7-(2,4-dimethyl)hexyl-3-ethyl-5,9,11-trimethyltridecane. I have a few questions:

why is it (2,4-dimethyl)hexyl and not (2,4-dimethylhexyl)? I asked this question because I saw a compound named 2,5-dimethyl-4-(2-methylpropyl)heptane, and not 2,5-dimethyl-4-(2-methyl)propylheptane.
why is the 7-(2,4-dimethyl)hexyl put before 3-ethyl? Shouldn't hexyl be put after ethyl, because e comes first than h?