texts: Nitrocellulose (flash paper) synthesis without Sulfuric Acid?

texts:
According to the Wikipedia page on Nitrocellulose:

  The process uses nitric acid to convert cellulose into cellulose nitrate and water:
  $$\ce{3HNO3 + C6H10O5 ->[H2SO4] C6H7(NO2)3O5 + 3H2O}$$
  The sulfuric acid is present as a catalyst to produce the nitronium ion, $\ce{NO2+}$. The reaction is first order and proceeds by electrophilic substitution at the C−OH centers of the cellulose.[8]

Since I have been on quarantine, I have lost access to the lab and therefore must carry out reactions from the comforts of my home. I have some sulfuric acid drain cleaner that is sufficient for many at-home applications. However, it consists of only about 93% $\ce{H2SO4}$, and contains a lot of dark dyes. I am trying to synthesize nitrocellulose paper from letter printer paper and envelopes, for the purpose of developing a self-destructing letter that burns away when the letter is returned to the envelope after being removed. However, the dyes in the sulfuric acid severely discolor the paper, and make it stand out considerably in a pile of mail, defeating the purpose of secrecy. So, at least until the quarantine is lifted, I may need an alternative catalyst to Sulfuric acid to synthesize the nitronium ions in vitro. Does anyone have an alternative to $\ce{H2SO4}$, or a way to eliminate the dyes without distillation? (because I broke my condenser column, and can't use the lab's)

Update: I'm still curious about my question, but it might not even be legal to send nitrocellulose envelopes through the mail. One spark and you could end up with flaming mail processing machines. Yikes!


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Any ideas on how to get $\ce{C3H8O3}$ (Glycerol) from $\ce{CH4}$?

My theory is that by reacting $\ce{CH4}$ with $\ce{Cl2}$ (or $\ce{Br2}$), getting $\ce{CH3Cl}$, then Wurtz's method to $\ce{CH3CH3}$, adding $\ce{Cl2}$ (or $\ce{Br2}$) again, getting $\ce{CH3CH2Cl}$, then reacting with $\ce{NaOH}$ to get $\ce{CH3CH2OH}$, and finally $\ce{CH3CH2OH + CO2 + H2O}$ and getting glycerol ($\ce{C3H8O3}$), but my way seems rather off to me so I need some help.


texts: will the autoionization of water reduce due to common ion effect?

texts:
When a weak acid is added to water , will the dissociation of water reduce due to common ion effect caused by increased H+ concentration due to acid , my text book said common ion effect is caused by a strong electrolyte
Moreover this doubt is a part of a larger doubt - if multiple weak acids are added in water will they reduce each others and water's dissociation as compared to their dissociation in their individual solutions ( due to common ion effect caused by H+ ions ) They should ? Having this doubt because the textbook I'm using just adds up their normal dissociations irrespective of common ion.


texts: Some materials emit more photoelectrons than others - why?

texts:
Again, I'm a physicist turning to chemists (so bear with me). So I've been measuring some materials by changing the wavelength of the incident light on the material and I have a detecting tip like in the diagram below:

And I might get a response that looks like this

Both materials have the same HOMO (organics) / Work Function (Metals). For example, I hardly detect any photoelectrons (emitted electrons) from stainless steel, but loads from copper (both roughly 4.5eV).

However, I am more interested in organics, why might some substances (e.g certain blends of perovskites) emit more than others (even if I have exceeded the energy required to lift an electron from the HOMO to the vacuum level)?

I thought it might be related to Density of States in metals, but this effect is also found in non-lattice molecules.

Could this be related to the related to the reversibility of the reaction (one scientist mentioned this off-the-cuff, but I never managed to catch his name to ask him to explain it further)? Essentially his idea was that molecules that can easily lose or win an electron by an outersphere process (?) (which are likely to have a clean reversible CV voltagramm) and exhibit a strong response in spectroscopy where an electron is given.

I do realise this is a bit more open ended than most questions here on Stack Overflow. But any advice or suggestions is appreciated.


texts: DFT optimization of a molecule in gaussian and find electrophilic sides

texts:
I am not a pro, but I have some experience with gaussian. For example, I can optimize a structure, calculate the frequency and rotational energies.

In the lab I made a nucleophilic substitution reaction where the Nucleophile $\ce{X}$ reacted with $\ce{R-\text{alkyl}-CH2-I}$ to form $\ce{R-\text{alkyl}-CH2-X}$ (iodide was eliminated). However, my molecule has on another position a benzylic bond "$\ce{R-Ph-CH2-O-R}$" as well and I noticed that a side reaction can occur at that position (depends on the nucleophile $\ce{X}$) where the nucleophile $\ce{X}$ reacted with "$\ce{R-Ph-CH2-O-R}$" to form "$\ce{R-Ph-X}$".

So there are two reactions: (1) The normal reaction with the alkyl $\ce{R-\text{alkyl}-CH2-I}$ to form $\ce{R-\text{alkyl}-CH2-X}$ and the side reaction (2) where the benzylic position in $\ce{R-Ph-CH2-O-R}$ is cleaved by the nucleophile $\ce{X}$ to form $\ce{R-Ph-X}$.

I am now trying to understand why the nucleophile $\ce{X}$ reacted with a benzylic $\ce{CH2}$ group at all even when its just a 15% conversion rather than the $\ce{R-\text{alkyl}-CH2-\text{Halogen}}$ group which is the favoured reaction. I think this could be illustrated by MOs, what do you think?

I already optimized the structure of my molecule and generated the formatted checkpoint file to display the molecular orbitals with GaussView. When I actually look at the HOMO and LUMO I don't get any useful information. At the benzylic position there is not really a high coefficient (no big MO) and at the $\ce{CH2}$ atom of "$\ce{R-CH2-I}$" there is even a smaller coefficient.
I had expected to see at least a big MO at the carbon atom of the alkyl $\ce{R-CH2-I}$ - where the nucleophilic reaction is favoured - but thats not the case.

So my question is, how can I analyze the reaction behaviour with DFT calculations, especially with Gaussian? I think calculating transition states is to much. It would be nice to just get some useful information about the molecules reactive sides (electrophilic sides where nucleophiles can react). How can I do that? Which calculation should I make?

By the way I used this B3LYP basis set:
b3lyp/6-31g(d,p) nosymm geom=connectivity

Thanks.


texts: In atomic diffusion in Au/Cu metal contact, where do the atoms come from ? (need melting temperature to break bonding in lattice ?)

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It is known that Au metal is diffused when it is contacted with copper metal. And Au metal have lattice which consist of atoms. If so, may I think that atom is diassociated from lattice by heating ? If so, it needs to break bond between atoms before diffuion ?
I think that it needs melting temperature to break bonding in lattice.


texts: Can sodium hypochlorite soak all the way through an unglazed ceramic cup and bleach blue paper wrapped around the outside of the cup?

texts: My question is regarding the ionic properties of sodium hypochlorite in house hold bleach. There is a debate among potters whether bleach will kill mold growing on a porous ceramic cup. It is my understanding that sodium hypochlorite cannot penetrate a porous surface of fired clay. Someone did an experiment where they put household bleach in an unglazed cup and allowed it to soak through. There was blue construction paper wrapped around the outside of the cup and the paper turned white after a while seemingly from bleaching. So my question is this: If the ionic properties of sodium hypochlorite will not allow it to penetrate through the cup to the outside, then how did the blue paper wrapped around the outside of the cup get bleached?


texts: Radicals vs atoms having unpaired electrons

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In organic chemistry course, I read that a radical is an atom, molecule or ion which have unpaired valence electrons.

So does there any difference between chlorine atom or cholrine radical? Also sodium atom contains one valence electron which is unpaired, then does sodium atom is also considered a radical?
Please clarify it.


texts: Does fumaric acid form stronger hydrogen bonds than maleic acid?

texts:
My book claims:

  Fumaric acid can form intermolecular hydrogen bonds (strong) while maleic acid forms intramolecular hydrogen bonds (weak), hence fumaric acid has higher boiling point than maleic acid."

The intermolcular hydrogen bonds in fumaric acid are said to be stronger than the intramolecular hydrogen bonds in maleic acid, while I thought that intramolecular hydrogen bonds should be stronger than intermolecular hydrogen bonds. So, which one is correct?


texts: I know that subcritical and supercritical $\ce{CO2}$ are excellent solvents. I've seen some examples of plastics being damaged by the $\ce{CO2}$ being impregnated into the plastic at very high pressures, but in general would liquid $\ce{CO2}$ be able to dissolve plastic?


texts: Rushed publications based on flawed data

texts:
In 2014 BICEP2 made a very controversial press release. It was rushed, given before any papers where published, because they feared they would be scooped by another similar experiment. In the end it turned out that their analysis of their data was flawed. It was particularly dramatic because if they had been correct it would have been a significant development.

Are there any similar cases in chemistry? Not necessary an identical situation, but a high profile result that was released in a hurry that later turned out to be incorrect.


texts: Why does the potential difference of a current drop, when silver nitrate is added to deionised water?

texts:
Semi-related to Why do some salt ions in solution conduct electricity better than others?

After conducting more experiments, using deionised water as an analyte only, I found the potential difference decreases as more silver nitrate is added. This goes against what I was lead to believe that it is actually disruption in forms of "pure" water that actually conduct electricity (i.e. pure water should not technically conduct electricity at all).

This graph shows how the potential difference drops, from my findings. The last data points plotted are at 1cm3 of silver nitrate added; the interval is 0.05cm3.

So, why is it that I see a massive drop in potential when even the slightest (0.50cm3) amount of silver nitrate is added?


texts: Does solubility of acetic acid depend on the pH?

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Does the solubility of acetic acid increase or decrease in water if I adjust the pH?

Conversely, a water-insoluble molecule (like retinol), can its solubility be increased by adjustment of the pH?

I would say no (in both cases) because the protonating or deprotonating these molecules does not change their overall hydrophilic or hydrophobic character.


texts:
Is there such a thing as a dye that can stain both oil and water?  In other words, does anyone know of an amphiphilic dye?  Maybe a surfactant that is also a pretty shade of blue?  Or maybe turn one color in oil, but another in water, but stain both well?
Thanks


texts: Is the thermodynamic stability against reduction/oxidation of an electrolyte dependent on the electrode material?

texts:
Consider an electrochemical cell with an inert Pt working electrode (WE) and some electrolyte that irreversibly decomposes upon oxidation. A minimum potential $E_{min}$ (vs. some reference) needs to be applied to the WE to allow oxidation to occur (but most likely a higher value is required to actually measure a current). I would call this potential the thermodynamic stability potential limit (SPL).

Does this minimum potential change when exchanging the WE material with another inert material, e.g. glassy carbon? I think it should not, as all that matters is the electrochemical potential/fermi level in the inert electrode.

Could some type of specific adsorption of electrolyte components change (lower) the thermodynamic SPL? To me this sounds like catalysis, which just influences kinetics, not thermodynamics.

What about adding some other substance? Could its reaction products cause degradation of the electrolyte components in some way?


texts: Ring opening of aziridinylmethyl and oxiranylmethyl radicals

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When a radical is alpha to a three-membered ring, it is common for the ring to open via β-scission (to relieve ring strain):

When the ring contains a heteroatom there are a couple of different possibilities:

Ab initio studies of these reactions1 showed that for both X = O and X = NH, the C–C cleavage was thermodynamically favoured (presumably due to stabilisation of the subsequent radical by the adjacent lone pair). For X = O, the C–C cleavage was also found to be kinetically favoured, but for X = NH, the C–N cleavage is kinetically favoured!

This regioselectivity is also backed up by experiment2 and also has potential for use in synthesis.3

Is there an explanation for why the kinetically favoured products are different for X = O and NH?

References

Pasto, D. J. Ab Initio Theoretical Studies on the Ring-Opening Modes of the Oxiranyl-, Aziridinyl-, Oxaziridinyl-, and Thiaranylmethyl Radical Systems. J. Org. Chem. 1996, 61 (1), 252–256. DOI: 10.1021/jo9505942.
Marples, B. A.; Toon, R. C. An investigation into the β-cleavage of aziridinylcarbinyl radicals. Tetrahedron Lett. 1999, 40 (26), 4873–4876. DOI: 10.1016/S0040-4039(99)00900-4.
Prévost, N.; Shipman, M. Intramolecular Radical Rearrangement Reactions of 2-Methyleneaziridines: Application to the Synthesis of Substituted Piperidines, Decahydroquinolines, and Octahydroindolizines. Org. Lett. 2001, 3 (15), 2383–2385. DOI: 10.1021/ol016194k.


texts:
I do not understand why and how an atom with $\ce{sp^2}$ hybridization has only one p orbital??

For example in pyridine why is the lone pair of nitrogen not counted as a pi electron.


texts: I think there are $\ce{C^{4-}}$ and $\ce{C^{2-}}$ existing. How can we find the charge of ions in the elements? Should we look at the group or valence?


texts:
Example from the Recommendations 2013. Left: Alleged disilazane ; Right: My version

Clearer example without obvious flaws in alternative structure. Left: Alleged disilazane ; Right: My version

I am confused with the contemporary IUPAC nomenclature of organic compounds. According to Recommendations 93 (available at acdlabs.com), silazanes are heterogeneous hydrides where both terminal atoms are silicon atoms (R-5.1.4.2). The same can be concluded from the general rule on heterogeneous hydrides (R-2.2.3.2). However, in the introductory chapter of Recommendations 2013 (which is freely available at RSC Publishing site) on page 82 the compound given in the image is given two names, with the least priority (non-PIN) variant being 1,1′-(2-ethenyl-1,2,3-trimethyldisilazane-1,3-diyl)bis(ethan-1-one). I am confused by this name, as, by rule R-2.2.3.2, terminal atoms should be lowest in the Hantzsch–Widman order, which preserves unambiguity of the structure. From this rule, I expect disilazane to be something like the structure on the second image (although I acknowledge that the tetravalent nitrogen must be positively charged, which changes the name automatically).

TL;DR So the question is:

  Do Recommendations 2013 change something about naming heterogeneous hydrides? And if so, what is now called silazanes?


texts:
Which is more conducting - molten sodium chloride or molten magnesium chloride?

I'm pretty sure I know the answer to this but my problem is putting into words. Magnesium is more conductive due to its 2+ charge, and the $\ce{NaCl}$ having a neutral charge. Right?

Would I be right in saying that as the compounds are heating up and melting the ions break away from each other and the ratio of ions in $\ce{MgCl2}$ is 2:1 so therefore the solution would be more highly charged than that of the $\ce{NaCl}$?

I know I'm on the right track, just struggling to explain it.


texts: Reduction of nitrobenzene in alkaline medium

texts:
My teacher listed out the following set of reactions under the aforementioned topic:

He explained the formation of azoxybenzene as follows.

Reduction of nitrobenzene produces 2 intermediates:

nitrosobenzene
phenylhydroxylamine

He then went on to say that condensation between nitrosobenzene and phenylhydroxylamine yields azoxybenzene. This takes place by the nucleophilic attack of the lone pair on the nitrogen atom of phenylhydroxylamine (as opposed to that of the lone pair on the oxygen atom of the same) on the nitrosyl nitrogen. He reasoned that nitrogen, being less electronegative, is more nucleophilic than oxygen (see figure). While I do understand that the explanation is generally true, I am not sure that it is the case here as the lone pair on the nitrogen atom is in conjugation with the benzene ring here and is thus less available on nitrogen. Thus, shouldn't it be the lone pair of the oxygen atom that takes part in the reaction instead?

He followed this discussion up with a question where we had to figure out the product of a similar condensation reaction in an alkaline medium between p-Nitrosotoluene and 4-Nitrophenylhydroxylamine which basically reduces to deciding which benzene ring will be directly attached to the nitro part of the azoxy moeity. He said that it is the ring with the nitro substituent that finally gets attached directly to the
nitro part of the azoxy moeity as the nitro substituent stabilises the negative charge on the oxygen of the nitro part of the azoxy moeity better (see figure).  But I can't see how that should come to be because the internal attack of the lone pair on the other nitrogen atom which establishes the N-N double bond of the azoxy moeity and removes the -OH group in the intermediate should be better available in case of the benzene ring with the methyl substituent in the first place. So, shouldn't it be the other way round?


texts: Correlating specific heat (Cp) of a substance with other substance on the basis of similar physio-chemical properties

texts:
I am modelling $\ce{H2O2}$ decomposition in ANSYS Chemkin-Pro and I have difficulty finding $C_p$ (specific heat at constant pressure) for liquid $\ce{H2O2}$ for various temperature ranges.
My ultimate aim is to find the 14 NASA polynomial coefficients so that I can input them in Chemkin-Pro. For that I need a range of $C_p$ vs $T$ data, so that I can fit the data and find the coefficients.
So I was wondering whether we can correlate specific heat of $\ce{H2O2(l)}$ with some other species on basis of same physio-chemical properties?
If yes, then I can try finding $C_p$ vs $T$ data for those other species. I know that this will cause some error but that is better than having no data at all.
I don't have a background in physical chemistry, so if anybody can help, it will be really helpful for me.


texts:
Which chemical is used in drunken driver test?

Acidified K2Cr2O7
KMnO4
Chromyl Chloride
H2O2

On searching on Google, I got the answer as option 1, acidified potassium dichromate, but my questions are:

How is the test administered? How much time does it take for the results?
On searching, I got a hunch that it had something to do with oxidation of alcohol, so, why can't we use the chemicals of the other options mentioned?
Is my hunch correct?


texts: How much CO2 gets free when combusting 6 kg n-heptane (C7H16)

texts:
I am very new to chemistry and have a question to an exercise.
It's about combustion (complete oxidation) n-heptane ($\ce{C7H16}$).

There were several questions I could answer, for example the chemical equation:
$$\ce{C7H16 + 11O2 -> 7CO2 + 8H2O}$$

But what I can't answer is, how I calculate how much $\ce{CO2}$ gets free when burning 6 kg of the n-heptane.

Can someone help me with this?
Thanks a lot!

Edit:
I am not sure if this information is needed:

molar mass (g/mol): $\ce{C}=12$ $\ce{O}=16$ $\ce{H}=1$

density of n-heptane: $0.684\ \mathrm{kg/L}$


texts:
E-liquids are blends of nicotine, propylene glycol, vegetable glycerin, and aroma.
I need to develop a method for determining the concentration of nicotine in a vial.
(to verify if the information listed on the bottle are correct.)

Does anyone have any idea how to proceed?


texts: Why doesn't a fractured salt crystal stick back together?

texts: If you crack a large crystal of a salt like NaCl, why don't the pieces spontaneously bond back together on contact? The bonding is an exothermic process and the charged ions are presumably stuck approximately right where they were before the facture.


texts: The best way to designate unsaturation (double bond)

texts: Although it has already been explained here that the use of the "Δ" (Greek capital delta) character is not recommended to designate unsaturation in individual names, IUPAC 1989 Nomenclature of steroids states that it may be used, however, in generic terms, like "Δ5-steroids"; see note 3) on page 10. What are the current trends on whether should we continue or cease using the "Δ" symbol to describe a double bond per se (rather than in the name of a steroid) or just the position of such bond between consecutively numbered junctions, in various relevant compounds, not just steroids? Isn't it a concise and elegant way to denote such a bond, or is there a better, modern, suggested, clear way? Are there recommendations or best practices documents published on that, or research papers? For, example, instead of writing "steroids with a double bond between carbon 5 and 6 junctions" we could simply write "Δ5-steroids", an example given in the note 3) on page 10 of the UIPAC Nomenclature of steroids of 1989? Here is such an example in practice, in a 2020 publication (quote): "couple of Δ5-steroids with hydroxyl group at C3 position". Can we just use the "Δ" symbol to describe the position of the double bond e.g. "3βHSD isomerizes the double bond from the Δ5 to the Δ4 position" or just (quote): "Δ5 → Δ4 isomerization by 3βHSD"? Or should we cease the use of the double-bond position as a common denominator in favor of other similarities in a group of compounds, e.g. "3-keto-steroids" instead of "Δ4-steroids" or "3-hydroxy-steroids" instead of "Δ5-steroids"?


texts: Can a molecule be achiral whilst it's resonance form chiral?

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I'm trying to work out whether methylphenylsulfoxide is a chiral molecule.

It is my understanding that the sulfur uses sp2 hybridised orbitals. Why is this? The central sulfur atom is bound to 3 atoms and then has a lone pair, so surely it has to use sp3 hybridised orbitals?

Or does it use sp2 hybrid orbitals so the empty p orbital allows for extended delocalisation of the benzene ring through the sulfur and onto the oxygen?

Apparently there are resonance forms of this molecule which are chiral.

This molecule looks odd to me, would it make more sense to have electrons resonate out of the benzene ring?


texts: Clarification of term symbol explanation of laser crystal doping from textbook

texts:
I am currently studying Diode Lasers and Photonic Integrated Circuits, second edition, by Coldren, Corzine, and Mashanovitch. In chapter 1.2 ENERGY LEVELS AND BANDS IN SOLIDS, the authors say the following:

In gas and solid-state lasers, the energy levels of the active atomic species are only perturbed slightly by the surrounding gas or solid host atoms, and they remain effectively as sharp as the original levels in the isolated atom. For example, lasers operating at the $1.06 \ \text{$\mu$m}$ wavelength transition in Nd-doped YAG, use the $^4\text{F}_{3/2}$ level of the Nd atom for the upper laser state #2 and the $^4\text{I}_{11/2}$ level for the lower laser state #1.

I don't understand what is meant in this part:

For example, lasers operating at the $1.06 \ \text{$\mu$m}$ wavelength transition in Nd-doped YAG, use the $^4\text{F}_{3/2}$ level of the Nd atom for the upper laser state #2 and the $^4\text{I}_{11/2}$ level for the lower laser state #1.

I understand that these are term symbols. However, these are usually taught in the quantum mechanics part of physical chemistry textbooks, rather than physics-focused quantum mechanics textbooks. I have only just begun slowly studying physical chemistry, so I do not yet have any exposure to term symbols. Furthermore, after skimming through the textbook, this looks like it might be the only section (or at least one of the only few sections) that use term symbols. Therefore, I do not want to get hung-up on this part, and would rather keep progressing and then learn the details of term symbols when I get to them in my physical chemistry textbook. So I was wondering if people here with physical chemistry understanding would please take the time to explain what this is saying in a way that does not require understanding of the details of term symbols, so that I may understand "the gist" of this part of the textbook and move on.


texts: Why does aluminum foil "electrocute" dental fillings?

texts:
This is probably one of the weirdest questions on here. When I was a kid, I put aluminum foil in my mouth (maybe it was still attached to some food or something, I don't remember.)

Anyway, it made my mouth feel like I'd licked a 9-volt battery. Being the natural born scientist, I repeated the procedure with similar results.

Why does this happen? I really think it has something to do with my dental fillings since the sensation occurred near them.


texts: A chemical compound with these conditions?

texts:
I am searching for a chemical compound which meets these five conditions:

slightly soluble in water
layered strutcture
ionic conductor
thermochromism
lead must be a part of it.


texts: Proportion of gases in Ideal Gas Mixture?

texts:
Suppose methane ($CH_4$) and ethane ($C_2H_6$) in a container. The specific gravity is $r_g=0.6$. I think this means $0.6=\frac{\rho_{CH_4}}{\rho_{C_2H_6}}$. Now I am trying to understand the question.

  Question: what is the proportion of gases?

Solution according to my teacher: $C_{CH_4}=0.1$ and $C_{C_2H_6}=0.9$

My Solution: $C_{CH_4}=24.2\%$ and $C_{C_2H_6}=75.8\%$

  Values (Curtis Phase Behaviour book p.162)

    $M_{CH_4}=16.04 \frac{lbm}{lbm-mol}$
    $M_{C_2H_6}=30.07 \frac{lbm}{lbm-mol}$

  What is $x_{CH_4}=\frac{n_{CH_4}}{n_{CH_4}+n_{C_2C_6}}=\frac{n_{CH_4}}{n}$?

    By Amagat's law and Dalton's law here,
    I know $\frac{n_j}{n}=\frac{P_j}{P}=\frac{V_j}{V}$.
    Specific gravity $0.6=\frac{\rho_{CH_4}}{\rho_{C_2H_6}}$ where $\rho=\frac{m}{V}$ and constant $V$ so
    $0.6=\frac{m_{CH_4}}{m_{C_2H_6}}$ so $m_{CH_4}=0.6m_{C_2H_6}$.
    $PV=nRT\rightarrow n=\frac{PV}{RT}$ where constant $\frac{V}{RT}$ so
    $x_{CH_4}=\frac{P_{CH_4}}{P_{CH_4}+P_{C_2C_6}}=\frac{P_{CH_4}}{P}=_{(1)}\frac{n_{CH_4}}{n}=\frac{V_{CH_4}}{V}$.
    By $M_i=\frac{n_i}{m_i}$ so $n_i=M_i m_i$ where $n_{CH_4}=M_{CH_4}m_{CH_4}$

  so

  $\frac{n_{CH_4}}{n}=\frac{M_{CH_4}m_{CH_4}}{M_{CH_4}m_{CH_4}+M_{C_2H_6}m_{C_2H_6}}=_{(2)}\frac{M_{CH_4}0.6m_{C_2H_6}}{M_{CH_4}0.6m_{C_2H_6}+M_{C_2H_6}m_{C_2H_6}}=\frac{0.6M_{CH_4}}{M_{CH_4}0.6+M_{C_2H_6}}=0.242455$

  $\rightarrow\frac{n_{C_2H_6}}{n}=1-\frac{n_{CH_4}}{n}=0.757545$

  where the results are not 0.1 and 0.9.


texts: In metal complex electron counting, is the neutral or ionic formalism more correct?

texts:
I have been practicing finding total valence electron counts by both methods, and a few points have arisen that have confused me.
1) Which method gives the true d-electron count?
From what I understand, the ionic method assumes that both electrons from a bond go to the more electronegative atom, and the bond is 100% ionic. This lines up with formal oxidation state which uses the same premise. As a result, d-electrons are usually calculated as completely lost from the metal, giving a positive formal oxidation state.
In the neutral method, the d-electron count doesn't change as all calculations assume that M-L bonds are cleaved such that both species are neutral, and metal oxidation state stays at 0.
This results in 2 different values for a d-electron count, and I was wondering if the value actually means anything. I guess it doesn't matter in the end as the same number of electrons are put into the overall MO scheme, but I was wondering if being asked the d-electron count has any point to it. This can be seen in the below example from here:

2) If the neutral formalism is used, where does the electron deficiency in positively charged complexes come from?
In the ionic method, we assume everything is charged and just take electrons out of the metal to account for the overall charge (even this seems strange, why do we take electrons from the metal when we could take them from anywhere else to give the same MO scheme?). But in the neutral formalism, if everything is assumed neutral, where are we supposed take the electrons from?
3) If the electrons don't have to be taken from the metal, what is the point of assigning metal oxidation state?
I always hear statements like "d8 metals such as Pt(II) commonly form square planar complexes", but both the assignment of d8 and Pt(II) differ when using a different formalism. So is the use of the ionic method and oxidation of the metal specifically simply a convention that allows us to compare complexes quickly by their total electron count?
It seems to me like the correct answer is somewhere in between the 2 methods (between 100% ionic and 100% covalent), and the use of one or the other is arbitrary, but any corrections would be appreciated.
Also, if oxidation state is arbitrary, is the argument that "metals with lower ionisation energies reach higher oxidation states so can form more bonds" the same as saying "metals that have lower ionisation energies generally have larger radii so can fit more covalent bonds around them"?


texts: Does a double bond or a triple bond have a higher priority in nomenclature?

texts:
I have this structural formula:

Should it be named pent-1-en-4-yne or pent-1-yn-4-ene?


texts: Is the given stereoisomer of 1,2-dimethylcyclobutane chiral?

texts:
I was going through some problems of chirality when I came across the following compound

  Is the given compound chiral?

My attempt

If we look at its mirror image about a mirror which is perpendicular to plane of the molecule, the two $\ce{-CH3}$ groups which is pointing upwards and downwards (implied by the wedge and the dash) will interchange their positions but then also the mirror image would be perfectly superimposable on the given compound. Hence it should be achiral but the answer key gives it to be chiral. I couldn't get it. Is this compound an exception?


texts:
The gauche structure of $\ce{H_2O2}$ is quite well known. It has the two $\ce{OH}$ groups in different planes at right angles. Why does it adopt this structure?

I can understand that it might have something to do with the repulsions between the lone pairs on the oxygens. But in that case a staggered structure would make more sense since that minimises the repulsion even further. Maybe another factor is at play here that I am missing.

EDIT: My main question in this post is why the gauche structure arises in the first place. However, the other post is mainly focussed on the variation of the dihedral angle in different phases. Although the OP asks why hydrogen peroxide adopts a gauche structure, a satisfactory answer has not been provided. (Note that the OP has accepted the provided answer. Since that does not answer my main question, I think a new question is justified in this regard)


texts: Does a timed reaction "ready indicator" paper exist?

texts:
I'm trying to see if such a thing exists in paper form that upon activation,  changes colour or "indicates" after a set configurable amount of time.

In other words a litmus or pH paper that can act as an egg timer. I'm by no means a chemist so please excuse my lack of protocol.


texts: How to write electronic configuration of p-orbitals?

texts:
For example, the electronic configuration for the element boron can be writen as:
1s2 2s2 2p1
However, it is can be written more accurately by taking the different p-orbitals into account:

The electronic configuration with the different p-orbitals starting from boron ascending in atomic number:

B - 1s2 2s2 2px1
C - 1s2 2s2 2px1 2py1
N - 1s2 2s2 2px1 2py1 2pz2
O - 1s2 2s2 2px2 2py1 2pz2
F - 1s2 2s2 2px2 2py1 2pz2

Each type of 'p-orbital' can hold a maximum of 2 electrons. But the way they are assigned to which orbital is not always systematic e.g. the electrons do no wait till, pX orbital is full to be able to fill the next one (I know this has something to do with energy levels and trends in periodic table).
Can someone tell me how this works and how I can use it to be able to write electronic configurations for p-orbitals. It is much easier just using the summation of  px + py + pz = pX; but my teacher sometimes writes it out fully...


texts: Can ferrocene type sandwich compounds be made with fluorene?

texts:
Ferrocene will be well known to made members of this site. It consists of two cyclopentadienyl anions sandwiching an iron-II ion.

During my first year organic chemistry course (about 40 years ago) I remember a friend suggesting that the fluorene anion had a similar stability and it might be possible to make ferrocene type compounds with an iron-II ion sandwiched between two fluorene anions.

A group of us persuaded a sympathetic professor to let us have a go, and as I recall we prepared the anion by adding lithium aluminium hydride to solution of fluorene in ether cooled with dry ice then adding iron-II chloride. The iron chloride immediately went into solution, so some form of complex was formed, but we couldn't get much further as on warming to room temperature we got a hideous mess of many different products and we didn't have time to analyse it thoroughly.

So my question is whether these types of fluorene compound are known, or alternatively whether it is known that they cannot be prepared? I have attempted to Google this, but there is such a vast literature on ferrocene type compounds that I have not been able to find anything relevant.


texts: Why is cis proton coupling larger than trans proton coupling in cyclopropanes?

texts:
In Clayden, Greeves, Warren Organic Chemistry Second Edition Page 815, it states:

  In four- and three-membered rings, cis couplings are larger than trans ...

but I did not find an explanation for the statement. That being said, why is it true that cis coupling is larger than trans coupling in cyclopropanes and cyclobutanes? Previously, the textbook stated that coupling is a through-bond effect, not a through-space effect, which led me to reason that the trans coupling in cyclopropane should be larger than the cis coupling, as in the case of cyclohexane.


texts: Equations for UV degradation of condensation polymers

texts:
I'm an A-level student studying the F324 unit of OCR GCE Chemistry 'A'.

The exact question is

  Explain how condensation polymers may be photodegradable. Equations needed!

I understand:

What a condensation polymer is.
Photodegradation may be possible by either a) Light-sensitive additives which catalyse a (slow) reaction in the presence of UV OR b) carbonyl bonds (C=O) breaking from the light energy.

What I don't understand:

What my teacher wants me to do for option 'a' in terms of equations. I'm inclined to leave that out, as it seems to be well outside the scope of the course.
Once the carbonyl bond breaks, what happens then? My best guess is that the oxygen atom receives the electron pair from the bond, then $H^{+}$ ions from 'somewhere' arrive to form water and finish the reaction. If I didn't know better, I'd say you needed a reducing agent for things to photodegrade.

So, what I'd ideally like is an equation (and explanation, if possible) showing what happens after the carbonyl bond breaks from UV.


texts: Hyperconjugation and the stability of alkenes

texts:
Clearly, this issue has been touched on here and here. However, I would like to raise a new point on the issue.

I have always thought that stabilisation of the $\ce {C=C}$ $\pi$ bond via hyperconjugation is through an interaction between a $\ce {C-C}$ or $\ce {C-H}$ $\sigma$ MO and the $\pi^*$ MO. This is also the explanation presented by orthocresol and Philipp in the posts linked above. However, the explanation given by Fleming (2009) is somewhat different as can be seen from the diagram below, taken from p. 74

There seems to be an internal contradiction in the text. On the previous page, Fleming does mention about the interaction between the $\sigma$ MO and the $\pi^*$ MO yet the diagram shows an interaction between a $\sigma$ MO and the $\pi$ MO. Not sure if it's a misinterpretation on my part...

On p. 73, he wrote:

  One factor is the hyperconjugative stabilisation of the $\ce {C=C}$ $\pi$ bond by the alkyl groups. Fig. 2.11 shows the interaction of the orbitals of a $\sigma$ bond with the orbitals of a $\pi$ bond, which is similar to the interaction of two $\pi$ bonds in butadiene (Fig. 1.32). Although the $\sigma$-bonding orbital and the $\pi^*$-antibonding orbital are further apart than $\psi_2$ and $\psi_3^*$ in butadiene, they are just close enough to mix in a bonding sense effectively to lower the energies of $\psi_1$ and $\psi_2$ in Fig. 2.11, making the drop in energy $\ce {E1}$ a little greater than the rise inenergy $\ce {E2}$.

Reference

Fleming, I. Molecular Orbitals and Organic Chemical Reactions. John Wiley & Sons, Ltd. United Kingdom, 2009.


texts: Why is N,N,2,6-tetramethylaniline less basic than N,N,2-trimethylaniline?

texts: According to me, N,N,2,6-tetramethylaniline should be more basic than N,N,2-trimethylaniline due to more steric inhibition to resonance, but the answer is given opposite. What is the reason for that?


texts: Phase rule for a pure substance in vapor-liquid region

texts:
I'm confused with how the Gibbs Phase Rule works for pure substances in liquid-vapor mixtures. According to the phase rule, there should only be one degree of freedom for a two-phase mixture with a pure substance. For example, if we pick a temperature for two phases to exist, there will only be one pressure that satisfies this condition. But how is the amount of vapor in the mixture, defined?
Looking at the figure below, it appears as if the pressure and specific volume are both independent of the two-phase region. Does this contradict the phase rule? If I wanted to obtain a vessel containing a mixture of water with 50% vapor and 50% liquid, could it be done by changing the pressure and temperature alone?


texts: How do I know which surfactants in hair products are aggressive to the scalp and which are not?

texts:
I'm a hair care enthusiast (I don't work with it) and a lot has been said about how bad sulfates are for hair. I say that in relation to its cleansing power. Because they are often very aggressive, such as "Sodium Laureth Sulfate" they end up removing dirt, but also all the natural oil in your hair that is healthy. It is possible to find numerous lists of surfactants that should be avoided and others that can be used (but not very reliable, since in certain lists some surfactants appear as "friendly", but in other lists they appear as "to be avoided").
Searching, I found that surfactants that have high HLB (hydrophilic-lipophilic balance) are more aggressive. Is that one criteria enough to confirm this information? If so, is there any place I can consult all the HLB for surfactants? Whether in a book or on the internet.


texts: Are the orders of reactants with respect to a reaction different for different starting concentrations?

texts:
If the reaction is repeated with $\pu{2 M}$ ethyl iodide the pyridine concentration decreases as shown below. Give the rate law of the reaction in terms of pyridine and ethyl iodide. Explain your reasoning.
$$
\begin{array}{l|rrrrr}
\hline
t/\pu{min} & 0 & 20 & 40 & 80 & 120\\
\hline
[\ce{C5H5N}]/\pu{M} & 0.1 & 0.0746 & 0.0559 & 0.0312 & 0.0175\\
\hline
\end{array}
$$

I have found the rate constant and found that the orders of ethyl iodide and pyridine are both $1$ with respect to the reaction when their initial concentrations were both $\pu{0.1 M}.$ I would have thought this would be the case for any set of initial concentrations.
I would like to confirm this. In that case, I am thinking the only thing different would be the rate constant. But how would I go about finding that?
Could I plot the data, interpret the half life and go from there? Or is my approach totally wrong?


texts: Why should space whisky taste different to Earth whisky?

texts:
I recently read an article about a vial of whisky being stored on the International Space Station for 3 years, and having its taste compared to a control sample stored on Earth.

What could cause this difference in taste / chemical composition?

Theories so far

I'd assumed that the effects of (absence of) gravity would have altered the taste by affecting how the liquid's molecules interact with one another (i.e. being free to move in space; whilst being separated into layers on Earth), though I've been told that gravity doesn't affect diffusion within a liquid.

Other possibilities that myself & my father came up with:

Effect of UV if the vial's unprotected
Effect of oxidation (due to increased surface area of the liquid in the zero-g environment, if there's any air in the vial)
Effects of increased G during take off / reentry possibly causing increased interactions between the molecules (though this would be short lived).


texts: Rate determining step for parallel reaction?

texts:
I have always read that the rate determining step is the slowest step in a reaction (source: Wikipedia).

  In chemical kinetics, the overall rate of a reaction is often approximately determined by the slowest step, known as the rate-determining step (RDS) or rate-limiting step.

However on this website (source), it says that the rate determining step for a parallel reaction is the fastest step. I was quite confused about this statement.

For a parallel reaction $\ce{B <- A -> C}$, where $\ce{A -> B}$ has rate constant $k_1$ and $\ce{A -> C}$ has rate constant $k_2$, the equations (from solving the first-order linear differential equations for A, B, and C, give: $A = A_oe^{-(k_1+k_2)t}$,  $B = \frac{k_1*A_o}{k_1+k_2}*(1-e^{-(k_1+k_2)*t})$, and $C = \frac{k_2*A_o}{k_1+k_2}*(1-e^{-(k_1+k_2)*t})$.

But I do not know how to proceed from there.


texts: How do I turn room temperature water into boiling water for drinking using an chemical/additive?

texts:
I am trying to create instant boiling water using a chemical of sorts, so that it can be consumed by a human. For example; someone could make tea without a kettle or any available water heating systems.

It must be completely safe and if possible, leave no bad tasting remains. Preferably, the chemicals used would have to be easily accessible and stable in its bought state.

I am in high school and just want to do a cool science experiment. I guess this could have endless potential applications. I am also open to other ideas, like making a disposable bottle, that when you twisted the lid, the water would heat up as the chemicals dropped down or the bottle itself heated up. Just any way of doing it would be awesome.

I saw this page but is wasn't consumable ideas:

Can you heat water with additives?

Thanks,
Charles


texts: Proposed mechanism for the catalyzed oxidation of CO by O3: Are NO and NO2 catalysts or intermediates?

texts:
The steps below represent a proposed mechanism for the catalyzed oxidation of $\ce{CO}$ by $\ce{O3}$:

  $$\begin{align}
&\text{Step 1: } & \ce{NO2(g) + CO(g) &-> NO(g) + CO2(g)} \\
&\text{Step 2: } & \ce{NO(g) + O3(g) &-> NO2(g) + O2(g)} \\
\end{align}$$

  Which of the following statements is true based on this mechanism?

  The overall products are $\ce{NO2}$ and $\ce{O2}$.
  The overall products are $\ce{NO}$ and $\ce{CO2}$.
  The overall products are $\ce{NO}$ and $\ce{O2}$.
  Either $\ce{NO2}$ or $\ce{NO}$ can be viewed as a catalyst. (correct answer)
  Both $\ce{NO2}$ and $\ce{NO}$ are intermediates.

Based on the given proposed mechanism for the catalyzed oxidation of $\ce{CO}$ by $\ce{O3}$, the answer for above question suggests that either $\ce{NO}$ or $\ce{NO2}$ can be considered as a catalyst.

Thus, I'm very confused as to why the answer is 4. I would think it is 5) because $\ce{NO}$  is produced first and than consumed later on. I understand $\ce{NO2}$  does not have that same pattern, however I thought that it cannot be a catalyst because $\ce{O3}$  is already a catalyst.


texts: Palladium is the "go to" heterogeneous catalyst for dehalogenating aryl chlorides using hydrogen. What are the chemical (not economic) reasons for other precious metal catalysts not being as common or as efficient in this reaction e.g. rhodium?


texts: if a balloon full of warm air was placed in a refrigerator, what is the result?

texts: If a balloon full of warm air was placed in a refrigerator, What will happen to the Ballon ?


texts: Does halogenation by phosphorus tribromide lead to an inverted product?

texts:
I think it follows the SNi mechanism and would not lead to Walden inversion.
Hence, the product should be (S)‐2‐bromobutane:

But the answer says otherwise (the problem didn't indicate the presence of pyridine in the reaction mixture though).


texts:
Why is a burn to the skin caused by steam more serious than a burn caused by the same amount of boiling water at the same temperature?

The temperature is the same, which implies that the kinetic energy of the particles in both the steam and the boiling water are the same; and yet the steam is more dangerous. Why so?


texts: IUPAC nomenclature of protonated aminoacids

texts:
What is the IUPAC systematic name for the above compound.

So I know that carboxylic acids have highest priority. Now the length of carbon chain is 7. So I think the name should be 7-ammonioheptanoic acid. Am I correct?


texts:
I am aware that esters can be selectively hydrolysed depending on the type of alkyl group present e.g. Me ester vs t-butyl ester, the latter is reactive to acidic conditions and not basic because of its inability to form tetrahedral intermediate. But what reagent could I use to carry out the following transformation?

I see it is the O-C bond that breaks, so it is acyl cleavage (Ac). Acidic conditions would destroy my Me ester as would basic, so how can I get around this? Could a big bulky base, say LDA, take it down a B(Ac)2 route (generate CO2?)


texts:
I don't understand why enthalpy change won't change at an equilibrium?

The reason I ask this is because of this question:

At first I thought the answer is C, but I realised that the amount depends on where the position of equilibrium lies. The correct answer is D, but doesn't enthalpy change (delta H) also depend on where the position of equilibrium lies?


texts: What exactly is Indium's ability to stabilize non-ferrous metals?

texts:
I was reading the History section about Indium on Wikipedia when I came across the following sentence:

  In 1924, indium was found to have a valued ability to stabilize non-ferrous metals, which was the first significant use for the element.

I'm wondering if the ability is to improve crystallinity, structural stability of alloys, resistance to corrosion, or something else.


texts: Which component in my tap water "scale" does not react with acid?

texts:
Where I live we have pretty hard tap water and so I'm used to scale build-up in kettles and on bathroom tiles, easily removed with acids (it's mostly calcium carbonate I guess). However it seems a part of the "scale" is resistant to acid. For example, I have a glass that I use in my office to drink tap water throughout the day, so the remaining drops of water dry often at the bottom. This results in a circle of "scale", but a significant part of that remains even after treatment with sulfamic acid. Similarly, it seems a part of the residue that forms on my bathroom tiles is not removed by acidic cleaners.

Looking at the water quality charts of my utility, the only part that I think could be responsible just by guessing at the amounts present is $\ce{SiO2}$, at 29 mg/l. Does this form a white, scale-like substance that's hard to remove, at least with acid?
(Tap water analysis here, fold down the Wasserwerk Schulensee part.)

Below an image of my glass after treatment with warm sulfamic acid. The limescale present bubbles off. The remaining white stuff can be scratched off with a knife, so it's actually a residue and not just "etched" glass, but it is pretty tough.


texts: Removal of nickel plating on MgB2 without damaging the boride?

texts: I need to remove a nickel plating of a MgB2 wire without causing damage to the MgB2. I felt that electrolysis is the best method but I do not know what electrolyte to use for this. I also need to coat it with a thin layer of copper and would like to know how I can do this without oxidation to the filament.


texts: Does rate of auto-ionization of water change after adding a strong acid?

texts:
We know that a reaction could have different rates at equilibrium. For example, lets take the reaction:
$$\ce{A + B -> C }$$
At equilibrium, the rates of formation and dissociation will be equal:
$$k_\mathrm{r}\mathrm{[A][B]} = k_\mathrm{c}\mathrm{[C]}$$
But that means at various concentrations of $\mathrm{[A],[B]}$ and $\mathrm{[C]}$, the actual velocity (rate)  of the reaction at equilibrium will be different.
In other words, for the above example: If I were to put additional [A] into the reaction after its reached equilibrium once, the new equilibrium it would reach would have a faster rate. Also, this means that a fold change increase in $\mathrm{[A]}$ doesn't require an equivalent fold change decrease in $\mathrm{[B]}$ to reach the new equilibrium.
Now, the autoionization of water is unique because it is independent of the concentration of water: $$K_\mathrm{w} = \ce{[H+][OH-]}$$
This means that a fold change increase in $\ce{[H+]}$  requires an equivalent fold change decrease in $\ce{[OH-]}$
Thus, I am guessing the rate would be equivalent to some constant: $$k_\mathrm{r}\ce{[H+][OH-]} = constant$$
Does the rate of auto-ionization of water change when you add a strong acid or base? An explanation at the level of molecules would be appreciated.


texts: Detecting alkaloids - Dragendorff's reagent

texts:
I am writing a book and as part of the plot one of the characters has a plant that contains alkaloids in tincture form. They want to do a test to detect for the alkaloids so they use the Dragendorff's reagent test. Quote below:

  Bindweed contains alkaloids. The Dragendorff's reagent is a simple test to detect for them. They had all I needed in the chemistry lab... bismuth nitrate, hydrochloric acid, potassium iodide. When I added milk to the solution it turned orange confirming the presence of alkaloids. I did a control test too and nothing happened.

Would this technically work?


texts: What does borax do in and to the washing machine?

texts:
Does borax actually do anything to make clothes cleaner? If it does ....
Does it do something with the detergent to remove more dirt from clothes?
Does it make it easier to rinse detergent and dirt out of the clothes?
Does it work only if the wash cycle uses hot water?
Does it un-dissolve in the cooler rinse cycle water and end up building up in the machine?


texts: How to find the mass of dissolved AgCl when placed in a solution of NaCl?

texts:
I think the following problem in my textbook is malformed:

  Solid $\ce{AgCl}$ is placed in $1\,\mathrm{L}$ of $0.55\,\mathrm{M}$ $\ce{NaCl}$. Find the mass of $\ce{AgCl}$ which dissolves.

I know the method to solve the problem. I think the problem is malformed: When we get an answer, say $x$ grams $\ce{AgCl}$ dissolves, but if we placed less than $x$ grams solid $\ce{AgCl}$ in the solution initially, then it would be impossible for $x$ grams to dissolve.
So we obviously have to make certain assumptions, but I am looking at the solution in my textbook and I don't see in which part of the solution is the assumption used (implicitly). And by the way, how do we solve the problem if we have place less than $x$ grams solid $\ce{AgCl}$?


texts:
In a solution, we have ions floating around but when we have a precipitate, they're arranged as they would be in a solid. This conversion should cause a decrement in the entropy of the system and cause the reaction to be non-spontaneous, but that is not the case. Data of several $K_\mathrm{sp}$'s suggests that the reactions are very spontaneous, with $\log{K_\mathrm{eq}}$ around $30-40$ for some salts. Why does this happen?

One possible explanation I could think of was that all precipitation processes are enthalpy driven instead of entropy driven but in those cases enthalpy should either be really high and all solubilities must increase upon increase in temperature. I haven't studied these enough to know if that is the case or not, so help from someone more experienced would be appreciated.


texts: Accuracy of FP-LAPW vs Plane Wave Pseudopotential: examples

texts: I am trying to learn about FP-LAPW software. I would like to know how well FP-LAPW outperforms Pseudopotential PW calculations. What are some properties/calculations/quantities in which FP-LAPW gives consistently better results than Pseudopotential PW theory? I know that FP-LAPW should give better results on almost everything (after all, it is an all-electron calculation). I am specifically looking for calculations where FP-LAPW gives much better results than Pseudopotential PW.


texts: The intrinsic electron-withdrawing nature of alkyl groups

texts:
What you are about to read may be a very mind-boggling paragraph but please do not regard it as nonsense. Please think through it thoroughly.

In Chapter 6 of Organic Chemistry (4th ed.) by Maitland Jones Jr. and Steven A. Fleming, the following is written (p. 237):

  In 1970, Professor John Brauman (b. 1937) and his co-workers at Stanford university showed that in the gas phase the opposite acidity order obtained. The intrinsic acidity of the four alcohols of Table 6.6 is exactly opposite to that found in solution. The acidity order measured in solution reflects a powerful effect of the solvent, not the natural acidities of the alcohols themselves. Organic ions are almost all unstable species, and the formation of the alkoxide anions depends critically on how easy it is to stabilize them through interaction with solvent molecules, a process called solvation. tert-Butyl alcohol is a weaker acid in solution than methyl alcohol because the large tert-butyl alkoxide ion is difficult to solvate. The more alkyl groups, the more difficult it is for the stabilizing solvent molecules to approach (Fig. 6.22). Of course, in the gas phase where solvation is impossible, the natural acidity order is observed.

Let me provide some context. The author is discussing the acidity of alcohols in the gas phase and in the aqueous phase. In Table 6.6 as shown above, the pKa values are provided to show the decreasing acidity of the alcohols as the alkyl portion increases in size. The author explains this by saying that it is not really due to the electron-donating effect of the alkyl groups, concentrating the negative charge on the oxygen atom. Rather, he argues that it is due to the decreased extent of solvation due to the steric hindrance provided by the bulkiness of the alkyl groups. This is a reasonable rationalisation.

However, the authors then go on to discuss the acidity of the alcohols in the gas phase and mention that the acidity trend is reversed in this situation. The alkyl groups now increase the acidity of the alcohol, rather than decrease it. The authors then state that it is due to the electron-withdrawing nature of the alkyl substituents. They even provide a qualitative molecular orbital picture of this "electron-withdrawing" interaction, as shown in the following paragraph (p. 238):

  Alkyl groups have both filled and empty molecular orbitals (see the problems at the end of Chapter 1 for several examples). A pair of electrons adjacent to an alkyl group can be stabilized through overlap with the LUMO of the alkyl group. (Similarly, an alkyl group stabilizes an adjacent empty orbital through overlap with the alkyl HOMO.)

I would like to ask if anyone has ever heard of such an unconventional rationalisation and whether there is a sound theoretical basis for the postulations made above by the authors. If the postulations are indeed inconsistent with current chemical understanding, please provide a clear response detailing the areas of conflict.


texts: Would you be able to identify the stretch and bend in the spectrum? I can not find much information about the $\ce{N2O}$.It's solved, does anyone know the symmetry of these vibrations?


texts: What are the bond angles in cyclohexane?

texts:
In the chair conformation of cyclohexane, what are the angles of the triangles defined by:

a carbon atom, an axial hydrogen bonded to it, and the midpoint of a vicinal C-C bond ?
a carbon atom, an equatorial hydrogen bonded to it, and the midpoint of a vicinal C-C bond ?

I have unsuccessfully looked for literature values of these, and my trigonometry is not up to scratch.


texts: Is a carbon chiral it two of its groups are cis - trans isomers?

texts:
For example:

In this image, the two groups sticking to a carbon are cis-trans isomers. So does that make the carbon chiral, exhibiting optical properties?

What if the two groups were both having the same configuration(both cis or both trans), would it then be achiral?

Thanks for any help :D


texts:
What is the reason why oxalic acid has its second $\ce{-COOH}$ group flipped?

I'm guessing it's something to do with steric repulsions between the $\ce{-COOH}$ groups but I'm not sure.


texts: If I have a chiral substrate, should I always assume that both enantiomers are present?

texts: Considering the Sn1 reaction of (S)-2,3-dimethyl-3-pentanol, knowing that this molecule has a chiral carbon, should I always assume that both enantiomers are present, and therefore the products of a reaction will always have $2^n$ products for $n$ stereocenters on the substrate, assuming that each stereocenter has equal chance of reacting? Is there two products of this Sn1 reaction due to the fact that the molecule is chiral, and therefore its enantiomer is present and has equal chance of reacting?


texts: Correlating the decrease in orbital radius and penetrating power with the increase in l value

texts:
I have read that s-orbitals have a stronger penetration effect as compared to p-orbitals and p-orbitals have a stronger penetration effect as compared to d-orbitals, etc.

Therefore, the electrons in an s-orbital are closer to the nucleus of the atom and their ionisation energies are greater than for an electron in a p-orbital. (Example: This is what we use to explain why the energy of ionisation decreases from $\ce{Be}$ to $\ce{B}$).

Everything made perfect sense to me until I read:

  The orbital radius slightly decreases with an increase of $l$ value.

Since s-orbitals penetrate more, shouldn't that mean that being closer to the nucleus, they have smaller radius as compared to an orbital with higher $l$ value, say, the p-orbital?

How can we justify this? Or are these two pieces of information not related in this way?


texts: Is it possible for one specific atom in a molecule to have a non-integer oxidation state?

texts:
I am wondering if fractional oxidation states of an atom are possible. I'm not referring to cases such as $\ce{Fe3O4}$ or $\ce{Mn3O4}$ where the average oxidation state is fractional, since these actually comprise a mixture of atoms which are individually in the +2 and +3 oxidation states. What I mean is, is it possible for an individual atom in some compound to have an oxidation state of (for example) 2.5?

To me it doesn't seem possible just because of the way oxidation states are defined. However I have seen some sources which state that fractional oxidation states are possible. I would be interested in knowing if there is some weird compound that has fractional oxidation states?

Note: This is not a duplicate of Are fractional oxidation states possible? I want to know if it is possible for an individual atom in some compound to have a fractional oxidation state, not its average fractional oxidation states.


texts: N-alkylation of amides with alkyl halides?

texts: Can amides be N-alkylated with alkyl halides? Say I was trying to make N-propyl acetamide. Would iodopropane and acetamide react to form it? Would they react to form N,N-dipropyl acetamide? If so, what catalysts would I need, and if not, why not and how would it be possible?


texts: Steric inhibition of resonance vs. hydrogen bonding

texts:
I have to compare the acidic strength of these compounds:

Now, in A and B hydrogen bonding will be present which will help stabilize the negative charge of the conjugate base. However, the hydroxyl group is not bulky and won't cause steric inhibition of resonance, hence the +M effect of phenyl will still be present.

In C, methyl will cause steric inhibition of resonance and hence stop/reduce the +M effect of phenyl which will stabilize the conjugate base.

How do I compare the relative stabilization offered by these two effects (H-bonding and SIR)?


texts: Which one is the correct molecule of the given properties of IR Spectroscopy?

texts:
$\ce{CH3CH=CHCO2CH3}$
$\ce{CH3COOCH=CHCH3}$

$\pu{2950 cm-1}, \ \pu{2870 cm-1}, \ \pu{1740 cm-1}$ are the observed peaks.

No peaks observed $\pu{1700-1500 cm-1}$.

The formula of the molecule is $\ce{C5H8O2}$.

My pre-answer is the first option. Because $\pu{1500-1700 cm-1}$ includes unsaturated carbons.


texts: It has been saying that if adding too much indicator in solution, the ph value of solution would be changed. From this, it can be saying that indicators have a pH value. Methyl orange is the indicator I used in the experiment. "My question is whether methyl orange is basic or acidic so that it affects the pH value of solutions."


texts: Why is phenolphthalein at pH 10 non-planar?

texts:
Phenolphthalein is colorless when pH = 0-8.2 and pink when pH = 8.2-12.

Why does the ring bearing the carboxylate (COO-) group not lying on the same plane as the other 2 rings?

Image source: https://www.learner.org/courses/chemistry/images/lrg_img/Pink.jpg


texts:
Cobalt exhibits a more specific interaction with histidine tags, resulting in less nonspecific interaction than nickel. For this reason, cobalt is the preferred divalent cation for purifying His-tagged proteins when high purity is a primary concern.

I read this last week, and I'm wondering, why is cobalt like that? What about it causes that?

(Source of quote: https://www.lifetechnologies.com/us/en/home/life-science/protein-biology/protein-biology-learning-center/protein-biology-resource-library/pierce-protein-methods/his-tagged-proteins-production-purification.html)


texts: How do/did chemists observer/infer the structure of organic molecules and reactions?

texts:
As I understand organic chemistry there is no simple generalization that allows us to predict reaction outcomes- rather we transform molecules using a sequence of known reactions.

This has me wondering how these known reactions came to be known. My first guess would be that the structure was empirically observed before and after the reaction.  If this is the case what instrumentation would be used to observe this?

If not, how else were these reactions determined and if they were not all developed by trial and error, what is the name of the branch of chemistry that deals with hypothesizing them?


texts: Is a time domain spectrum obtainable from a frequency domain spectrum?

texts:
I know for a fact that a frequency domain spectrum can be obtained from a time domain spectrum using a Fourier transform  - but can you do the reverse?

Also what are the advantages and disadvantages of the frequency and time domain spectra?


texts: Are there any chemical pathways or catalysts that could produce electricity from fossil fuels without combustion?

texts:
While fossil fuels are dense in energy, I have known only one way to retrieve energy from them, namely, to burn them. I wish we could have a way to get energy from them without combustion.

Is there any way we could get energy from oil, gas, diesel or other fossil fuels without burning them? Ideally, so we could making something like a battery out of them.


texts: How to determine charge of compounds in solution with many amphoteric functional groups?

texts: I am curating a metabolic model that has compounds such as NADH/NADPH/Etc. that have multiple ionize-able hydrogens. Normally with amino acids there are only a few hydrogen with varying pKas that makes it easy to find what the charge the of the molecule is and the formula at a given pH. However with NAD, I can't get a good idea of what the actual formula is at pH 7ish. I have been using Kegg, ModelSEED, pubChem, etc. There is alot of conflicting information. What is the charge/formula of NAD in particular and more important, what resources are best to determine molecular compound charges at various pHs.


texts: why does silver chloride darken when exposed to electromagnetic radiation

texts: All I know about this is that it does but I have no idea as to why and when I ask the only answer I get is "Because it does" which isn't helpful in the least. If I could get a good, well-said response, that would be great.


texts: Can I use litmus paper to test unknown liquid that contains a concentrated strong acid?

texts: Can I use litmus paper to test unknown liquid that contains a concentrated strong acid (example $\ce{H2SO4}$)? Can concentrated strong acid destroy litmus paper?


texts: Imagine a container of fixed volume is taken and hydrogen gas is filled in it, as a result the container floats in air. But if in the same container is filled with so much hydrogen that the hydrogen gas molecules had to compress to fit in the container, will the container still float in air ?


texts: Relative strengths of methyl, primary, secondary, and tertiary C–H bonds

texts:
Which of the highlighted C–H bonds in the following compounds is weakest? (R = generic alkyl group)

I personally thought that the answer was 1 but it is given as 4 in the answer key. I didn't understand how it is so.


texts: What's the solid product of the reaction of liquid ammonia with excess sulfur?

texts:
What would happen when you mix liquid $\ce{NH3}$ and excess of sulphur?

The answer key states that a solid with $\ce{N}$ and $\ce{S}$, and a gas which gives a black precipitate with lead acetate is evolved.

Surely, $\ce{H2S}$ gas will evolve. What about the solid? Is it ammonium sulphide or ammonium sulphite?


texts: Equations for reactions dealing with coordination compounds

texts:
Write a balanced chemical equation for the reaction depicted in this figure. Express your answer as a chemical equation. Identify all the phases in your answer.

This is what I have tried so far:

NH4NCS(aq) + [Fe(H2O)6]3+(aq) -> [Fe(H2O)5NCS]2+(aq) + H+(aq) + NH4OH(aq)

NH4NCS(aq) + [Fe(H2O)6]3+(aq) -> [Fe(H2O)5NCS]2+(aq) + H2O(l) + NH4+(aq)


texts: Polyurethane epoxy resin chemistry advice please?

texts:
My friend can buy polyurethane epoxy from his workplace for 3 dollars a litre, except that he doesn't know precisely the data sheet for it. His factory gets it in 20 ton deliveries.

He says that the mix has to be around 99% Polyurethane, 0.2% cobalt, and 0.8% of a toxic transparent catalyst liquid.

It's a generic industrial chemistry used everywhere, and can be mixed roughly by eye to achieve different drying speeds.

Do you know what the name of this resin system is called and where i can find precise information on it? What is the catalyst?


texts: Intrinsic Reaction Coordinate - Converting To Reaction Coordinate with Units of Distance

texts: I've located a transition state and ran two IRC calculations (one to get to the product and one to get to the reactant). Is there some type of way of approximating the IRC to something that has units of distance (Angstroms, Bohr, etc.)?


texts: What program could I use to create a protein model from scratch?

texts: I would like to create protein models such as the ones in the Protein Data Bank. I have got GROMACS but I don't know if it can be used to model macromolecules.


texts:
I am learning about how to calculate s-orbital character. While doing so, I came across a formula
$$\cos\theta = \frac{s}{s-1}.$$
For cycloproprane, I used $\theta = 60^\circ,$ and got $s = -1.$

How can the s-orbital character be negative?
What does the negative sign mean?

Question which I want to solve
Find out the stability of the following carbanion:

I found Does negative sign of s-orbital exist?, but failed to understand it. If that answers my questions, please tell.


texts: 1,4-diphenyl-1,3-butadiene (E,E) and (E,Z) Isomer Newman Projections

texts: I was wondering if it is possible to draw the Newman projections of the (E,E) and (E,Z) isomers of 1,4-diphenyl-1,3-butadiene in the following manner that I have? I wasn't quite sure about how to present the rings in such projections.


texts: Why do gummy bears explode when added to hot potassium chlorate?

texts:
This link shows that a gummy bear explodes when in contact with heated potassium chlorate, $\ce{KClO3}$. But what in a gummy bear creates this reaction?

Also, do other foods (fruit, icing sugar...) react as violently with potassium chlorate?


texts: Calculating equilibrium constant given Ka value?

texts:
$\ce{NH_3(aq) + H_3O^+(aq)  <-> NH_4^+(aq) + H_2O(l)}$
$\ce{K_a}$ for $\ce{NH_4^+}$ is $5.6\times10^{-10}$.

I am completely lost and I have no idea how to approach this question.


texts: What is the relation between Rate of reaction and rate of consumption of reactants?

texts:
The rate of the following reaction is 0.300M/s. What is the relative rate of change of each species in the reaction?$$\ce{A + 3B -> 2C}$$

We are supposed to find A and B and I understand that we have to use $\frac{ [\delta]A}{[\delta]t}$ and then use a negative for the coefficient. But what I don't understand is, why for B we had to multiply -3 but not -1/3? And is it the same for A?
Also, I am confused on how I can differentiate between using these two equations of rates. The Delta of reactants/delta of time, versus the rate $v(nu)=k[A]m[B]n$
equation.


texts: What's the mechanism for this isotopic substitution reaction?

texts:
I'm curious to know what's the mechanism of:
$$\ce{HF + D^+ \rightarrow DF + H^+}$$


texts: Can water volume reduce with introduction of another chemical

texts: Can a chemical be introduced to a volume of water which can actually reduce the volume of water in that container?


texts: Nucleophilic substitution with chloroethane: hydrogen cyanide vs. potassium cyanide

texts:
Chloroethane can be used to make sodium propanoate.
$$\ce{chloroethane -> Q -> sodium propanoate}$$
The Intermediate, $\ce{Q}$, is hydrolysed with boiling aqueous sodium hydroxide, to give sodium propanoate.
Which reagent would produce the Intermediate, $\ce{Q}$, from chloroethane?
A concentrated ammonia solution
B dilute sulfuric acid
C hydrogen cyanide
D potassium cyanide

What is the difference between using hydrogen cyanide or potassium cyanide? Why would the answer be D?


texts: Why does silver stick to the glass in Tollens' test?

texts:
Why does it not simply form a solid powder at the bottom of the flask?

Does silver also stick to the glass in other silver precipitating reactions?

EDIT:
My question is definitely not the same as the one linked (which btw does not have an answer and is inactive for three and a half years).

Normal precipitation of silver from silver ions results in a black powder and no mirror.

As pointed in the comments, kinetics seems to play a major role here, with slow precipitation being key to achieve a mirror.

So why is it that a slow reduction of silver ions make them deposit on the surface of the glass?


texts: What compounds give two products on reacting with NH2OH?

texts: This is a question from the chapter stereochemistry of my coaching module. The answer options include CH3CHO, DCHO, etc. How do I do this? I have an idea that if we take a racemic mixture of D and L isomers it is possible to get such products. Am I right? And is it possible? How do I do this question?


texts:
I'm going to be aliquoting out ethanol-stabilized chloroform into smaller containers. It's presently in a large bottle sealed with a rubber(y) sheet so I can only draw it out with a needle.

My questions are:

How do I seal them?
If I'm aliquoting to minimize exposure of the full bottle to air, can I get rid of the rubber sheet?
Are there any restrictions on the sort of cap I can use on the aliquot bottle?


texts: How do molecules know how to behave when a disturbance occurs in an equilibrium?

texts:
I am well aware of Le Chatelier's principle, but what causes molecules to behave in such a way, my guess is that it all has to do with rates of reactions and frequency of collisions.

When at a constant volume, the addition of an inert gas causes no change in the equilibrium, since the concentration of each species will remain constant, I understand that there will be the same amount of molecules per unit volume as before the addition, however wouldn't the rate or probability of collision increase since now each unit of volume has less space in which the molecules can move about due to the addition of the inert gas in that unit of volume, hence if a reaction had more moles in the forward then the reverse the probability of the forward occurring would be greater, causing a forward shift?


texts: The density of nitrogen is greater than the density of oxygen, hence the denser nitrogen would be present in the lower atmosphere. If so it would be deprived of oxygen as it would be pushed to the higher atmosphere due to its low density. But we live due to the intake of oxygen from the lower atmosphere. How is this possible?


texts: Between ethene and propene which is more acidic and why?

texts:
Between ethene and propene, which is more acidic and why? If they are they are the same then why so?
 Their $\mathrm{p}K_{\mathrm{a}}$ is the same $\mathrm{p}K_{\mathrm{a}}$ as ~44.


texts: Why is work and heat energy always viewed from the perspective of the system?

texts:
So my answer was 3 and it was wrong, And i really would like to know what is the correct answer, after giving it some thought, I think the answer is 4 because indeed it is easier to control the system than surroundings, can you please assure it that it's D.
I appreciate any help


texts: This is a weird question but it's finals week and it's impossible to get in contact with my prof. I have no idea what he means by the last line where he says a C-O bond is formed for every C-C and C-H bond. Can someone just clarify this for me?


texts: Do (simple, inorganic) salts ionize completely in water when they dissolve?

texts:
Specifically: Suppose I add equal parts (i.e. the same number of moles of each) sodium bicarbonate and potassium sulfate into a container of distilled water large enough to dissolve them completely. In a second container of water, I add potassium bicarbonate and sodium sulfate. Are these two containers now physically identical? (That is, is there any experiment that could tell them apart?) My understanding is that each now contains free-floating Na+, K+, S-, and HCO3- ions. And if I evaporate away all the water, what will be left behind in each container?

If I replace the potassium and/or sodium with, say, magnesium or calcium, and the bicarbonate and/or sulfate with chloride or citrate, do the same principles hold? (Assuming the resulting salts are water-soluble - some, like calcium carbonate, won't be.)

(I'm not sure if the list of cations and anions above have much in common chemically. My interest relates to the fact that they can be added to water to simulate the chemical makeup and flavor of natural mineral spring water.)

(PS: What's a more elegant way to say "the same number of moles of each?" If I say to mix things in equal parts, or in some ratio, I would normally specify whether I mean by mass, by volume or... how do I say "by number of moles?")


texts: What role does H2O2 have in copper (II) acetate formation?

texts:
Mixing solid copper, 5% vinegar, and hydrogen peroxide ($\ce{H2O2}$) causes copper acetate to form. The process will occur very slowly without hydrogen peroxide. Adding $\ce{H2O2}$ speeds the formation of copper acetate.

How does Hydrogen Peroxide promote the formation of Copper (II) Acetate?


texts: Why does water evaporate spontaneously at room temperature despite ΔG > 0?

texts:
Standard Gibbs free energy of formation of liquid water at $\pu{298 K}$ is $\pu{−237.17 kJ mol-1}$ and that of water vapour is $\pu{−228.57 kJ mol-1}$ therefore,

$$\ce{H2O (l) -> H2O (g)}\qquad\Delta G =\pu{8.43{kJ mol-1}}$$

Since $\Delta G>0$, it should not be a spontaneous process but from common observation, water does turn into vapour from liquid over time without any apparent interference. Why does this happen?


texts: Confused about strong/weak dibasic and tribasic acids

texts:
I know that sulfuric acid is considered a strong acid, and the dissociation of its first $\ce{H+}$ ion is complete and of its second $\ce{H+}$ ion is partial.

Phosphoric acid is weak and all three of its $\ce{H+}$ ions dissociate partially.

I just wanted to clarify: are dibasic and tribasic acids considered strong if their first dissociation is complete (and subsequent ones will naturally be partial)?


texts: Thermal decomposition of mercury thiocyanate

texts:
A video on YouTube shows the thermal decomposition of mercury thiocyanate. A strange thing I've observed is that $\ce{Hg(SCN)2}$, which is the reactant, is a white powder and the product is a yellow-brown solid serpent-like structure. How is this possible? What is the chemical reaction for this decomposition?

video link - https://www.youtube.com/watch?v=FaC4MqxUnFw


texts: Are there any other reagents except HNO3 and H2SO4 for Nitration?

texts: Is nitration of benzene possible by using any other reagents except using HNO3 and H2SO4?


texts: why does FeCl₃ have such a specific smell?

texts:
When I use $\ce{FeCl3}$ solution for etching circuits it gives off an acidic smell.
I was wondering what is the cause of the smell.
I don't think it's caused by the $\ce{Cl2}$ from $\ce{2FeCl3->2FeCl2 + Cl2}$ because chlorine has a different smell.

The product used is the one in this picture.


texts:
If you look at the concentration verses time graph of typical reactions, you can see that the concentration of reactants and products, when time goes towards infinity, becomes the equilibrium concentration. But! It never seems to reach that concentration (it converges towards that , but never reaches it). Which means that there is no 'real equilibrium??

I think this is true in terms of theory, where the number of molecules is considered to be infinite, while in reality, the number of molecule is finite. Then, in reality, it reaches equilibrium??


texts: How do you determine which entity gains or loses an H+ in an equation?

texts:
$$\ce{HCO3- (aq) + H2O(l) <=> H2CO3(aq) +OH- (aq)}$$

I do not understand why this makes an Arrhenius base and why it doesn't form:
$$\ce{HCO3- (aq) + H2O(l) <=> CO3^2- (aq) +H3O+ (aq)}$$

Could someone explain this to me?


texts: Suggest a method, other than spectrophotometry, for determining the reaction rate

texts:
For the hydrolysis of $\ce{\mathit{trans\hyphen}[Co(en)2Cl2]Cl}$ (and cis) we measured reaction rates via spectrophotometry. Plots of change in absorbance were used to determine the rate law and the rate for the reaction.

The lab report asks:

  Suggest another method, other than spectrophotometry, for determining the reaction rate measured in this experiment.

Knowing little about measuring rates, I said one could measure the enthalpy and entropy of the reaction at a given temperature, and use those to calculate the rate constant. This is based off of the equation

$$\ln\frac{k}{T}=-\frac{\Delta H_\text{act}}{RT}+\ln\frac{k_\mathrm{B}}{h}+\frac{\Delta S_\text{act}}{R}$$

but, my professor said thermodynamics couldn’t be used to characterize kinetics. Also, reflecting on my answer, I didn’t really specify a technique.

What’s another technique that could be applied here?


texts: Can state of matter from liquid to gas maintain the same molecular structure in PE or in polymers in general, like water does?

texts:
If I’ve got a reactor containing PE-Polyethylene $(\ce{{C2}$H_\text{4})n$}$ (solid) and the rest is filled with nitrogen gas. The system is closed.  Supposing we have an initial temperature of $30~\mathrm{°C}$ and gradually increase the temperature to $180~\mathrm{°C}$. We’ll observe a change in state of the PE, passing from solid to liquid, at this point the molecular structure is the same.

If temperature is increased beyond $250~\mathrm{°C}$ pyrolysis will occur on PE and syngas will be produced, at this point the gas molecules will have different structures compared to $(\ce{{C2}$H_\text{4})n$}$, thus "we’ll not observe" a change of phase from liquid to gas maintaining  the same molecular structure. Gas molecules will nave n types of molecular structures.

Is it possible by varying PVT to have a change of phase, from liquid to gas, of PE and maintain the same molecular structure. Just like with water->vapor?
If this is not possible, why? what are the topics to study?


texts: Calculating the molar iodine concentration of a CT contrast agent

texts:
I want to calculate the molar concentration of Iodine in a CT contrast agent.

Name: Isovue 300 (Iopamidol - $\ce{C17H22I3N3O8}$)

Molecular weight: $777.09\ \mathrm{g \ mol^{-1}}$

The part that confuses me is this:
"Each $\mathrm{mL}$ of Isovue-300 (Iopamidol Injection $61%$) provides $612 \ \mathrm{mg}$ iopamidol with $1 \ \mathrm{mg}$ tromethamine and $0.39\ \mathrm{mg}$ edetate calcium disodium. The solution contains approximately $0.043\  \mathrm{mg}$ ($0.002\ \mathrm{mEq}$) sodium and $300\ \mathrm{mg}$ organically bound iodine per $\mathrm{mL}$." (source: https://www.drugs.com/pro/isovue.html)

Each molecule of Isovue contain 3 $\ce{I}$ atoms. So if I calculate the molar concentration (300 mg/ml / 777.09 g/mol * 1000 = 386.1 mM), do I need to correct for this?

I am sorry for this basic question, but I cannot find the answer on the manufacturer's website or elsewhere.

Thank you all in advance


texts: Significant figures addition vs multiplication

texts: I was finding the molecular weight of $\ce{Br2}$ the other day and noticed that if I add the weight of $\ce{Br}$ to itself, $79.90+79.90=159.80$, that answer for the weight has $5$ significant figures. But if I just multiply the weight by $2$, $79.90 \times 2 = 159.8$, the weight has $4$ significant figures. If adding something to itself is the same as multiplying it by $2$ mathematically, which accuracy is more justifiable for my calculations in cases like this?


texts: Calculating the heat capacity of a calorimeter

texts:
I've been struggling with this problem that I can't seem to figure out. I think I know how to solve it but I think there's missing information.

  The combustion of 1 mole of glucose $\ce{C6H12O6}$ releases $\pu{2.82\times10^3 kJ}$ of heat. If $\pu{1.25 g}$ of glucose are burnt in a calorimeter containing $\pu{0.95 kg}$ of water and the temperature of the entire system raises from $\pu{20.10 ^\circ C}$ to $\pu{23.25 ^\circ C}$. What is the heat capacity of the calorimeter?

I think I need the specific heat of glucose (which I haven't found yet), but also I don't know why they give me the heat released by 1 mole of glucose.  I need to know the method of how to solve such problems.


texts: Computing accurate vibrational and rotational contributions to the free energy of transition states and loosely bound complexes

texts:
Recently I have been dealing with a lot of transition states and relatively loosely bound ion-dipole complexes and I have some trouble figuring out how to make sure that the rotational and vibrational contributions to the Gibbs free energy are as accurate as they reasonably can. (I am using Gaussian 09 rev C)

I am using MP2/aug-cc-pVTZ, based on literature results it should be in close agreement with even better methods for the type of molecules I am working with.
First I have optimized the geometry to verytight convergence, then reoptimized it with verytight, CalcAll to make sure the geometry is as converged as possible, and get the thermochemistry output at the same time.
I have once read in a CCL post, that tightening SCF convergence can increase the accuracy of analytic derivatives, so I am performing all calculations with SCF=Conver=12.

My concerns are mostly related to having a number of low frequency modes, and the possibility of coupling between vibrations and rotations.
For example, in the case of the transition state between $\ce{MeCl + F-}$ and $\ce{MeF + Cl-}$, I have three low frequency modes: 258.4867 $cm^{-1}$, 258.4867 $cm^{-1}$ 303.2302 $cm^{-1}$ (and of course an imaginary frequency). Sure enough, Gaussian warns that:

  Warning -- explicit consideration of   3 degrees of freedom as vibrations may cause significant error

Based from what I gathered from various sources, this means that these low frequencies have significant uncertainties in them, and they may or may not be internal/hindered rotations. I have ran a calculation with Freq=hindrot but it did not identify any of the modes as rotations. However, the Gaussian manual says that the hindered rotor analysis is not always successful at finding rotations when transition states are involved.

My other concern is the validity of the rigid rotor approximation for molecules having low frequency modes (ie. low force constants). My intuitions tell me, that the lower the force constants in a molecule, the worse are the errors caused by the centrifugal distortions of the molecule.

So my actual questions are:

1.What is the proper way to accurately handle low frequency modes? How does one make sure that they are not some sort of rotation, when hindered rotor analysis does nothing? If they legit low frequency vibrations, are they reliable? If they are not reliable how can they be corrected?

2.Do I have to be concerned about low frequencies also implying that the rotational contributions are also affected due to centrifugal distortion?


texts: Indigo and the Environment: is it that bad?

texts:
TL;DR: In what aspects are the products of the indigo vat dyeing process (sodium sulphate, sulphite and thiosulphate ions) harmful to the environment or to living beings?

I was recently looking into the wastewater created in the process of vat dying using indigo. I found out that since indigo is quite insoluble ($\pu{990\mu g}$ at $\pu{25^{\circ}C}$) in water for reasons of intra-molecular hydrogen bonding, a reducing agent like sodium dithionite ($\ce{Na2S2O4}$) is required, which gives leucoindigo by reducing indigo in an alkaline medium.

A related passage from a distantly related paper:

  For this process, sodium dithionite ($\ce{Na2S2O4}$) has been considered as a best reducing agent in traditional and industrial dying but the reducing agent releases sodium sulphate, sulphite and thiosulphate ions into the media. Those ions not only cause environmental concerns as major pollutants of the modern textile industry waste waters but they present also no negligible risks of toxicity against living organisms.

A few papers suggest that the "wastewater" generated by the process is not suitable for disposal as such. But I still find no clarity, despite prolonged efforts at scouring journals, in why these exact ions cause the suggested adverse effects to the environment. I would be grateful if someone could please share any relevant knowledge.

These ions appear pretty harmless to me..

References:

The role of natural indigo dye in alleviation of genotoxicity of sodium dithionite as a reducing agent, Bektas I, Karaman S, Diraz E, Celik M, Cytotechnology, 2016 Dec; 68(6): 2245–2255, DOI: 10.1007/s10616-016-0018-7

BONUS: Are there any other harmful substances or environmental hazards in this nice indigo broth?


texts: how was freezing point depression dependence on solute concentration described?

texts:
Molarity is arguably the most intuitive descriptor for the "number of particles". But freezing point depression dependence on solute concentration is commonly described in textbooks as a function of molality. The same textbooks make it seem as if freezing point depression formula was determined empirically, in which case, it should take take only a few corrective factors to change it into a dependence on molarity. (In fact, I wouldn't be surprised to learn that some correction factors should be used to make the currently  formula more accurate. That is often the case with empirical formulae.)

So is it really the case that using molarity would make the formula dependent on solute nature, or was molality used for convenience?


texts: Are rate constants for water exchange of transition metal aqua-complexes tabulated anywhere ? I haven't been able to find a resource which is anywhere near comprehensive.


texts: Derivation of formula for Hydrolysis constant

texts:
While studying acid-base equilibrium I thought I would derive the formula for hydrolysis constant myself. But I ended up getting a weird result and I am not able to understand where I went wrong.

The equilibrium constants for reactions that tend to favour products are large. As the concentration of the reactants decrease the equilibrium constant slowly should move toward infinity. For example the ionisation of strong acids is taken to be a reaction that goes to completion. According to my understanding the equilibrium constant $K_\mathrm a=\infty$. The equilibrium constant for its reverse reaction would be zero. Similarly the equilibrium constant for the ionisation of salts should be $K_\mathrm s=\infty$.
Let us consider the reaction $\ce{HA + BOH <=> AB + H2O}$. This can be carried out in a number of steps:
$\ce{HA <=> A- + H+}$  with $K_\mathrm a$
$\ce{BOH <=> AB + H2}$ with $K_\mathrm b$
$\ce{H+ +OH- <=>H2O}$ with  $1/K_\mathrm w$
$\ce{A- +OH1+<=> AB}$ with $1/K_\mathrm s=0$
So the hydrolysis constant should be
$1/K_\mathrm h=K_\mathrm aK_\mathrm b/(K_\mathrm wK_\mathrm s)=0\cdot K_\mathrm aK_\mathrm b/K_\mathrm w=0$
hence $K_\mathrm h=\infty$
I am sure there is something I havent understood well and hence I've ended up on this result. Can somebody explain where I am wrong?
Note: In most proofs the equilibrium constant of ionisation of salts is not considered but I see no reason to not consider it.


texts: Why PDMS microfluidic devices are usually bonded with glass slides?

texts:
I note that many PDMS microfluidic devices are plasma-treated to be bonded with glass slides, despite that the wettability of PDMS and glass are drastically different.
I wonder that isn't there any consequence that the surface property of the bottom and top of the microfluidic channels are different?
For example, in many microfluidic droplet generators, some channels should be turned hydrophilic, while some channels should remain hydrophobic. Then what would happen in those hydrophobic channels, since the bottom of these channels is glass (hydrophilic)!
Thanks in advance!


texts: How to find oxidation state of Co and Cr in [Co(NH₃)₄(NO₂)₂][Cr(NH₃)₃(NO₂)₃]?

texts:
Which of the following options represents the oxidation state of $\ce{Co}$ and $\ce{Cr}$ in the given complex?
$$\ce{[Co(NH3)4(NO2)2][Cr(NH3)3(NO2)3]}$$
(A) $2, 3$
(B) $3, 2$
(C) $3, 3$
(D) $2, 2$

I am unable to judge the net charge on complex when it breaks into ions and therefore I am having trouble with this question. I assumed that some unknown charge with opposite signs must be on the complex ions.


texts: Do modern dispersion-corrected DFT methods give more accurate molecular geometries?

texts:
I was discussing with a colleague the use of modern dispersion-corrected density functionals. I take it almost as a given that the methods generally produce "better" (for some definition) geometries, in addition to more accurate predictions of thermodynamic and other properties.

Naturally, since the dispersion correction involves intermolecular interactions (e.g., van der Waals complexes), they should do better than "regular" functionals. I'm curious about intramolecular geometries.

Are there any benchmark comparisons on bond lengths, angles, etc. comparing different computational methods (DFT and otherwise) to crystal structure or other geometries?

In other words, how accurate are different computational methods at getting geometric properties of individual molecules?


texts: Is there an edible version of nylon string?

texts:
I'm working on a project where I have to check the feasibility for product ideas. It has to connect other parts and float on the water's surface.

My friend thought that maybe glass noodles would be thin and transparent enough to work in this product. Maybe there is another option that maybe is even water-soluble.

I also looked at PVA, but I don't think it is edible.

Thanks for any suggestion.


texts: aldehydes are easily oxidised but ketones are not

texts: Aldehydes are easily oxidized to carboxylic acid but ketones are difficult to oxidise. Most books say that the hydrogen directly bonded to the $\ce{C=O}$ in the aldehyde is what aids the oxidation process. However, can someone please tell me why this is so.


texts: So I've got a relatively simple question; I'm not currently taking any courses in chemistry but while I was helping someone review a quiz I came across a question we couldn't figure out. According to the Bohr Model, is the energy required to excite an electron from the n=3 to n=4 orbit generally greater or less than the energy required to go from n=4 to n=5? Also, why is this so? I can't seem to find a clear answer anywhere online, as just about every result involves directly computing energy required to bump the electron up a few levels in very specific cases.


texts: The melting point of gold was changed from 1063 deg C to 1064 deg C in an ASTM procedure that uses the melting point of gold as the end point for a test.  Did the melting point change somehow or was there an error in the ASTM method?


texts: Polar rearrangements: What is this reaction called?

texts: I have been trying to find more information about the given reaction but cannot seem to find it? I want to know the name so I can read up more information on it. Can anyone help?


texts: Why does 1,2-dichloro-4-nitrobenzene undergo SNAr para and not meta to the nitro group?

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In the reaction of 1,2-dichloro-4-nitrobenzene with sodium ethoxide, why does ethoxide end up substituting the chlorine para to the nitro group rather than the chlorine meta to the nitro group?

I think that C–2 should be the most electron-poor carbon (and hence prone to nucleophilic attack) since it experiences a combined electron withdrawal from the nitro and chloro groups flanking it. Shouldn't the nucleophilic ethoxide anion attack there instead?


texts: How to calculate crystal field stabilisation energy?

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How to calculate it? I know that it depends on the coordination compound and the number of electrons present in t2g and eg orbitals and the final answer is expressed in terms of crystal field splitting parameter. But, how to know how many electrons are there in t2g and eg orbitals?

I think rather than a broad answer and example would help. So, consider the compound $\ce{[Ni(CO)4]}$ and how to calculate CFSE for it?


texts: Does battery self discharge when connected?

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I am an electric engineer, and I read about battery self discharge phenomenon. I was wondering whether a battery self discharge rate is the same when it is unconnected (i.e. in storage) and connected (i.e. when it is plugged into a device and being discharged "normally").
In other words, when I calculate battery life time for a product, should I take add the rated self discharge of a battery to the general current calculations or not? And also-is the answer similar to all types of battery?


texts: Does the Fermi level correspond to the highest occupied energy level?

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I know that, in the band structure of a solid, the Fermi level is the energy level at which there is a 50% probability of finding an electron (at thermodynamic equilibrium), and that it doesn't have to correspond to an actual energy level (ie it's in the band gap in an insulator).
But Atkins and Shriver's Inorganic Chemistry doesn't mention this and instead defines it as the highest occupied energy level at 0 K. (page 103, 5th edition)
I was wondering if these definitions are actually equivalent. If so, can you explain how? Given the fact that in an insulator the Fermi level is in the band gap, it seems like at best the definition in Atkins is oversimplified.


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Imagine you have two ingredients - 45 grams of 60% ethanol, and as much water as you wish. The only accurate tool you have is a scale, which measuring error is up to $\pm \pu{1gram}$. How would you create five different solutions of 1, 2, 3, 4, and 5% ethanol?

It can be a solution of % ethanol by volume or by weight, depending on which can be created more accurately with the tools at hand. It might be super easy to you, but as an electrical engineer the logic and math eludes me.


texts: Can toluene be used as a solvent for nucleophilic substitution?

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This is a continuation to a previous question of mine regarding a change to a one-pot procedure for the preparation of Wellbutrin that I performed in college last semester. Could toluene have been used as the extraction solvent for the a-bromoketone and for the nucleophilic substitution? The procedure we were given used DCM and then removed it under vacuum for a solvent switch to NMP. Also, what was the reason for this? Could a mixture of NMP and DCM have been used?

Previous question: Suggestions for solvents capable of efficiently performing alpha-bromination and nucleophilic substitutions


texts: Organic reaction of dry ice and Grignard reagent

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Which of the following product is formed in the reaction $\ce{CH3MgBr}$ in DryIce/acid?
  A) $\ce{CH3COOH}$
  B) $\ce{CH4}$
  C) $\ce{CH3OH}$
  D) $\ce{CH3CH2CHO}$

My answer is A, since dry ice is $\ce{CO2}$ and it has one carbon atom and reactant has one carbon, so in all the product should have two carbon atoms, which is option A.

Am I correct?