texts: What is the mechanism of benzyl ether hydrogenolysis?

texts:
The mechanism for the hydrogenation of alkenes or alkynes using Pd/C is fairly well explained to involve the absorption of hydrogen onto a metal's surface followed by the addition of that hydrogen into the π* orbitals; however, I am having a hard time understanding or finding any literature on the mechanism for the simple hydrogenolysis of benzyl ethers.
I would not expect this to involve the same surface chemistry as the hydrogenation of alkenes/alkynes due to the geometry of the C–N and C–O σ* orbitals; however, the catalyst used, Pd/C, is heterogeneous, so I don't know what other mechanisms could be possible. I found a paper1 that reported the mechanism for hydrogenolysis involving a homogenous catalyst was an oxidative addition followed by reductive elimination; however, I am not sure if this is the same mechanism that applies to benzyl ether cleavage with Pd/C.

Martínez, A. G., Alvarez, R. M., Aguirre, J. A., & Subramanian, L. R. (1986). Mechanism of hydrogenolysis. Part 1. Catalytic hydrogenation of vinyl and aryltrifluoromethanesulphonates. J. Chem. Soc., Perkin Trans. 1, (0), 1595–1598. doi:10.1039/p19860001595


texts: Why isn't my electrochemical cell producing its potential voltage

texts:
For a school project, I am testing how concentration affects the voltage output of three metals. So I am building voltaic cells with 0.1 M copper nitrate and 0.1 M, 0.01 M, and 0.001 M of zinc, aluminum and nickel nitrates as the electrolyte solutions. For the cells with zinc and copper, I found that the voltage produced was generally fairly close to their theoretical value of 1.10 V with the lowest voltage produced being 0.95. However, for aluminum and nickel, I have found that they are very far off from their theoretical values of 2.00 and 0.57 respectively as I have only reached a maximum voltage of 0.50 for aluminum and 0.20 for nickel.
I am using a porous cup and have made sure all of the electrodes are thoroughly sanded before each trial. I am fairly confident the issue is not related to the concentrations, or to the porous cup. At this point, I just have no idea why it isn't working. I read a similar question on here suggesting that the issue might be that aluminum does not easily dissolve in NO3 and I was wondering if the same was true for nickel.


texts: Why can zinc porphyrins assume 5 coordinate geometries?

texts: It has been reported that 5-coordinate geometries are possible and stable for Zn(II) porphyrin complexes. How do these complexes form and why are they stable when other 5-coordinate geometries of Zn(II) and other d10 metals are not stable?


texts:
How to make hydrogen peroxide into a gel or just simply really thick and it has to be able to be in your mouth?

The only thing i have came up with is (Gelatins).
What should i use?


texts: Will there be a temp change in free expansion

texts:
I did a little thought experiment, where I place an infinitely long beaker filled with some gas, which has a moveable piston at the open part. So if I place this beaker in vaccume, there will obviously be no work done on the system and hence no loss of energy due to the work done by the system (because the int pressure of the energy will obviously push the piston upwards).
So here's my main question:
If in the Beginning, let's say we have a certain amount of gas placed in the beaker such that the piston is just 1 cm above the base. But after infinite time the lid will probably be at infinity. So if a t=0, the gas occupies a limited space, won't the collisions be high and hence kinetic energy be high, which would mean the temperature of the system is high? But at t= infinity, the gas would occupy an infinite amount of volume which would mean that there are less collisions, so wouldn't this reduce the velocity of the molecules, hence reduce the kinetic energy, hence reduce the temperature?
I feel something is wrong over here because mathematically, I know there shouldn't be any change in int energy, therefore the temperature. So how do we justify this experiment?


texts:
Having made diy pcb 's at home I have used things like tinnit which is a clear liquid . When the pcb is dropped into them , a layer of tin forms on the exposed copper regions on the pcb . I was wondering if someone could explain what is happening or if someone could give an equation .

Here is a video of the process on youtube https://www.youtube.com/watch?v=wOqkI-S-wdI


texts: Why does charcoal absorb smells from the air, and where do those smells 'go' once absorbed?

texts:
I've read that using blocks of charcoal can remove some odors from the air by placing them in the vicinity of the odors. (Maybe not as efficiently as other forms of carbon, as pointed out in the comments of that link, but something nonetheless.)

What is the chemical process by which charcoal can do that, and once the odors are 'gone', where do they 'go'? In the case of 'toxins in gases', what typically is done to them upon 'deodorizing' by the charcoal block - are they collected, neutralised / transformed upon contact, or something else?


texts: Starting from any a,ß-unsaturated carbonyl compound, how would you prepare the following Organic compound?

texts: Is this correct so far? Is there any other way to do this? Was it wrong of me to add KCN instead of HCN? Any help would be appreciated, thank you!


texts: Ground state conformation of dimethyl disulfide

texts:
What is the ground state conformation of dimethyl disulfide ?

The two which seem reasonable to me are trans to avoid methyl-methyl gauche interactions or gauche due to sulfur donation into the S-Me sigma antibonding orbital.

I found a discussion in this paper but it doesn't seem to really answer the question definitely.


texts: Why would rinsing the flask with acid in this experiment affect its accuracy?

texts:
The following question is #21 from this test form (PDF link):

The apparatus in Figure 4 was set up to measure the time taken for $\pu{20.0 cm3}$ of sodium thiosulfate solution to react with $\pu{5.0 cm3}$ of hydrochloric acid in a $\pu{100 cm3}$ conical flask at $\pu{20 °C}$. The timer was started when the sodium thiosulfate solution was added to the acid in the flask. The timer was stopped when it was no longer possible to see the cross on the paper.

What is likely to decrease the accuracy of the experiment? [1 mark]
A) Rinsing the flask with acid before each new experiment.
B) Stirring the solution throughout each experiment.
C) Using the same piece of paper for each experiment.
D) Using different measuring cylinders to measure the volumes of acid and sodium thiosulfate

The answer given as correct is (A). Why is rinsing the conical flask with acid likely to decrease the accuracy of the experiment? I would imagine that stirring the solution, option (B), introduces error since the rate of stirring is difficult to control.


texts: How to make solution of specific concentration with non-stoichiometric hydrate?

texts:
I am currently working with a drug molecule known as Amiloride $\ce{HCl}$ and it seems to be a non-stoichiometric hydrate.

How would I go about making a solution with a specific concentration of Amiloride $\ce{HCl}$? I know its anhydrous molecular weight but if I don't know how much water is in the solid crystals how can I get a specific concentration?


texts: The effects of acetic acid on porous concrete brick and mortar joints for someone who has no understanding of chemistry

texts: I mistakenly applied a patio cleaner containing acetic acid to my porous concrete facing brick thinking it was biocide. The concentrate solution has a ph of 3 and I diluted it to one part concentrate and three parts water. About three hours later, having realised my mistake, I flushed it with water. I repeated this process the following morning and also on the morning after that. The bricks now appear to be dry. I have been told that the pore structure of the type of bricks I have is vital in protecting them from frost attack. I’m very concerned that the acid has damaged the brick and mortar joints and am wondering if the acid has now completely evaporated - one day after the last rinse. Is there anything more I can do to neutralise any residual acid? I would be very grateful for any information. Thank you.


texts:
I'm familiar with the fact that theoretical formulae are based on already known theory and are very frequently simplified (some equations don't include interactions between molecules for example) while the purpose of empirical equations (like polynomial equations) is just to follow experimental measurements even if it doesn't make any chemical or physical sense.

Which of these yield more accurate results (compared to reality)? What are the upsides and downsides of each group? Which are more universal? Which would require less compound-specific data (constants) to use it?

Edit: Removed van der Waals equation as an example of theoretical equations since, as pointed out by others, it's actually an empirical equation.


texts: Recently I saw a video which told me that Hydrogen has a valency of 1, i.e, Hydrogen can only bond with 1 other atom. But since hydrogen wants a complete shell, it can have 2 covalent bonds with 2 electrons. Please explain.


texts: How to calculate Debye length of a 2-1 electrolyte

texts:
I am given the Debye length to be 10nm for 0.001M KCl at 298K. I want to know its Debye length in 0.01M CaCl2. How can this be calculated?

I know that for 1-1, the Debye length is inveresely proportional to the root of its concentration. But how can I work out for electrolytes other than 1-1?


texts: How is it that earth's inner core is still solid?

texts:
Earth's inner core is made up of an alloy of Iron and Nickel.

The important note here is that it is solid.

The temperature at the inner core is about $5,763K = 5,490\text{ degrees C}$.

Now the melting point of both solid iron and nickel is about $1,500\text{ degrees C}$, and even though they are combined, I still think that $5,490$ is much greater then the melting point of the alloy.

Regardless, how is it that the inner core still stays solid? I would expect that at such higher temperatures, a phase change to liquid, or maybe even gas would occur.

Why does it not?


texts: My teacher says buta-1,2-diene is symmetric and hence optically inactive but I think it's the opposite, because allenes with an even number of double bonds are optically active because they have no plane of symmetry. Which answer is correct?


texts: Liquid with low specific heat and high thermal conductivity (relative to water)?

texts:
As the title suggests – does there exist a liquid with a lower specific heat then water but with a higher thermal conductivity?

I thought of this in the context of sous vide cooking: Ideally, the liquid involved would transfer heat to the food quickly (hence high thermal conductivity), but would also respond to quick changes in temperature (hence the low specific heat), reducing the risk / time of heater element overshoot.

So, are there such liquids? (preferable ones that stay liquid between 20 and 85 degrees Celsius).


texts: Is there any difference between thermal energy at room temperature in fluids(water) vs air?

texts:
Context of the question: I was reading on hydrogen bonds, specifically how close they are to the thermal energy of the fluids. So I googled the value of thermal energy at room temperature, which was $\pu{2.5 kJ/mol}$. Which is a difference of $10$ order of magnitude (H bonds are $\pu{23 kJ/mol}$), which makes sense to me given the time taken to break ($1$ to $\pu{20 ps}$) and reform a bond ($\pu{0.1 ps}$). That is how the question I posed in the title arised.

Since sea water can retain heat for longer periods of time, and they release it more slowly as well – what is the difference between thermal energy at ambient room temperature for gas (atmosphere) vs fluids (water), and how does this change with volume?


texts: In water, will sucrose be hydrolysed by water to form glucose and fructose molecules?

texts: If I dissolve sucrose sugar ($\ce{C_12H_22O_11}$) in water, would the water readily hydrolyse the sucrose sugar to form glucose and fructose sugars?


texts: Is sulfuric acid necessary for Kevlar synthesis?

texts: In the production of Kevlar, the 2 monomers needed for its creation are reacted in a solution. Due to it being water-insoluble, sulfuric acid is used. My question: Can other chemicals be used as well (for examplke salicyclic acid), or is sulfuric acid absolutely necessary? Is there maybe a benefit to using it, or is it simply the cheapest?


texts: Does hydrogen react with air at room temperature and pressure?

texts:
I have a container with 3% hydrogen and the rest is air. How fast will the hydrogen get oxidized by air?

How much will the reaction speed up with increased temperature?


texts: What is the correct term of a chemical formula for very large molecules if not just "chemical formula"?

texts:
I know that many molecules, wihch I as a non chemist, might define as "small" if their two dimensional diagram can be sketched on an A4 page, are often formulated;
That is → by one or more processes given a chemical formula;
Maybe after being isolated from a natural deposit or organism.

For example, here is such formula for vitaminB12 of the type hydroxocobalamin:

C62H89CoN13O15P

My problem

Whenever I examined a wiki article about a protein molecule, I understood it as too big to be represented in a "chemical formula", let alone in a two dimensional diagram on an A4 page, such as those I have described.

I though for example:

  As these are isolated molecules after all, they do have a "chemical formula" and should be standardly represented somehow.

  Such large molecules doesn't have to be proteins → maybe proteins and other molecules in similar size have different ways to be represented.

My question

What is the correct term of a chemical formula for very large molecules (such as proteins), if not just "chemical formula"?

From prior research I understand a "protein sequence" is the standard parallel for "chemical formula" in the context of proteins but I don't know about a standard parallel to such large molecules in general.


texts: Why is Gibbs free energy more useful than internal energy?

texts:
$$\mathrm{d}U<T\,\mathrm{d}S-p\,\mathrm{d}V=
\left(\frac{\partial U}{\partial S}\right)_{\!V}\,\mathrm{d}S
+\left(\frac{\partial U}{\partial V}\right)_{\!S}\,\mathrm{d}V$$

So for a change to occur at a constant entropy and volume, the internal energy must decrease. I get that this statement isn't useful because you can't control entropy in a lab. Furthermore, given that:
$$\mathrm{d}G<V\,\mathrm{d}p-S\,\mathrm{d}T=
\left(\frac{\partial G}{\partial p}\right)_{\!T}\,\mathrm{d}p
+\left(\frac{\partial G}{\partial T}\right)_{\!p}\,\mathrm{d}T$$
this shows that a spontaneous change at a constant pressure and temperature is accompanied by a decrease in Gibbs free energy – far more useful as these variables can be controlled.

However, since, for a spontaneous process, $\mathrm{d}U$ must decrease at a constant entropy and volume which is expressed by $\mathrm dU<T\,\mathrm dS-p\,\mathrm dV$. However, expressions for $\mathrm dS$ and $\mathrm dV$ can be expressed as a function of $p$ and $T$ making this inequality a function of pressure an temperature.
\begin{align}
\mathrm{d}U &<T\,\mathrm{d}S-p\,\mathrm{d}V\\
S&=S(p,T)\\
V&=V(p,T)\\
\end{align}

Sub in the total derivatives and factorize:
$$\mathrm{d}U<\left[T\left(\frac{\partial S}{\partial T}\right)_{\!p}
- p\left(\frac{\partial V}{\partial T}\right)_{\!p}\right]\,\mathrm{d}T
+ \left[T\left(\frac{\partial S}{\partial p}\right)_{\!T}
- p\left(\frac{\partial V}{\partial p}\right)_{\!T}\right]\,\mathrm{d}p$$
Thus, $U=U(p,T)$

This implies that for a spontaneous change at constant pressure and temperature the internal energy must decrease however this is not the case clearly. Does making the substitutions invalidate the inequality? Where is the fault in my reasoning?

So, what's the need for Gibbs free energy. Surely a spontaneous change at constant pressure and temperature is accompanied by a decrease in internal energy? There must be a fault in my reasoning, but where and why?


texts:
I'm thinking in the following experiment:

A) Two (non mixable (like water and oil)) liquids are going to lie in a container, in the extremes of the container there are two electrodes, those electrodes will have a potential difference $\Phi$. Just as the figure $1.a)$.

I'm looking for  some interesting liquids that mix, change of color when a voltage difference is present.

B) The next one is really similar, now there are some solid particle present, analogously I look for a mixture that has different properties when a voltage difference is present.

I'm a physics student that want to study different properties of mixtures when applying different voltage differences, and maybe study the diffusion of the solid particles when they mix, if the diffusion coefficient is grater, etc.

Any help with the liquids that has this property is really  appreciated.

Cross posted Physics stack Exchange


texts: Why are wavefunctions with same principal quantum number and different azimuthal quantum number orthogonal

texts: The value  turns out to be zero . This is understandable since they are completely independent of each other and also perpendicular in real space. But also turns out to be zero . How do I justify the orthogonality of the s and the p levels?


texts: How to determine toxicity of a substance?

texts:
I often read description of various compounds or elements as being poisonous. Now I know that through experience we have discovered the toxicity of various substances like lead, chlorine or phosgene etc. We know nitrogen isn't poisonous as its present in the atmosphere etc.

What I wanted to ask is whether there is a perfectly analytical or experimental way through which chemists determine whether a newly discovered substance is or isn't poisonous? Or is it always found out only by exposure to humans (which I don't think is always possible)? Or perhaps whether such an information can't always be deduced?

I think animal testing is a possible (but immoral) method but again some substances could be harmful to them but harmless to us.


texts: Entropy change during irreversible process

texts:
Entropy change is defined as $\Delta S = \int \frac{\delta Q_{rev}}{T} $, where $Q_{rev}$ is heat transferred through a reversible process.  I’m a little confused how this works, so I have a couple of related questions which I hope will clarify what’s going on.

If a reversible process is defined as $\Delta S = 0$ then how can this integral be non-zero for a reversible process?  Or is it that just $\Delta S_{Univ} = 0 = \Delta S_{sys} + \Delta S_{surr}$ and therefore $\Delta S_{sys} = -\Delta S_{surr} \iff T_{sys} = T_{surr} $, in which case

How would one calculate it for an irreversible process, in particular, some heat, Q, transferred across a finite temperature difference?
I would try (considering isothermal transfer between infinite temperature reservoirs)
$$ \Delta S_{Univ} = Q \big( \frac{1}{T_{sys}} - \frac{1}{T_{surr}} \big) $$
But this is no longer reversible, so I need to do something else?

Since entropy is a state function, is the entropy change through any process that is irreversible, but between equilibrium states, equivalent to $\int \frac{\delta Q}{T}$ through a reversible process?

Is this equivalent to pretending I’m doing 2 reversible transfers to some fictitious bodies, the first taking Q reversibly from the system to the fictitious body, both at $T_{sys}$, and then magically dropping the fictitious body to $T_{surr}$  and transferring the heat Q to the surroundings?
If so, why use $\delta Q$ rather than $dQ$?  My understanding was that $\delta Q$ was for path-dependent processes, but there is only one fixed (adiabatic) path for reversible transfer?

Sorry for yet another entropy question, thanks in advance!


texts: I have been reading some papers and one mentioned "4-fold triethylamine based on PEG-diol end groups", "4-fold acryloyl chloride." What is the meaning of "4-fold" in those compounds? Also, can I find these chemicals for sale or must I synthesize them myself?


texts: Example of an endothermic reaction that can sustain itself for at least an hour?

texts:
Recall that in physical chemistry, the spontaneity of a reaction at constant pressure and a given temperature $T$ can be quantified by the Gibbs free energy

$$\Delta G = \Delta  H - T \Delta S$$

A reaction is spontaneous if $\Delta G < 0$. For an endothermic reaction to be spontaneous, $\Delta H < 0$, $\Delta S > 0$ and $|\Delta H|< |T\Delta S|$

Now suppose we monitor the rate of change of $\Delta G$ as the reaction progressed. This means

\begin{align}
\frac{\mathrm d\Delta G}{\mathrm dt} & = \frac{\mathrm d\Delta H}{\mathrm dt} - \frac{\mathrm d(T \Delta S)}{\mathrm dt}\\
\frac{\mathrm d\Delta G}{\mathrm dt} & = \frac{\mathrm dT}{\mathrm dt}\left(\frac{\partial \Delta H}{\partial T} - T\frac{\partial \Delta S}{\partial T}- \Delta S\right)
\end{align}

Now suppose for simplicity $\Delta H$ is roughly constant with temperature. Then:

$$\frac{\mathrm d\Delta G}{\mathrm dt} = \frac{\mathrm dT}{\mathrm dt}\left( - T\frac{\partial \Delta S}{\partial T}- \Delta S\right)$$

Thus for $\frac{\mathrm dT}{\mathrm dt} < 0$, a reaction to be self sustaining indefinitely if the following holds for all $t > 0$

\begin{align}
- T\frac{\partial \Delta S}{\partial T}- \Delta S & > 0\\
- T\frac{\partial \Delta S}{\partial T}  & > \Delta S
\end{align}

In all closed systems, entropy will eventually maximises according to the second law, thus there will be a point where $\frac{\partial\Delta S}{\partial T} < 0$ (i.e. the increase in entropy as the reaction progressed will slow down over time) until the reaction stops (thus explaining why both exothermic and endothermic reactions will eventually go to completion)

Therefore, my question on self sustaining endothermic reaction that last for hours is boiled down to finding a time $t>0$ such that the above inequality holds in the order of hours, given a $\Delta H$ as positive as physically realisable

  Any example of an  endothermic reactions that has $\Delta H > 50{-}100\ \mathrm{kJ\ mol^{-1}}$ and can sustain itself in the order of hours?


texts: Separating a powdered mixture of Zinc Oxide and Silver Oxide

texts:
I have some powders that contain silver, $\ce{Ag2O, ZnO}$ and maybe some $\ce{AgO}$
Can I wash powders with $\ce{NaOH}$ to remove $\ce{ZnO}$ (as Sodium zincate) without any silver or silver oxides loss?


texts: What is the expected number of rings obtained in the following ring formation process?

texts:
Refluxing, say, one mole of 1,5-dibromo-pentane with excess ammonia in ethanol can result in the formation of rings. (e.g. $1\lambda^2$-piperidine)

However, it is also possible for the 1,5-dibromo-pentane molecules to be connected together, forming longer chains without forming rings. The longer chains can be reacted again to form larger rings. So in theory, we can have rings that are arbitrarily large.
This is about the rings' size distribution
Question: What is the expected number of rings (large and small) after the reaction finishes? How many of the rings are $1\lambda^2$-piperidine? Generally, is there a mathematical distribution that describes the expected number of rings of any given size?


texts:
Is the mechanism similar to the reaction of $\ce{SOCl2}$ with alcohols?
If not, then how is it different? We have been taught about the latter at school but my friend quizzed me about $\ce{SO2Cl2}$.

Please give the detailed reaction mechanism.


texts: Why don't Schools follow latest IUPAC for naming groups?

texts:
In high school I am taught that Group 7 were halogens and Group 8 were noble gases, and Group 3 the boron group, Group 4 was carbon group, etc. Then when I looked up the groups, I found that noble gases were group 18, halogens were group 17, Group 7 was the manganese group, ...

The school said that their numbering is based on counting valence electrons, and the transition metal columns have no business in their lessons.

So schools don't use IUPAC conventions.

How standard is their group name scheme?


texts: Help balancing reaction between Iron (II) chloride and potassium phosphate

texts:
Very rusty with chemistry and looking to review some basics. Came across the following:

  Iron(II) chloride and potassium phosphate react. Write and balance the molecular, ionic, and net ionic equations.

What I have so far (guessing, basically):

$$\ce{FeCl2 + K(H2PO4) -> KCl + Fe(H2PO4)2}$$   [still need to balance but correct right hand side?]

I can't remember the exact rules for forming the right hand side. I just put this in place to match ion charges. What prevents me from writing the right hand side as something else entirely (not sure what but I'm asking, "well, couldn't I figure something out if I break everything apart and re-arrange into another option?").

EDIT: Additional Question Below

Ok, so assume the above reaction was balanced (it's not) and valid. Then, my question is does the reaction go both ways ($\ce{<-->}$)? If so, when/why/how? I'm trying to think back many years ago and it has something to do with "reactivity" and the row of the elements on the periodic table, correct? I'm going to look into it more myself but if someone has a quick "30 second" answer I'm sure it'd be of help to me!

[Assuming this is OK and valid in the forward direction. Again, needs to be balanced.]

$$\ce{FeCl2 + K(H2PO4) -> KCl + Fe(H2PO4)2}$$

[Is this ever ok/possible?]

$$\ce{KCl + Fe(H2PO4)2 -> FeCl2 + K(H2PO4)}$$


texts: Products for the hydrogenation of the cycloalkene in (3R,4R,5S)-4,5-diamino-3-(pentan-3-yloxy)cyclohex-1-ene-1-carboxylic acid

texts:
Write the products (more than one) for the hydrogenation of the cycloalkene ring in (3R,4R,5S)-4,5-diamino-3-(pentan-3-yloxy)cyclohex-1-ene-1-carboxylic acid. Reagents are molecular hydrogen with Pt catalyst.

My problem here is that the question implies there are several products for hydrogenation of the cycloalkene. I only see one product, where each end of the alkene obtains a hydrogen, and the pi bond is gone. How can a hydrogenation of this alkene result in more than one product?


texts: Why is the first member of group IVA and the second member of group VIA show stronger tendencies to catenate compared to the other group members?

texts: catenation is a process by which a molecule or an atom forms a straight or repeating chain with other atoms.in carbon it has 4 electrons in the outer most energy level hence can form chains repeatedly


texts: How does boiling water affect its hardness?

texts:
Does boiling water reduce its hardness, or on the contrary, increase it?

It seems there are ambivalent phenomena at play here:

boiling will evaporate pure water, thus increasing the concentration of minerals including calcium, thereby increasing hardness
boiling will remove $\ce{CO2}$, making apparently $\ce{CaCO3}$ precipitate, thereby reducing hardness

This is based on rather uncertain sources, as I didn't find any better, and maybe I missed other aspects.

I would appreciate any clarification, but I understand that the answer might depend on the context and type of water considered.


texts: How would someone in 1917 describe elements 43, 61, 72, 75, 84, 85, 87, 89, and 91?

texts: https://books.google.com/books?id=aaELAAAAYAAJ&printsec=frontcover#v=onepage&q&f=false Notice the list of elements on pages 62–63. It includes a short description of each element's "Nature under Ordinary Conditions." I am curious to know what the author might have written for elements 43, 61, 72, 75, 84, 85, 87, 89, and 91 (based on 1917 knowledge; for those which hadn't yet been discovered, some properties could be told from the element's position on the periodic table). Would people be willing to suggest period-appropriate descriptions for them?


texts: "Limit test" vs. "Titration" in a pharmaceutical guide

texts:
From the "Technical guide for the elaboration of monographs" by EDQM, edition 7, 2015, page 35:

  Where the introduction of tests for foreign anions in organic substances is considered then a single one, either for chlorides, sulfates or − less commonly − nitrates, will usually suffice even when several could theoretically be present. The test is then to be carried out on the most abundant anion. When a test for chlorides is considered, up to 1000 ppm (0.10 %), a limit test should be used rather than titration.

I don't understand this. Isn't titration one of the possible ways to perform a limit test (to check whether the chloride content is within the specified limits)?

Maybe my understanding of "limit test" is flawed?


texts: Will trenbolone acetate in the presence of methanol yield trenbolone acetate if distilled water is subsequently added thereafter?

texts:
I have 2 grams of trenbolone acetate. I was told to add it to 20 ml of methanol. Then wait until it is fully dissolved. Then distilled water is to be added yeilding a precipitate that is supposed to still be trenbolone. Can anyone shed light on this?
Here is the link.


texts: Is there any difference between Meprobamate and Equanil?

texts:
My textbook mentions Meprobamate and Equanil separately, under Anxiolytic drugs and even provides two (not-so) different structures to back their claim.

However, Wikipedia would beg to differ:

  Meprobamate — marketed as Miltown by Wallace Laboratories and Equanil by Wyeth...

Which would naturally imply, that Meprobamate and Equanil are...the same thing. ಠ_ಠ

A quick search with Google Images got me this:

Now this particular textbook I use has, over the years, gained notoriety among several generations of us students as the Mater Omnium Errorum. So in all likelihood, my textbook's the one that's wrong here.

But since I'm not a Pharmacologist, I'd appreciate it if someone could verify if Meprobamate and Equanil are the exact, same, chemical.

I tried Google, but that endeavor wasn't particularly helpful.


texts: How do you calculate the correct charge on F after F2 dissociates?

texts:
When you ionize $\ce{F2}$ to $\ce{F2^5+}$, it quickly dissociates. Experiments show that the products of dissociation are $\ce{F^2+}$ and  $\ce{F^3+}$.

I have tried to model the dissociation of $\ce{F2^5+}$ using Gaussian$09$ (DFT), specifying a 10 Å separation between products.

No matter which functional I use ($\omega$B97X, PBE, M06,etc.), I get a $+2.6$ charge on one $\ce{F}$ ion and $+2.4$ on the other. Why don't these functionals give $\ce{F^2+}$ and $\ce{F^3+}$ ions the corresponding formal charges as shown by experiment? And how do you get the correct charges?


texts: Reaction of 1,2-diketones with periodic acid

texts: $\ce{HIO4}$ can oxidise alcohols. But does $\ce{HIO4}$ undergo any reaction/act as oxidant with 1,2-diketones?


texts: Can a double bond extend beyond the plane and if so, how would it be drawn?

texts: Can double and triple bonds, etc., extend beyond the plane in a Lewis structure, and if so, how are they represented? I.e., how would 1 and 2 in this image be drawn if they were doubles or triples?


texts: Anhydrous ammonia vapor-liquid equilibrium

texts:
I have been given a anhydrous ammonia vapor liquid system in an air-tight container where the pressure is 30 bar and the temperature is 30 degrees. They claim the system is in equilibrium, which I have two doubts about.

The vapor pressure for anhydrous ammonia at 30 degrees is less than 30 bar, how is it possible to have this pressure in the given system?
Will the volume ratio of vapor phase with regards to liquid phase affect equilibrium? If so, then how?


texts: Could UV lasers be used to split CO2 and H2O?

texts: I was wondering whether intense UV light, tuned to the correct wavelength, could be used to split carbon dioxide and water molecules as a first step towards synthesizing liquid fuels.


texts: When we look at atomic mass, for example, $\ce{^134Ba}$ (barium) has a mass of $133.90 \,\mathrm{Da}$. Why is this rounded to $134 \,\mathrm{Da}$? This is shown in my book.


texts: Is there a element that shows this pattern of boiling point?

texts:
Is there a compound that turns to gas at a certain temperature but if heated more turns back to liquid and if heated more than turn to gas?

Does it exist naturally? Has a such a substance be found? Can such a substance exist? if yes, then why?

Why couldn't at some temperature molecules interact in such a harmony that they actually cling together?


texts:
Heat is the total kinetic energy of all atoms of the system. When work is done on the system it means that a part of system kinetic energy is used to do the work, and this work makes the surrounding warmer.
So "$\Delta U$" of the system is equal to "$Q$".
And now, why we use the work of the system in: $\Delta U = Q + W$?


texts: What are complete active space methods and how are such spaces defined for molecules?

texts:
I am new to computational chemistry and would like to know about the active space and inactive space terminologies in MCSCF type calculations.

For understanding this I have four systems:

$\ce{H2O}$
$\ce{Be}$
$\ce{Be(OH)2}$
$\ce{NO3-}$

For above atom, molecules and ion what would be the CAS space configuration (which is typically written as eight digits) separately for inactive and active space. If you could give explanation then it will be useful.


texts: How to temporarily hide hydrogen atoms in Molden?

texts: I am visualizing some molecules with Molden. Is there a way to hide hydrogens, without deleting the hydrogen entries from the structure file?


texts: Why is it difficult to measure the pH of environmental water samples accurately (near 7)?

texts:
I've read in several places (edit: 1, 2, 3, 4, 5, 6, 7, 8. 9, 10, 11, 12) that there are many practical factors that make accurate pH measurements of roughly neutral environmental water samples more challenging than significantly basic or acidic samples.

Since the glass probes are sensitive fairly specifically to hydrogen or hydronium activity, why would concentrations around $\ce10^{-7}$ be more challenging than a much higher or especially much lower concentration, say $\ce10^{-10}$?

Discussions of the problem seem to center around issues related "solutions of low ionic strength", so a basic solution near pH 10 and a buffered solution near ph 7 would both have less practical measurement issues than a non-ionic solution near pH 7.

Is there a way to explain the practical issues clearly, but in fairly simple, somewhat physical rather than purely mathematical terms?


texts: Stereochemical aspect of heating of cyclohexane-1,2-diol

texts:
Does stereochemistry play any role in the heating of Cyclohexane-1,2-diol?

If I remember correctly, different products are formed depending on whether the diol is cis or trans. (I think the products are cyclohexanone and cyclopentanecarbaldehyde). Please clarify this along with the reason why different products are formed depending on the stereochemistry.


texts:
$\ce{2Ca3(PO4)2 +6SiO2 +10C->6CaSiO3 +P4 +10CO}$

What is the maximum amount of P4 that can be produced from 1.0 kg of phosphorite if the phosphorite sample is 75% $\ce{2Ca3(PO4)2}$ by mass

The wording is confusing. I do not know what to do. Would you start by finding the limiting reactant?


texts:
I have a question regarding synthetics. $\ce{(C8H8)}_n$ is the formula for polystyrene. What exactly does the $n$ stand for?

Thanks


texts: Is the kinetic energy change of a system (q) equal to the enthalpy change of a system (∆H)?

texts:
When silver nitrate and hydrochloric acid are put together in a container, they form silver chloride. If you're given information about the reactants (including temperature change, heat capacity, and mass of reactant aqueous molecules), then you can find the kinetic energy change of the system.

What I want to know is: does the $q$ value you find for the system equal to the $\Delta H$ value for the system? Worded differently, does the kinetic energy change of the system equal to the enthalpy change of the system? Is this one of those obvious questions that most people understand instantly but people like me who lack common sense don't?


texts: Are there any sources for tabulated Rf-values, especially 1-phenylazo-2-naphthol?

texts:
I  have synthesized 1-phenylazo-2-naphthol in my laboratory tutorial and have to analyze it. I've done a thin layer chromatography (TLC) of it:

solvent: ethanol
eluent: toluene
stationary phase: silica gel plate

My only problem is, I need an theoretical value for comparison but haven't found any source.


texts: How can I balance the following equation atomically and electrically?

texts:
$$\ce{C2O4^2- + MnO2 -> Mn^2+ + CO2}$$

I think that the half reactions are

$$\ce{C2O4^2- -> CO2}$$
$$\ce{MnO2 -> Mn^2+}$$

I am supposed to balance these by adding water, $\ce{H+}$ atoms and by adding $\ce{e-}$’s, but I’m just not sure on the method to do this as we’ve covered it extremely quickly.

First, I found the oxidation numbers for the overall equation, and I think that $\ce{C2O4^2-}$ is the reducing agent because $\ce{C}$ is losing charge from +3 to +4, I just don’t know how to use that to balance this. Any help would be appreciated.


texts: I'm in my high school's theatre crew and of course we build a lot of props and such. However I just opened (yesterday) an old drawer of screwdrivers and they smelled like puke! I know that the chemical responsible for that smell is butyric acid, so the rubber must have been a butyl rubber. Could someone point out the chemical equation that shows the reaction for this?


texts: $j$-$j$ coupling interaction in Magnetic Resonance Spectroscopy

texts:
I am studying Magnetic Resonance Spectroscopy and I have some difficulties in understanding the j-j coupling interaction. What does actually happen from the physical point of view to the electronic cloud of the neighbouring atom? When I try to understand in books like A Complete Introduction to MODERN NMR Spctroscopy of Roger S. Macomber (but also in websites) it seems to me that there are explainations more focused on quantum theory and its rules, but what I want to know is simply what happens physically at the electronic cloud and the consequent interactions ? Therefore why does this causes that in the spectrum, for example, of the Ethanol molecule (CH3CH2OH) there are three peaks related to -CH3 group? Or why in the Acetaldehyde molecule (CH3COH) there are four peaks related to -COH group and two peaks related to -CH3 group just for the j-j coupling interaction?
I really would like to see things clearer at the basis (so what happens physically to the electronic cloud and the consequent interactions) and thus being able to understand the number of peaks (while I think I have understood the chemical-shift interaction. I want also to specify that for the moment I have to consider just these two interactions because I am considering MRS applied to brain tissues which I can approximate as liquid so, for example, the dipolar interaction is considered average to 0).


texts: why is delocalization less effective when there is a separation of charge?

texts: I've been reading Peter Syke's book "A guidebook to mechanisms in organic chemistry" wherein he has frequently mentioned that delocatlization is less effective when there is a seperation of charge i.e instead of a double bond formation and a negative charge, there is a positive and a negative charge occurance eg. Formate ion and Formic acid


texts: How do the atomic orbitals look like in reality?

texts: We all know about atomic orbitals and their 3D structure. But the structure in theoretical. What does these orbital really looks like


texts: Why does cooking oil lower the vapor pressure of water?

texts:
I added different amounts of oil to different containers with 50mL of water and weighted the containers. Then I heated the containers for 15 minutes in a water bath and weighted again. I noticed that the mass of each container was less as I added more oil to the mixture.

So how does oil increases the boiling point/decreases the vapor pressure of water?


texts: I saw that the book said that nitrogen cations must have four bonds and no lone pairs. I wasn't sure why you couldn't have a lone pair and 2 bonds.


texts: Kinetic Diameter: How to calculate it? Pressure influence?

texts:
Wikipedia states:

Kinetic diameter is a measure applied to atoms and molecules that expresses the likelihood that a molecule in a gas will collide with another molecule. It is an indication of the size of the molecule as a target.

And the following equation is given:

$$d^2 = \frac{1}{πln}$$
where,
$d$ is the kinetic diameter,
$r$ is the kinetic radius, $r = d/2$,
$l$ is the mean free path, and
$n$ is the number density of particles.

To me, this implies that the kinetic diameter can be altered by changing the number density of particles. Therefore, a change in pressure, volume, or concentration should would effect the kinetic diameter.
However, kinetic diameters are often discussed as if they were constants. Indeed, Wikipedia even gives a table of kinetic diameters for some common molecules.

Another definition of the kinetic diameter would be useful.

How is the kinetic diameter related to molecular structure? Can it be quantified as the distance between a pair of atoms?

If someone could also suggest a computational program to calculate the kinetic diameter of a molecule, that would also be of use.


texts: Mixing two buffers of the same concentration, but of different pH

texts:
Does anyone know how to approach this?

I have two buffers of the same weak acid of the same molarity but at different pH

Let's say the pH of one was 8 and one was 7, how do I go about getting a pH of 7.6?

Thanks in advance


texts: HSAB: alkyl halides & carbonyls LUMO energy flaw

texts:
Hard electrophiles have LUMO of higher energy than soft electrophiles. Alkyl halides are considered to be soft electrophiles while carbonyl compounds are considered to be hard electrophiles. The sigma antibonding C-X orbital of an alkyl halide is higher in energy than the pi antibonding C-O orbital of carbonyls which is in contradiction with the previous statement.

How is this paradox explained?


texts: Why aren't free radicals considered resonance forms?

texts:
In C, the answer states that electrons must come in pairs. And so C does not show resonance forms.

But here I read that if there is an unpaired electron, it is a free radical. Why can't free radicals be part of the resonance form?


texts: Is carbon dioxide soluble in petroleum ether, and why?

texts:
I googled it, and I'm finding some forum posts that say no, but no authoritative reference.
CO2 is somewhat soluble in water (1.7 g/L at 20°C) and I understand that it's mostly NOT because it forms carbonic acid: it's just dissolved CO2 molecules. Why wouldn't the same thing happen in petroleum ether?
Has anyone tried putting petroleum ether in a SodaStream device?


texts: Why is the melting point of $\ce{NaCl}$ more than that of $\ce{RbCl}$ ? Using Fajan's Rule of polarizing power, $\ce{RbCl}$ has more ionic character and thus should have a higher melting point.


texts: Calculating volume of gases in different conditions

texts:
Doctor Who has a secret laboratory on Venus where atmospheric pressure is $92$ times that of Earth and room temperature is $\pu{735 K}$. There, Doctor Who mixes $\pu{4.00 g}$ of $\ce{CaCO3}$ with $\pu{40.00 mL}$ of $\pu{1.00 M}$ $\ce{HCl}$. What volume of carbon dioxide gas at VSTP (Venusian Standard Temperature and Pressure) is produced?

I know that the chemical equation is

$$\ce{CaCO3 + 2HCl -> CaCl2 + H2O + CO2}$$

Since there are $\pu{0.04 mol}$ of $\ce{CaCO3}$ and $\pu{0.04 mol}$ of $\ce{HCl}$, $\ce{HCl}$ is the limiting reagent; thus, $\pu{0.02 mol}$ of $\ce{CO2}$ are produced.

This is equivalent to:

$$V_\ce{CO2} = \frac{nRT}{p} =\frac{0.02 \times 0.08205 \times 735}{92} = \pu{0.013 L}.$$

However, the answer key says $\pu{26.2 mL}$ of $\ce{CO2}$ is produced, which is double my answer. Where did I go wrong in my reasoning?


texts: Why does LiAlH4 reduce an amide to an amine, but only reduce a ketone/aldehyde to an alcohol?

texts:
Here are two different reactions in which lithium aluminium hydride, $\ce{LiAlH4}$, reduces a carbonyl group:

Why does $\ce{LiAlH4}$ completely remove the oxygen from the amide, but only reduces the carbonyl group of a ketone/aldehyde to a hydroxyl group?  Is the difference due to the fact that $\ce{H2O}$ is added in the first reaction (i.e. if the aldehyde/ketone reduction had a second step where water was added, would the carbonyl group be reduced to a methylene group)?


texts: Is there an analytical chemistry alternative to the Scoville scale for the hotness of chilli?

texts:
The traditional way of measuring the perceived heat of a chilli is the Scoville scale which involves panel testing of diluted extracts taken from chilli. But panels are very variable and the results appear to be a little unreliable.

But we know the class of chemicals that creates the sensation of heat: capsaicinoids. Can't we just measure those directly?

Is there a better analytical method for measuring the heat of a chilli?


texts: Ordinary differential equation for molecule collision

texts:
I have no background in chemistry.

But, I have a good background in mathematics and computer programming.

I have planned to simulate the collision of two simple molecules $\ce{Br2}$ and $\ce{H2}$ just for fun and using state space and Ordinary Differential Equation (ODE) to simulate.

I have considered 24 states for simulations of their collision. The state vector is X, and the state space representation is:

X'=f(X,t)

Atom numbering

1: Br
2: Br
3: H
4: H

The 24 states for vector X are:

x1, x2, x3:  position of atom 1 in x, y, z axis
x4, x5, x6:  position of atom 2 in x, y, z axis
x7, x8, x9:  position of atom 3 in x, y, z axis
x10,x11,x12: position of atom 4 in x, y, z axis
x13,x14,x15: velocity of atom 1 in x, y, z axis
x16,x17,x18: velocity of atom 2 in x, y, z axis
x19,x20,x21: velocity of atom 3 in x, y, z axis
x22,x23,x24: velocity of atom 4 in x, y, z axis

To make a simulation, I need to know two things:

Are the mentioned states enough to describe the entire system?  Are there more states to be added?
What are the forces applied to each atom at each moment?

$\frac{d x_1}{d t}=x4$ (derivative of position is velocity)

$\frac{d x_4}{d t}=\frac1{m_{Br}}(???????)$ (derivative of velocity is acceleration)


texts: Is entropy of surroundings a state function?

texts:
It is a pretty common well known fact that the entropy of a system is a state function ie. it doesn't depend upon the path taken by the process as long as the initial and final states are the same.
I have a doubt whether we can say the same for surroundings or even the universe.
My first thought is that the entropy of the universe would be continuously increasing or at best it would be constant. It can never decrease. Thus the universe can never be at a state where it was before. The talk of state function seems strange here.
Still I am not very sure and I have no idea whether entropy of surroundings is a state function or not.
Any help would be appreciated.
Thanks


texts: Why is lead (IV) chloride covalent while lead (II) chloride ionic?

texts:
I would like to find out more about what makes a compound ionic and what makes one covalent. However, I felt this was too general a question so I thought that asking about the chlorides of lead would be more appropriate. I have already come up with an explanation of my own, which I have provided below. However, I would also like to hear the opinions of others.

My explanation is as follows: I consider the interaction between the atomic orbitals of the lead (II) and lead (IV) cations with the chloride ions. Firstly, we must note that their valence electronic configurations are different: lead(II) has its valence electrons in 6s orbital while the valence electrons of lead (IV) reside in the 5d orbital. On the other hand, the valence electrons of the chloride ions reside in the 3p orbital. Based on what I have read from Clayden's Organic Chemistry, I understand that atomic orbitals of similar energy interact strongly to produce strong covalent bonds. I was thinking that since the interacting orbitals of the lead (IV) cation and the chloride ions are closer in energy, a favourable covalent interaction would occur. However, in the case of lead (II), covalent bond formation is not favoured since the orbital energies are considered to be too far apart. I am not confident that this is correct. Please feel free to point out any inaccuracies.


texts: Solubility of silver acetate in the presence of nitric acid

texts:
What will be the effect on the solubility of $0.1\ \mathrm{mol}$ of $\ce{CH3COOAg}$ in presence of $1\ \mathrm{l}$ of $0.1~\mathrm{M}\ \ce{HNO3}$ solution?

  $$K_\mathrm{sp} (\ce{CH3COOAg}) = 10^{-8}\\
K_\mathrm{a} (\ce{CH3COOH}) = 10^{-5}$$

I know that silver acetate will react with nitric acid to form silver nitrate and acetic acid. So the solubility of $\ce{CH3COOAg}$ will increase. But in the end, I am not able to find out the final solubility (as concentration of $\ce{H+}$ and $\ce{NO3-}$ is coming different).

Maybe I have an error somewhere?


texts: pH Difference Our Taste Buds Can Recognise

texts:
Water at $50~^\circ\mathrm{C}$ has a $\mathrm{pH}$ of $6.63$, while the pH of water at $0~^\circ\mathrm{C}$ is $7.47$.

The temperatures are comparable to a chilled, iced drink (at $0~^\circ\mathrm{C}$) and a hot drink (at $50~^\circ\mathrm{C}$). Would these differences in acidity be noticeable? Would they be noticeable if the drink was more acidic, such as orange juice?


texts:
I might have a bit of a conceptual misunderstanding here, but how do we account for the entropy of a system when constructing a Hamiltonian? All entropy should be accounted, because the Hamiltonian includes the total energy, including the entropic contribution. However, when considering e.g. $\ce{H2+}$, the fact that the dissociated state is more entropically favoured doesn't go from the Hamiltonian.

Any suggestion that would clean up my understanding of the relationship between entropy and energy in this and other cases would be very helpful. Thanks!


texts: Does the prefix of an inverted unit also get inverted?

texts:
What is the energy of radiation that has a frequency of $\pu{2.51 \times 10^11 ms-1}$?
(a) $\pu{1.66 \times 10^-19 J}$ (supposedly correct)
(b) $\pu{1.66 \times 10^-22 J}$
(c) $\pu{7.92 \times 10^-37 J}$
(d) $\pu{1.66 \times 10^-25 J}$

My argument was that: since $\pu{Hz} = \pu{s-1}$, then $\pu{ms-1} = \pu{mHz}$. So, I divided $2.51 \times 10^{11}$ by $1000$ and solved the question normally (using $E = h\nu$). But my professor said that since $\pu{m}$ is a prefix, it should follow whatever is in front of it, so $\pu{ms-1}$ will become $1/\pu{ms}$, then you multiply it by 1000 to change it to Hz. Is that the correct way to do it?


texts:
CaCO3 (s) = CaO (s) + CO2 (g)

We know that pure solids quantity doesn't affect the position of equilibrium. But the application of pressure in gas does.

If we add CaCO3 in the closed system, the position of equilibrium should change, shouldn't it?

If we add CaCO3 the concentration shouldn't increase but the pressure in closed system should increase. Then it should affect in CO2 because the pressure has been increased.

Then why this is told that that pure solids quantity doesn't affect the position of equilibrium?


texts: How does binding energy "manifest" itself?

texts:
The concept of binding energy is, that it is equal to the energy that is needed to separate atoms in a covalent bond. I think I have understood that. The electrostatic powers between the atoms create a bond which needs to be "broken" to free the atoms.

My question is: If for example an exothermic covalent bond is created how does this bond energy get transferred to the surroundings? Atoms witch want to fulfill the octet rule create an electrostatic bond. HOW/WHERE is energy released and where did it come from?


texts: N-Hydroxysuccinimide (NHS) chemistry is commonly used in chemical biology to react with primary amines like lysine and the N-terminus of proteins. I was curious how labile NHS esters are to other nucleophiles like secondary amines and sulfhydryls. This knowledge will be helpful to know the extent of side products when I do a bioconjugation experiment.


texts: electron - nuclei recombination within stars

texts:
Nuclear fusion within stars combine atom nuclei, so the atoms are ionized and electrons run for free.
My question is, when or how these electrons recombine with the nuclei to form neutral atoms? inside the star? outside?


texts: The effect of temperature on the caffeine intensity

texts:
Does the brewing temperature have an effect on the caffeine level?
For instance, coffee with 100*C have higher caffeine level compared to coffee with 50*C?


texts: What is the difference between physical and chemical bonds?

texts:
If you characterize the chemical bonds to two categories physical and chemical bonds, how do you do it? Aren't all bonds chemical and physical?

From the freedictionary.com, chemical bond:

  Any of several forces, especially the ionic bond, covalent bond, and metallic bond, by which atoms or ions are bound in a molecule or crystal.

What is the physical bond then? How should the atom be bonded to molecule if these bonds are not the ones. What are these "several forces" excactly?

In the answer I would like to see the lists of chemical and physical bonds.


texts: Gauche conformations for 14-electron AH2BH2 systems

texts:
The hydrazine molecule, and the similar sulfonium/Oxonium ylides, all have a gauche conformation that is more stable than the anti conformation.

Is there any particular reason for this pattern? Orbital Interactions in Chemistry tries to use overlap between the 2 “lone pair” orbitals on the carbons as a justification (since it’s a 2 center 4-electron interaction).


texts: Am I visualizing/understanding atomic form factor correctly?

texts:
I'm having difficulty visualizing the concept of atomic form factor or atomic scattering factor as it has been presented in a chemistry course on X-ray crystallography that I'm taking. At the moment, I visualize it as such:

(Please note that the question marks in the diagram above are included to communicate my confusion.)
Am I visualizing this correctly? Is there any other way for me to interpret these diagrams? The course doesn't dive into the mathematics of atomic form factor (and neither does our accompanying text), so I don't have much to go on in developing a mental image of the phenomenon at play here--and I strongly suspect that the mental image that I do have is wrong since I can't find any evidence to support it.


texts: Vapour pressure and Boltzmann energy distribution

texts:
As theory says, there is always a certain amount of molecules in a liquid sample which have energies greater than a thresold energy and get free from intermolecular forces in liquid and produces the vapour. Theory also says that the temperature dependence of the vapor pressure is described by the following equation:
$$p = p^\circ \times \exp(-Q_\text{vap}/(RT))$$
But my question is how does this equation give such a specific value of vapour pressure while there are many molecules in the vapour phase having different ranges of energy, corresponding to different pressure ranges according to Boltzmann distribution law?


texts: How would you examine samples of rocks using a handheld spectrometer?

texts:
My friend has an old spectrometer set that his father used to own and we are trying to figure out how to use it. Asking his father about it is not an option unfortunately.
The box contains a handheld spectrometer. It is cylindrical in shape, length around 10 cm and diameter around 1 cm. There is a lens at both ends. We can't see through it.
In the box there are around 10 samples of different rocks. They are around the size of a golf ball but irregular in shape.
There is nothing else in the box. We presume there are components missing.
Is there some way to analyse these rocks with the spectroscope ?
Maybe I need to shine a laser or light on the rocks in some particular way, or grind a sample of the rock into dust and put it through a flame.
All suggestions welcome.


texts: Reaction of Tollen's reagent with 7‐oxabicyclo[2.2.1]heptan‐1‐ol

texts:
Identify whether the given compound will get oxidised by Tollen's reagent.

The problem here is with the bridged alpha carbon. It cannot pertain sp2 character in the middle of the reaction as it is not permittable according to Bredt's rule.


texts: If d-electrons are such poor shielders, why do trends increase more gradually across the d-block than the s or p-block?

texts:
If I understand correctly, the shielding effect of d- (and f-) electrons seems to be much poorer than those of s- and p-electrons, due to the fact that they are less penetrating, have less electron density near the nucleus and so on (as can be seen from radial distribution functions).

However, trends for ionization energy, electron affinity, and electronegativity are MUCH more gradual than for s and p-blocks. This means that the effective nuclear charge ALSO increases much more gradually in the d-block, as confirmed by Slater and Clementi values. If d-electrons were poor shielders, surely this would mean that Z-eff would be much higher?

Doesn't this mean that, say for period 4, 3d-electrons are much more effective at shielding the 4s-electrons, than the 4s-electrons are at shielding 4p-electrons? Why does this happen?

Is there another factor at play? Is it because we are adding electrons to an "inner shell" that the shielding becomes more effective? Is Z-eff = Z - S an incorrect guideline to use?


texts: If I mix a $\pu{2 M}$ solution with a different $\pu{1 M}$ solution, do the individual solutions reduce in molarity to $\pu{1.33 M}$ and $\ce{0.33 M}$ respectively?


texts: Relationship between Quantum Numbers and the Wave-function

texts:
I recently started learning about quantum mechanics and its applciations in atomic structure in chemistry.
In this inorganic textbook Inorganic Chemistry, it describes
"Each of the wavefunctions obtained by solving the Schrödinger equation for a hydrogenic
atom is uniquely labelled by a set of three integers called quantum numbers."
What is the relationship between the quantum numbers and the wave function? If the above is saying that each wavefunction is uniquely labelled by 3 quantum numbers, then it sounds to me that the 3 quantum numbers can describe the wavefunction on their own. But how can just 3 numbers describe a function?
On this website, it says the following
"A complete solution to the Schrödinger equation, both the three-dimensional wavefunction and energy, includes a set of three quantum numbers ( n,l,ml )."
Is the complete solution to the Schrodinger's Equation the wavefunction in 3D? what is the "energy" mentioned in the last quote to do with solution of the equation?
Thank you.


texts: How can I derive the preferred oxidation states of a transition metal from its electronic configuration?

texts: For example $\ce{Fe}\ (Z=26)$ Short formula: $\mathrm{1s^2\ 2s^2p^6\ 3s^2p^6d^6\ 4s^2}$. If we make the electronic formula we get 4 single electrons ($s=1/2$), which means that the valence in normal state is 4, but in the periodic table it is $2/3/6$. How can I find its valence?


texts:
In my lecture notes it was stated that in $\ce{Me3SiCH2SMe}$, deprotonation with tBuLi generates an anion in between Si and S. I've been not able to find the $\mathrm pK_\mathrm a$ values (not listed in Reich nor Evans).

Since Si is electropositive it should actively destabilise the anion, meaning that I'd expect to see terminal methyl group deprotonated.

No additional detail about conditions was given, but since it was tBuLi I presume low temperature (kinetic deprotonation).

Is there a reason why this deprotonation takes place? Are the $\mathrm pK_\mathrm a$ values relatively different?


texts: What is an example of a biodegradable polyethylene?

texts:
I would like an example of a Biodegradable Polyethylene.
I am using polylactic acid (PLA) as an example of a biopolymer/ bioplastic but I can not find a biodegradable polyethylene, that is a substance that contains polyethylene but has additives added so it biodegrades quicker


texts:
Water has a higher boiling point (100°C) than cyclohexane (81°C). This is probably because of stronger intermolecular forces between water molecules as compared to cyclohexane molecules. Then, why is the freezing point of cyclohexane higher than that of water? By the previous logic, water should be having a higher freezing point as well.

This is one among many examples. I am pretty sure than boiling point depends primarily on intermolecular forces while freezing point depends on both intermolecular forces and packing efficiency in the solid state. I am sure that both factors support a higher freezing point for water. So, what other factors govern the freezing point of a liquid substance?


texts: Does freezing a solution with water always cause the water to separate and form the ice lattice?

texts:
I'm curious, I was trying to look into the affect of freezing a solution with water even when the solution is completely miscible. I came across something that detailed this regarding salt water and basically said when it gets low enough to freeze, the water forms it's tell-tale lattice basically pushing the salts out so the ice itself is pure water and less dense (considerably less dense because the salt solution allowed the density to increase all the way to the lowered freezing point).

I am curious, is this a general fact of the behaviour of any solution with water regardless of miscibility? Are there water solutions which break up the lattice while still allowing freezing, or does the affect of blocking the formation of that lattice completely block the solution from freezing altogether no matter what? Are there water solutions which will freeze solid even with the lattice without just separating the non-water compounds?

Note: I recognize amorphous ice can be created with wizardry, but my question is more in regards to the typical behaviour on earth.


texts: Can we make glass by heating Martian Soil

texts:
I was puzzled by a very interesting question. Can we heat up Martian soil and produce glass just the way we do here on Earth? (the basic way)

For info, Martian sand consists of the following -

$\ce{Na2O}$ — $4~\%$
$\ce{MgO}$   — $14~\%$
$\ce{Al2O3}$  — $18~\%$
$\ce{SiO2}$   — $8~\%$
$\ce{P2O5}$  — $2~\%$
$\ce{SO3}$   — $10~\%$
$\ce{Cl}$ — $2~\%$
$\ce{K2O}$  — $2~\%$
$\ce{CaO}$  — $14~\%$
$\ce{TiO2}$   — $2~\%$
$\ce{Cr2O3}$  — $2~\%$
$\ce{MnO}$    — $2~\%$
$\ce{FeO}$ — $4~\%$
$\ce{Ni}$   — $8~\%$
$\ce{Zn}$    — $6~\%$
$\ce{Br}$    — $2~\%$

I can't see anything out of place here, if we heat it up, the silica
should do it at around $1700~\mathrm{^\circ C}$.

If we can figure out ways to make glass up there then it would be easy for Martian colonization if that is ever going to happen.


texts: Wavenumber range reversed in IR spectroscopy

texts:
I recently stumbled upon a result table from an IR spectroscopy, that is an image full of peaks. The goal was to decide which peak belongs to which group by looking up the intervals in a related table.

While the task itself is pretty straightforward, I can't explain to myself why the axis, as well as the intervals in the table, are "reversed" - meaning the higher values are on the left and the lower are on the right. In my opinion, this makes it much harder to quickly estimate if the given peak is in an interval or not:

e.g. for a number 2053, compare those two sets of intervals:

2100 - 2000
2070 - 2010
2050 - 2030

vs

2000 - 2100
2010 - 2070
2030 - 2050

The estimation seems to be easier with the second, at least for me.

Can someone provide a background on why the ordering is high-to-low and not low-to-high?

NOTE: I don't have any real background in the topic and so my view is rather naive.


texts: Do colligative properties depend on the number of solute molecules?

texts:
Colligative properties are properties that are affected by the number of solute molecules dissolved in the solution. True or false?

I think the statement is false, and the correct one should use "number of solute particles". I asked my TA and he said the molecule version is true, although I show him an example that $\ce{H2CO3}$ can dissolve water in many ways to create different sets of miles for $(\ce{CO3^2-},$ $\ce{HCO3-},$ $\ce{H+}).$ In this case, one mole of molecules $(\ce{H2CO3})$ can result in different total numbers of particles.

However, my TA said that $\ce{CO3^2-},$ $\ce{HCO3-},$ and $\ce{H+}$ can be considered as different molecules. I still don't satisfy with his answer though.

Could someone explain it for me, whether I am right or wrong.


texts: Intermolecular interaction between aniline and dichloromethane

texts:
Short background

As it is known there are interactions between:

Charges
Charge and dipole
Hydrogen bonding
van der Waals (VDW) forces

From stronger (1) to weaker (4).

VDW forces are divided into dipole-dipole, dipole-induced dipole, induced-induced dipole; also from stronger to weaker.

The problem

Reading about solutions I found interesting the intermolecular forces involved on aniline and dichloromethane mixing. Below both structrures are shown:

Aniline
 Dichloromethane

Question

What is the most important intermolecular force between those molecules and why? It might be interesting to see an AIM analysis of aniline, but I have no idea how to do that. Also, I'm not sure about what experiment could give valuable information on this case.

My attempt

Those previous interactions aren't mutually exclusive. $\ce{-NH2}$ might be a negative density region of the molecule (inductive attraction), but it is also donor by resonance, so the ring has partially a negative charge density. In consecuence, it is not easy to see the dipole. Dichloromethane, on the contrary, is an easy-to-see dipole.

It might result that London dispersion is the most relevant interaction here, but I can't very well justify it.


texts: What exactly does setting the net charge in a DFT calculation do?

texts:
In the implementations of DFT using Gaussian basis sets, it is common to set the net charge. What exactly does this do? The Gaussian (program) manual, for instance, says that it introduces a background charge distribution made of point particles. This raises more questions than it answers for me.

1) If it's made of point particles (presumably at some internally defined coordinates), how is it a background charge distribution?

2) What exactly does setting the charge do? Is it just adjusting the electronic energy? Does it impact the geometry optimizations or the spin states given a pre-specified spin multiplciity?

I'm having trouble understanding what the charge is actually doing in terms of the DFT calculation itself. It's not a setting in plane-wave calculations, so the parallels are not clear to me.


texts: Why does the amount of CO2 produced decrease with more baking soda?

texts: I'm in chemistry class and we have an assignment and they gave us a video and I took down the data they gave us. They fist measured out 10mL of vinegar for each trial and used different amounts of baking soda in all 8 trials. They put the baking soda in a beaker then poured the vinegar into the beaker and capped it with a one hole stopper and a syringe in the hole. It was about a 1-1.5 second delay between poring the vinegar and capping it. I don't understand why the amount of CO2 produced wouldn't increase at the beginning then flat-line when the vinegar becomes the limiting reactant. I posted a graph of the data we received. All trials had the same amount of vinegar.


texts:
We are home schooling my son, and right now we are covering chemistry- ionic bonds, covalent bonds, etc.  We've talked about how carbon is "special" in that it can form very complex molecules (organic chemistry), and I have done some hand waving by saying that it is its ability to make four bonds that causes that specialness.

He, quite reasonably, asked why nitrogen, with its ability to make three covalent bonds, couldn't be almost as special as carbon.  I told him that it probably can make pretty complicated molecules, but that only being able to make three bonds is a limiting factor.  That didn't seem to satisfy him, and to be honest, it doesn't totally satisfy me.

So why is carbon so special?  Is it just the four bonds vs. three, or is it something else?


texts: When alcohol is used to sterilize, what about it changes that it can't be re-used?

texts:
I read online that when you use regular household rubbing alcohol to soak something for sterilization purposes, you're then supposed to toss it out. I'm just curious why.

Like, as long as there's a lot of liquid still left, why is it not re-usable? Is it because there's bacteria or other stuff that transferred from whatever you were sterilizing into the alcohol, therefore reducing its effective % of alcohol, and that's what's important to sterilize, so once you're below a certain % concentration it's worthless. Or is it because the alcohol has actually evaporated off and what's left is just liquid (water)?


texts: What happens to a greenhouse gas after it absorbs infrared radiation?

texts: We say that a greenhouse gas increases the temperature of the surface of the earth but how does it do that ? Only by re emitting the absorbed IR towards the earth ?


texts:
What's the kinetic validity of the following way of balancing the above redox reaction?

I've done some searching of the literature; I've never come across oxide anions being mentioned in redox reaction mechanisms. Also, I read something about how two-electron reduction is impossible in a single step - something about spin pairing.

I'm fairly sure the following method is a good thermodynamic method of thinking about the reaction, but what about its kinetic validity?

I'm thinking that the below method isn't kinetically valid, but neither was it meant to be kinetically valid, and neither are the traditional methods of balancing redox reactions kinetically valid. Traditional methods call for balancing "O" and "H." But we aren't dealing with 0 oxidation state oxygens and hydrogens, are we?

Here is the thought process that my professor would take in solving this problem:

1) Skeleton reaction. Note that sulfur is being reduced from a +6 oxidation state to a +4 oxidation state. This suggests that the solid zinc loses two electrons.

$\ce{Zn + HSO4^- ->SO_2 +Zn^2+}$

2) Note that two negative two oxidation state oxygens are "disappearing" from left to right. In other words, what happened to the oxygens in the hydrogen sulfate ion?

$\ce{Zn + HSO4^- ->SO_2 +Zn^2+}$

$\ce{4~ negative ~two~ oxidation~ state ~oxygens -> 2 ~negative ~2~ oxidation~ state~ oxygens }$

3) The special thing about these oxygens is that they're negative two oxidation state oxygens. This suggests that these oxygens are the oxide anion. The oxide anion is highly basic in solution. Therefore, the oxide anions must have reacted with some system component, which caused them to "disappear." This would be the strongest acid in the system.

$\ce{HSO4^- ->SO_2 + 2O^2- (unstable)}$

$\ce{2O^2- + 4H3O^+ ->6H2O}$

4) Also note that a hydrogen proton disappears from left to right in the skeleton equation. Because the proton is highly acidic, it is attacked by the strongest base in the solution - water (since we're in an acidic solution).

$\ce{HSO4^- ->SO_2 + 2O^2- + H^+}$

$\ce{H^+ + H2O -> H3O^+}$

5) Final balanced equation:

$\ce{Zn + HSO4^- + 4H3O+ + H2O ->SO_2 +Zn^2+ +6H2O + H3O+}$


texts: $\ce{HBr}$ formation can be explained by simple orbital overlap as well as by $\mathrm{sp^3}$ hybridisation of $\ce{Br}.$ Can't we use dipole moment to find if the lone pairs on $\ce{Br}$ are mutually perpendicular or $\mathrm{sp^3}$-hybridised?


texts:
I work in a trace metals laboratory operating an ICP-OES. I've been having some trouble with the recovery of antimony in a weak $\ce{HCl}$ solution post-digestion.

The antimony is part of a mix of elements in ~$\ce{5\% HNO3}$, 1 mL of which is added to a beaker with ~$\pu{50 mL}$ of $\ce{0.5N HCl}$, then heated at a low temperature for ~10-15 minutes. There is a filtering process afterward using simple glass fibre filters. I've been getting between 60-75% recovery of the antimony, and at least 80-90% recovery of the other elements.

I've been able to find some information regarding issues with antimony and $\ce{HCl}$, and possibly with natural light affecting the stability of the solution, but nothing definitive or on-topic.

Any ideas?


texts: Determine Cu+2 and SO4-2 concentration using Potentiometry?

texts:
The title says it all. I've been researching as well but all I could come close was solid state ion selective electrodes. Could someone please help me out?

There should be two methods(or one) to measure the concentrations.


texts: Comparison of I-F, Br-F, and Cl-F bond strengths

texts:
From Chemistry of the Elements by Greenwood and Earnshaw [1, p. 833]:

  Figure 17.9 Mean bond energies of halogen fluorides.

This shows the mean bond energy for $\ce{X-F}$, where $\ce{X}$ is a halogen. I have several questions:

Why is the $\ce{X-F}$ bond in $\ce{XF}$ stronger than that in $\ce{XF3}$ or $\ce{XF5}$? I think it is because the $\ce{XF}$ bond has bond order 1, but $\ce{XF3}$ and $\ce{XF4}$ both have 3c-4e bonds. However, I am not too sure about this explanation. It also doesn't really explain why $\ce{XF5}$ is weaker than $\ce{XF3}$.
Why is the order of bond enthalpy generally $\ce{IF} > \ce{BrF} > \ce{ClF}$? I thought it would be the reverse, because smaller atoms would be able to have better atomic orbital overlap.

References

Greenwood, N. N.; Earnshaw, A. Chemistry of the Elements, 2nd ed.; Butterworth-Heinemann: Oxford; Boston, 1997. ISBN 978-0-7506-3365-9.


texts:
I wanted to know wether we can prepare aryl halides by Hundiecker reaction or not. if so then what is its mechanism i know the mechanism for alkyl halides. please refer these links and please try to explain with reason.

http://www.organic-chemistry.org/abstracts/literature/918.shtm

http://www.organic-chemistry.org/abstracts/literature/449.shtm


texts: Reference Request - bond lengths in PCl2F3

texts:
While writing an answer here, I needed references for bond lengths of $\ce{PF3Cl2}$ and $\ce{PF4Cl}$. The latter was easily found in reference (1), whereas I could not find exact references for bond lengths in the former molecule.

References (2) and (3) contain information about the Raman spectra and $\ce{F^{19}}$ NMR spectra, but do not contain information about bond lengths. Reference (2) has information about the bond lengths of $\ce{PCl3F2}$, $\ce{PF5}$ and $\ce{PCl5}$, but not for $\ce{PF3Cl2}$.
A reference for exact bond lengths in $\ce{PF3Cl2}$, similar to the bond lengths shown above, is appreciated.
References:

Leiding, J., Woon, D. E., & Dunning, T. H. (2013). "Bonding in $\ce{PF2Cl}$, $\ce{PF3Cl}$ and $\ce{PF4Cl}$: insight into isomerism and apicophilicity from ab initio calculations and the recoupled pair bonding model". Theoretical Chemistry Accounts, 133(2). doi:10.1007/s00214-013-1428-7
Griffiths, J. E., Carter, R. P., & Holmes, R. R. (1995). "Molecular Structures of $\ce{PCl4F}$, $\ce{PCl3F2}$, $\ce{PCl2F3}$, and $\ce{PF5}$: Infrared and low-temperature Raman Vibrational Spectra". Phosphorus, Sulfur, and Silicon and the Related Elements, 98(1-4), 11–31. doi:10.1080/10426509508036938
Holmes, R. R., Carter, R. P., & Peterson, G. E. (1964). "Molecular Structures of $\ce{PCl4F}$, $\ce{PCl3F2}$, and $\ce{PCl2F3}$: Pure Chlorine Nuclear Quadrupole Resonance and Low Temperature $\ce{F^{19}}$ Nuclear Magnetic Resonance Spectra". Inorganic Chemistry, 3(12), 1748–1754. doi:10.1021/ic50022a021


texts: The diference between covalent molecule lattice and covalent network lattice

texts:
Can you tell me the difference between covalent molecular lattice and covalent network lattice?
Thanks for your help.


texts: Are 1st Electron Affinities positive or negative?

texts:
According to this ChemistryLibretexts website and this StackExchange answer,  1st electron affinites are negative and 2nd electron affinities are positive.

However, according to this Study.com website, 1st electron affinity (energy released) is positive.

Both contradicting websites address the point that when electrons are added to a neutral atom, energy is released. But the only problem is that one website says that when this exothermic reaction occurs, the 1st electron affinity is negative, while the other states that the 1st electron affinity is positive. Which one is right?


texts: Is rotation/flip of skeletal structural formula of Sildenafil/Claim 6 okay?

texts:
I want to show visually the similarities between Sildenafil (Viagra) and the molecule on the right:

Is it allowed to flip the skeletal structural formula and rotate bond strings of the molecule on the right to better show the similarities like I did it in the following figure?

The molecule on the right is flipped at the horizontal line and the bottom left C$_2$H$_5$ is rotated outwards. In both cases, the structure is the same, but I stumbled on things like enatiomeres and optical isomerism, and now I'm confused. I red "Graphical representation standards for chemical structure diagrams (IUPAC Recommendations 2008)" partially, which seems to allow transformations like tried above, but as non-chemist, I'm still unsure.


texts:
I'm still working on my concepts related to chemical equilibrium. I came across this question:

10mL of a weak acid HA is 20%
dissociated in water. This solution is completely neutralised by 10 mL
of $10^{-3}$ M of NaOH.

Is [$\ce{HA}$] = $10^{-3}$ M or is [$\ce{H^+}$] =$10^{-3}$?
Why is it wrong to say that since NaOH completely dissociates, and solution is neutral, [$\ce{OH^-}$] =$10^{-3}$ M= [$\ce{H^+}$]?
Here, [.] denotes concentration.


texts: Consequence of interactions between filled orbitals

texts: It is known that the interaction between filled orbitals from the perspective of molecular orbital theory is overall destabilising because antibonding MOs are more antibonding than bonding MOs are bonding. Consider a large molecule (e.g. $\ce {I2}$). Due to the presence of multiple net destabilising interactions between the filled inner shell atomic orbitals (e.g. $\ce {1s, 2s, 2p}$ ...), wouldn't its formation be almost impossible since the single stabilising interaction due to the valence atomic orbitals would be small, compared with the total destabilisation from all the interactions between the inner shell orbitals, which are in fact, very numerous?


texts: How is the pKa of extremely weak acids determined?

texts:
According to Wikipedia, the conjugate acid of LDA has a pKa of about 35 - which is in line with figures I've seen elsewhere.

How then can such a weak acid's pKa be determined? If the determination is made in water, how is that even possible? Water would be a stronger acid by far and couldn't it easily mask the acidity of LDA's conjugate acid?

Is LDA's pKa value even determined in water?

Similarly, how are extremely strong acids' pKa values determined? Wouldn't the leveling effect come into play as one introduces, say, tosic acid into water? How then can we determine the strength of an acid stronger than hydronium ion in water?


texts: Thermodynamics- How are various property tables made?

texts: I've always been curious about how different thermodynamic property tables are made. It's really interesting to me. I want to know how different things such as critical properties and variations of properties of different substances are determined. I'm not familiar with statistical physics, but any derivations using it would be great for future reference.


texts: Are there two compound resins that tolerate over 1000°C for glass/carbon fiber?

texts:
I'm a hobby enthusiast that loves to play with electronics so my major is not in chemistry, there for I'm hoping that this forum is the right place to find aid in this question.

I've searched day in and day out, and when someone refers to "epoxy" with "extreme high temperature tolerance" they're generally speaking about 200-300°C, which to me isn't that much.

I can understand that depending on the context that is a lot, but there has to be something that is actually "extreme" in the sense that it can tolerate up to 1000 °C since formula 1 cars typically hit around 1000°C at the end of a break line and typically the thickness and heat dispersion of the setup just can't take more because of the limits within FIA.

So my question is, what is the technical term for high temperature epoxy's and what other options is there if not?


texts: What's the reaction mechanism for the oxidation of primary alcohols (e.g. ethanol) to carboxylic acids using acidified KMnO4?

texts:
I've seen mechanisms for $\ce{MnO4-}$ in base reacting with primary and secondary alcohols to oxidise them, but what about $\ce{MnO4-}$ in acid?

All the ones I've found have either been referring to $\ce{MnO4-}$ in base or just showed the redox reaction occurring. I've been trying to look for one for a while now, but I still haven't found a satisfying one (i.e. one that goes beyond showing the reaction in redox equation form).

I hope anyone who knows anything about it can answer me on that, and as thoroughly as you can. Thanks.


texts: Is it possible to use the laws of termodynamics for non-ideal systems?

texts:
For the reaction

$$\ce{2CO(g) + O2(g) -> 2CO2(g)}\quad\Delta H = \pu{−560 kJ}$$

it is given that the reaction occurs at constant volume of $\pu{1L}$ and the initial and final pressures are $\pu{70 atm}$ and $\pu{40 atm},$ respectively, with an initial temperature of $\pu{500 K}.$ It is further given that all the gases show significant deviation from ideal behaviour.

I don't understand how we can apply the standard equation of

$$\Delta H = \Delta U + \Delta n_gRT \quad\text{or}\quad \Delta H = \Delta U +\Delta(PV)$$

As compared to

$$\Delta H = \Delta U + z\Delta n_gRT \quad\text{or}\quad \Delta H = \Delta U +\Delta(PV)/z$$

However, the only solutions I found to this problem use the standard equations.


texts: Why does fusing benzene rings not produce polycyclic alkynes?

texts:
It would make sense that when the benzene rings are fused they keep their pi bonds and form a polycyclic alkyne. However this is not the case.

My hypothesis is that because monocyclic alkynes at 8C or above are stable polycyclic alkynes would be even more stable and more stable with smaller rings than monocyclic alkynes.

However with 7 benzene rings fused in a hexagonal tiling type fashion the center ring has all single bonds like cyclohexane.

Why is it that fusing benzene or really any aromatic compound does not form polycyclic alkynes?

A resonance structure of this would be a polycyclic alkyne along with just the regular pi bond delocalization.

Bicyclo[4.4.0]deca-1,3,6,8,tetraene-4-yne is what I am thinking about. I am moving just the pi bonds in the resonance structure to get this. I am not moving actual carbon nuclei.

I can't find a picture of this but hopefully from the name you can figure it out.


texts: E1 selection rules for transitions between two Σ states

texts:
For E1 selection rules (embodied in the electronic transition moment), to have an allowed transition the direct product of irreducible representations (IRs) must contain the totally symmetric IR. So, for transitions between two $\Sigma$ states, the following transitions are symmetry allowed: $\Sigma^- \leftrightarrow \Sigma^-$ and $\Sigma^+ \leftrightarrow \Sigma^+$.
But I read in Herzberg's book "Molecular Spectra and Molecular Structure I: Spectra of Diatomic Molecules" that in Hund's case b when we have a rotational distortion of the electronic motion or spin-orbit interaction, the $\Sigma^- \leftrightarrow \Sigma^+$  transition can appear.
Although for rotational distortion I understood that this violation is due to the $- \leftrightarrow +$ rule. I am wondering whether the direct product rule does not apply anymore?
Could you please tell me if there are other cases to consider where the $\Sigma^- \leftrightarrow \Sigma^+$ transition is allowed? And did I misunderstood the selection rule governing the transitions between two $\Sigma$ states?


texts: How does the Lennard-Jones potential relate to energy?

texts:
Considering the Lennard-Jones potential,

$$V(r)=\frac{A}{r^{12}} − \frac{B}{r^{6}}$$

How does this relate to force or energy? I suspect that there is some physics equation I'm forgetting. I know that $F=−\nabla(V)$, but that's a partial derivative with respect to time, and I don't see how time comes into effect here. Also, the derivative of energy (work) with respect to displacement is force, but I'm not sure how to connect that to potential.

An example application that stimulated this question: given the interaction potential above, how would you find the interaction energy between two systems?


texts: How to determine force constant of C-C bond in ethanol?

texts:
How would one determine the theoretical force constant of the C-C bond in ethanol?
We are asked to calculate the frequency of the C-C bond (theoretical), but to do this we need a force constant, which is not provided to us.
I cannot find a source of this information. The only way I see to calculate the force constant is from the frequency of the bond, which is what we are asked to calculate.
This professor has a reputation of omitting important details

Use the fundamental stretch function below to determine what is the frequency of the C-C bond and what is the wavenumber?
$$\bar{\nu}\mathrm{(cm^{-1})}=1303\sqrt{f\left(\frac{1}{m_1}+\frac{1}{m_2}\right)}$$
where $f$ is the force constant in N/cm, and $m_1$ and $m_2$ are the masses in atomic mass units (u). Compare your calculated values with the experimental value. Provide the reference.


texts: Cyanide hydrolysis; could it yield an oxime?

texts:
The mechanisms for both acid and base catalyzed hydrolysis of nitriles are clear;

(With the subsequent deprotonation from the hydroxyl) and

(Source)
In both cases, the hydroxyl adds to the carbon while the proton adds to the nitrogen.
I thought up an alternate mechanism, with the proton attaching to the carbon, and the hydroxyl going to the thereby positively-charged nitrogen, yielding an oxime.
Why doesn't this occur? I thought of the fact that the nitrogen atom, with a lone pair, would cause any nearby protons to come straight to it, but I'd like clarification on that.


texts: Primary carbocation in addition of HBr to ethylene?

texts:
All mechanisms of the addition of a halogen acid to ethylene (ethene) I can find involves a primary carbocation as the intermediate ion.

However, primary carbocations are generally unstable and unlikely to form. This can indeed explain why the first step is the rate-determining step, but does primary carbocations really form in the process? Is there no other plausible explanations?


texts:
An organic compound X of formula $\ce{C5H10O2}$ forms two compounds when boiled in aqueous sodium hydroxide solution. One of these compounds forms a ketone when treated with acidified potassium dichromate.

  Compound X could be

  \begin{array}{ll}
\textbf{A} \quad \ce{CH3COOCH(CH3)2}. \qquad & \textbf{C} \quad \ce{CH3CH2COOCH2CH3}. \\
\textbf{B} \quad \ce{CH3CH2CH2CH2COOH}. \qquad & \textbf{D} \quad \ce{(CH3)2CH2COOCH3}.
\end{array}

Can someone confirm that the correct answer is option A instead of C?

Since one of the compounds (alcohol) forms a ketone, therefore it must be secondary alcohol. This means the ester must be branched, so it would be A?


texts:
Is it possible to describe a reaction of the
$$\ce{A + B <=> AB}$$
exactly using the solution of an isomerization reaction?
$$\ce{A <=> B}$$

I just can not figure it out the equations seem so similar but the solution in my script is so convoluted that I can not prove they are equal.

Equations for top reaction:
$${\partial c_\ce{AB} \over \partial t} = -k_\mathrm{off} c_\ce{AB} + k_\mathrm{on} c_\ce{A} c_\ce{B}$$
and for the bottom:
\begin{align}
{\partial c_\ce{A} \over \partial t} &=
  -k_{\ce{A -> B}} c_\ce{A} + k_{\ce{B -> A}} c_\ce{B}\\
{\partial c_\ce{B} \over \partial t} &=
   k_{\ce{A -> B}} c_\ce{A} - k_{\ce{B -> A}} c_\ce{B}\\
\end{align}

Could we not just represent $\ce{A + B <=> AB}$ as a new reaction with $\ce{C $=$ A + B}$ and $\ce{D $=$ AB}$ and thus use the isomerization results on $\ce{C <=> D}$?

I could write a set of equations for the $ A+B \rightleftharpoons AB $ reaction :
$${\partial c_{AB} \over \partial t} = -k_{off} c_{AB} + k_{on} c_A c_B$$
$${\partial c_{A}c_{B} \over \partial t} = +k_{off} c_{AB} - k_{on} c_A c_B$$

which looks suspiciously like the $$A \rightleftharpoons B$$  reaction.

A starting point might to prove they can be used to express each other would be to use the equilibrium relation
$$k_d = { c_\ce{A} c_\ce{B} \over c_\ce{AB}}$$
with the relation for the total number of species A $c_\mathrm{total} = c_\ce{A} + c_\ce{AB}$ to get :
$$c_\ce{A} c_\ce{B} = k_d (c_\mathrm{total} -c_\ce{A})$$


texts: Use a solid or liquid stationary phase in gas chromatography

texts:
In my textbook, they mention that the stationary phase used in gas chromatography is a solid, such as silica or an adsorbed high-boiling-point liquid.

My question is that what is the advantage of each one, in what situation one will be better than the other, or if it matters at all.

Also, how does the stationary phase not get carried away with the mobile phase? since a high-pressure gas is used doesn't the stationary phase just get carried along with the mobile phase, especially if it is liquid?


texts: Which chemical reactions don't involve bond breaking?

texts: I recently came across a question in which an option is 'Breaking a chemical bond is the first step in any chemical reaction', which lead me to think of reactions which do not involve bond breaking. The only reaction I can think of is dimer formation, but a Google search reveals no more. Surely this cannot be the only example?


texts: Heat of combustion among substituted cyclohexanes

texts:
Arrange in ascending order of heat of combustion:

I know heat of combustion is inversely proportional to stability. Also, to solve I did try making chair conformations of the substituted cyclohexane.
In same type of, say, 1,3,5-conformations one can do comparisons by seeing equatorial axial positions, as bulky group tend to be in equatorial positions. But how to compare and arrange when there is 1,2,3 and 1,2,4 and 1,3,5 substitutions?


texts: Deriving the partition function for a harmonic oscillator

texts:
This question is in reference to an answer I posted here yesterday.

In it I derived the partition function for a harmonic oscillator as follows

$$q = \sum_{j}e^{-\frac{\epsilon_j}{kT}}$$

For the harmonic, oscillator $\epsilon_j = (\frac{1}{2}+j)\hbar \omega$ for $j \in \{ 0,1,2.. \}$

Note that $\epsilon_0 \neq 0$ there exists a zero point energy.

Let's write out a few terms $$q = e^{-\frac{\hbar \omega/2}{kT}} + e^{-\frac{\hbar \omega3/2}{kT}} + e^{-\frac{\hbar \omega5/2}{kT}} +..... $$

factoring out $e^{-\frac{\hbar \omega/2}{kT}}$

$$q = e^{-\frac{\hbar \omega/2}{kT}} \left( 1+ e^{-\frac{\hbar \omega}{kT}} + e^{-\frac{2\hbar \omega}{kT}} +.....\right) $$

The sum in the bracket takes the form of a geometric series whose sum converges as shown below $$1+x+x^2+... = \frac{1}{(1-x)} $$
 herein, $ x \equiv e^{-\frac{\hbar\omega}{kT}} $

Putting all of this together

$$q = \frac{e^{-\frac{\hbar \omega/2}{kT}}}{(1-e^{-\frac{\hbar\omega}{kT}})}$$

I happened to check Atkins Physical chemistry (10th edition) for the same derivation earlier today.

On page 620, the vibrational partition function using the harmonic oscillator approximation is given as
$$q = \frac{1}{1-e^{-\beta h c \nu'}}$$, $\beta$ is $\frac{1}{kT}$ and $\nu'$ is wave number

This result was derived in brief illustration 15B.1 on page 613 using a uniform ladder. However, in that illustration the uniform ladder starts at 0, but the harmonic oscillator has a zero point energy (which I accounted for in my derivation).

I discussed this with my instructor and he pointed out that as $T \rightarrow 0$ $q \rightarrow 1 $ (since only one state is thermally accessible.

The result derived in Atkins' does that indeed, but mine goes $q \rightarrow 0$.

Now, in the formalism developed in Atkins the do set the ground state energies to zero (on page 605), and basically add non-zero ground state energies to a calculated $\langle \epsilon \rangle$, which is fine.

Anyway, I would love it if someone could weigh in on this and help me resolve this conceptual mess in my head.


texts:
Why can we use $\ce{H+}$ and $\ce{H3O+}$ interchangeably?

I have seen in many places that first the reaction is written including Hydronium ion but then in bracket its written that we can write it as $\ce{H+}$ for simplicity. I am not clear with this.
$$\ce{H2O +H2O <=> H3O+ + OH-}$$
OR
$$\ce{H2O(l) <=> H+(aq) + OH- (aq)}$$


texts: Would concentration of a compound in equilibrium increase even if it's not favored by a volume decrease?

texts: So say I have a reaction where there are x moles of gas on the reactant side, and y moles of gas on the product side, where x>y. The volume decreases, favoring the products side. The textbook I am using says that the equilibrium concentration of the reactants would decrease, but wouldn't it end up increasing due to the lowered volume?


texts: Why does water attack the more substituted carbon in oxymercuration?

texts:
In hydration of an alkene by oxymercuration-demercuration, for an asymetrical mercunium ion, the more substituted carbon atom is attacked by water.

Why is this the case? Since R groups are electron donating, it should make the more substituted carbon less electrophilic, also water would like to attack the carbon having less steric hindrance but the reverse is true.


texts: Why doesn't sulfate get electrolyzed in sulfuric acid electrolysis?

texts:
If I have aqueous sulfuric acid solution as electrolyte and the anode electrode is made out of copper and the cathode electrode is made out of graphite, what are the two reactions at the respective electrodes and why?

\begin{align}
\text{Anode:}  && \ce{Cu &-> Cu^2+ + 2e-}\\
\text{Cathode:}&& \ce{2e- + 2H+ &-> H2 (g)}\\\hline
\text{Total:}  && \ce{2H+ + Cu &-> H2 + Cu^2+}
\end{align}

That should be the reaction, but why? Why isn't sulfuric acid participating? Why does that specific reaction happen?


texts: Nucleophilic Aromatic Substitution in ring with 4 Substituents

texts:
Does the chlorine still get substituted by OH in this case?

I was also wondering, if it does get substituted, does anything happen between the ethanol substituent and the phenol -OH? I'm suspecting that there might be some kind of ring formation...just a strange feeling.

Thanks!


texts: Is there any library functions which I could use in python to construct slater determinant? Can someone suggest me something to fix this issue ? Is it really possible to determinant with functions as elements of the determinant ?


texts:
I came across an ionic equilibrium problem stating:

  Find the pH when 150 ml 1 M $\ce{NaOH}$ has been added to 100 ml 1 M $\ce{H3PO4}$.

I'm stuck with this question. What I know:
$$\ce{H3PO4 + NaOH -> NaH2PO4 + H2O}$$
$$\ce{NaH2PO4 + NaOH -> Na2HPO4 + H2O}$$

Finally 50 millimoles $\ce{Na2HPO4}$ and 50 millimoles $\ce{NaH2PO4}$ remains.
Should I apply acid buffer equation?


texts: Why is the concentration halved at the intersection of Hg²⁺/Hg₂²⁺?

texts:
For the couple $\ce{Hg^2+}/\ce{Hg2^2+}$: $E^\circ = \pu{0.91V}$.
  At the border the concentration is $c = \pu{0.10 mol \cdot L-1}$ for all ions. Hence build the stability diagram of mercury.

I have:
$$\ce{2Hg^2+ +2e- <=> Hg2^2+}$$

Then by the Nernst relation I have:
$$E = E^\circ + \pu{0.03 V} \times \log\left( \frac{\left[\ce{Hg^2+}\right]^2}{\left[\ce{Hg2^2+}\right]} \right)$$

In the solution of the exercise they write:

  At the border $\left[\ce{Hg^2+}\right] = \left[\ce{Hg2^2+}\right] = \frac{c}{2}$.

I don't understand why it is $\frac{c}{2}$.


texts: Determining geometry of trisubstituted alkene

texts:
The way I know to tell whether an alkene is E or Z -is to look at the coupling constant of the protons across the doble bond. Large value (16 Hz) indicates an (E)-alkene where as smaller values (11 Hz) usually indicate a (Z)-alkene.

In my project I've been doing a cross metathesis between two alkenes which gives me a tri-substituted alkene, and I cannot observe the coupling constant across this double bond. The reaction gives a mixture of products which I think are the (E)- and (Z)-isomers. I'm able to separate them on HPLC but they do not crystallise.

Is there another method of determining this? A lab member suggested I could derivatise the alkene but I don't think this would provide any more useful information.


texts: Clarification on Oxidation Number and Ionic Charge

texts:
I am confused on the differentiation between ionic charge and oxidation number (state).  For example and simplicity, $\ce{NaCl}$ is an ionic compound so it forms $\ce{Na+}$ and $\ce{Cl-}$.  Are these ($1+$ for $\ce{Na}$ and $1-$ for $\ce{Cl}$) both the oxidation states and the ionic charges?  Or is the net of the compound ($\ce{NaCl}$) the ionic charge?

Additionally, when you have something such as $\ce{C2O4^2-}$ in this case a covalent compound , carbon's is $3+$.  Is this carbon's oxidation state?  What then is the net charge of the compound ($2-$) called?


texts:
In metallurgy, an ore is defined as that mineral from which metal can be obtained with economic viability.
I have also read that ores are rocks from which minerals or metals can be extracted profitably.
 If ores are rocks they cannot be minerals as rocks are aggregates of mineral and vice versa, so which of these is actually correct?


texts: is there a lead compound that crosses the blood-brain barrier when ingested?

texts: for example mercury oxide has neurotoxic properties but isn't organic so, it isn't soluble in lipids and so doesn't cross the blood brain barrier when ingested, however, methylmercury chloride is organic and soluble in lipids thus it can cross the blood brain barrier


texts: Why thermodynamic state variables of a sytem are only defined at thermodynamic equilibrium and not during any other instant?

texts: As you have read the title so my question is why are thermodynamic variables only meaningful when the thermodynamic system is in thermodynamic equilibrium and is always meaningless in any other case.


texts: Why do crown ether look the way they do?

texts: Like, the structure of lines of the rings of crown ether looks very different from regular cycloalkane rings. For example, the oxygen in crown ether is pulled more inside the ring. The line between carbon atoms consecutively bonded look almost horizontal. Why?