texts: Calculating entropy: why consider a reversible path?

texts:
I am reading up on entropy in a textbook and I got confused by this:

It says that to calculate the entropy for an irreversible process using heat flow, one must imagine the reversible process in which the initial and final states are the same as for the irreversible process. Why is this so and why do we need to think of it in the reversible way?


texts: Finding initial pressure in a chemical equilibrium

texts:
Consider the equilibrium below. If $K = 4$ and initial pressures of $\ce{CO}$ and $\ce{H2O}$ are equal, giving a total pressure of $1.5~\mathrm{bar}$ at equilibrium. What was the initial pressure of $\ce{CO}$ or $\ce{H2O}$?

$$\ce{CO(g) + H2O (g) <=> CO2 (g) + H2 (g)}$$

I don't know how to get the initial pressures in this situation. Do I have to set up an ICE chart? I'm not sure how to start, any help would be appreciated. The answer is apparently $0.75~\mathrm{bar}$.


texts: Why are 'table salt and sugar are both terrible candidates for recrystallization'?

texts:
I received a comment on one of my other chemistry questions stating that

  table salt and sugar are both terrible candidates for recrystallization, albeit for different reasons.

Why are salt and sugar terrible candidates for recrystallization?


texts: What happens to chemical bonds if the nucleus changes?

texts: Lets say I have some $\ce{PuF6}$ (with the Plutonium being $\ce{^{240}Pu}$). I take this $\ce{PuF6}$ and bombard it with neutrons. The $\ce{^{240}Pu}$ nuclei capture the neutrons, forming $\ce{^{241}Pu}$, which decays after some time to $\ce{^{241}Am}$. $\ce{AmF6}$ is not a stable molecule from what we know - we can't synthesize it in labs. So what exactly happens to the chemical bonds? $\ce{AmF4}$ seems stable - does a difluorine molecule just get "kicked" off?


texts: Online list of water of crystallisation?

texts:
I was extremely happy to recently receive a copy of the Nuffield Revised Book of Data but was somewhat disappointed to find that it did not list data on the water of crystallisation for various compounds.

Does anybody know of any large online tables or databases of reliable water-of-crystallisation data?


texts: Does chelation take ions out of solution

texts: Does EDTA take $\ce{Mg^{2+}}$ and $\ce{Mn^{2+}}$ out of solution, so that it can be removed by a filter? Or does it just take it out of any chemical reactions going on in the solution?


texts: Can we relate approximate Hartree-Fock orbitals to true solutions in the basis-set limit?

texts:
Assume that we've "solved" the RHF Hartree-Fock equations in some finite basis, that is, we have arrived at a self-consistent set of coefficients $c_{\mu{}i}$ such that each spatial molecular orbital is expanded as $\chi_i = \sum_{\mu=1}^K c_{\mu{}i}\varphi_i$. By construction, this set of orbitals is orthonormal, and forms a collection of eigenfunctions for the Fock operators in the given basis, so $f_i |\chi_i\rangle = \varepsilon_i |\chi_i\rangle$ where $\varepsilon_i$ is the $i$th orbital energy.
Question: what, if anything, can we say about these orbitals in terms of their relationship to the "true" orbitals in the basis set limit, denoted $\chi_i^\mathrm{BS}$? Here, I mean those orbitals that would be obtained if the calculation were to be extended to an (infinite) complete basis set. (I realise that the assumed existence of a single unique set of true orbitals may not be justified...)
For example, is it possible to estimate, bound, or otherwise describe the overlap $\langle \chi_i | \chi_i^\mathrm{BS} \rangle$ between an approximate solution and the true solution? How about matrix elements such as $\langle \chi_i | \mathcal{H} | \chi_i^\mathrm{BS} \rangle$, where $\mathcal{H}$ is the electronic Hamiltonian, or indeed any self-adjoint operator?
I suspect/hope that some kind of a statement towards the first part might be possible, given that the Roothan-Hall equations are effectively a collection of Galerkin equations. One of the standard hand-waving statements about solutions obtained using Galerkin methods is that they are in some sense projections of the true solution onto finite-dimensional subspaces, and have residual vectors that are "orthogonal" to that subspace(for a potentially complicated definition of "orthogonal").
(I'm also interested in answers that would apply in any of the HF settings, i.e. UHF, ROHF, etc.)


texts:
I was solving some questions on amines when I happened to see the below question:

  propan-1-amine + ($\ce{NaNO2 + HCl}$)= a mixture of products
  (originally, the mixture in brackets on the reactant side was just
  written as $\ce{HNO2}$)

  The mixture contains:

  a.    1-Propanol

  b.    2-Propanol

  c.    Cyclopropane

  d.    All of these

The answer happened to be "d. All of these". I could understand the formation of 1-propanol and 2-propanol but not cyclopropane. The answer given in the textbook wasn't clear and I couldn't understand. It said that the carbocation intermediate had something to do with it which I couldn't follow.

Can someone explain what is behind all this?


texts: Which are the major truths of paradigms on which the whole body of chemistry is built?

texts: For example, as evolutionary theory is fo biology or the existence of numbers for math, the existence of an independent reality for physics, etc.


texts: pH for an HA/NaA solution using a contour map

texts:
The following question has troubled me for a while now.

A virtual weak acid $\ce{HA}$ dissociates as follows:
$\ce{HA <=> H^+ + A^-}$
with the acid dissociation constant $K_\mathrm{a} = 10^{-3.00}$.
A solution is prepared using a given concentration of $\ce{HA}$, $C_\ce{HA}$ , and a given concentration of its conjugate base salt $\ce{NaA}$, $C_\ce{NaA}$. The pH of the solution depends on these concentrations. The dependence of the pH on $\mathrm{p}C_\ce{HA} (= −\log C_\ce{HA}$) and $\mathrm{p}C_\ce{NaA} (= −\log C_\ce{NaA}$) is
shown as a contour map below. A doubling in $C_\ce{HA}$ corresponds to a $–0.30$ shift of $\mathrm{p}C_\ce{HA}$ to the left in this contour map.

Figure 1. Contour map of pH for an $\ce{HA/NaA}$ solution.
In this case $C_\ce{NaA}$ is ideally zero and can be neglected. In the above contour map, this situation corresponds to either region $A$, $B$, or $C$, where $\mathrm{p}C_\ce{NaA}$ is large and the following inequalities for $\mathrm{p}C_\ce{HA}$ hold:
Region A: $\mathrm{p}C_\ce{HA} < \mathrm{p}K_\mathrm{a}$
Region B: $\mathrm{p}K_\mathrm{a} < \mathrm{p}C_\ce{HA} < \mathrm{p}K_\mathrm{w}/2$
Region C: $\mathrm{p}K_\mathrm{w}/2 < \mathrm{p}C_\ce{HA}$
Derive analytical solutions for the pH as a function of $\mathrm{p}C_\ce{HA}$ using the charge balance equation:
$[\ce{H^+}] = [\ce{OH^-}] + [\ce{A^-}]$
combined with the above inequalities for each Region. Because doubling $C_\ce{HA}$ corresponds to a $–0.30$ shift in $\mathrm{p}C_\ce{HA}$ as described above, the pH shift can be determined from the derived analytical
solutions. Calculate the pH shift when $C_\ce{HA}$ is doubled for Regions $A$, $B$, and $C$, respectively.

I was able to get the charge balance equation into the following form using $K_\mathrm{a}$ and $K_\mathrm{w}$:
$[\ce{H^+}]^2 = K_\mathrm{w} + K_\mathrm{a}C_\ce{HA}$
$$\mathrm{pH} = \frac{\mathrm{-lg}(K_\mathrm{w} + K_\mathrm{a}C_\ce{HA})}{2}\tag{1}$$
Using this I calculated the pH for region $A$ and got
$$\mathrm{pH} = \frac{\mathrm{-lg}(10^{-14}+10^{-3}\cdot10^{-(1-0.3)})}{2} = 1.85$$
Is this reasoning correct or am I understanding something incorrectly?


texts: Is there a relation between the ionization energy and the electron affinity?

texts: I am aware of the definition and equation of IE and EA. I was wondering if there is a direct relation between this two quantities with the energy of the neutral specie.


texts: Is coupled cluster variational for two electrons?

texts: I know that coupled cluster (CC) is not variational for the general case. However, if we only have two electrons with one nucleus, CCSD should be exact for this system like full configuration interaction (CI). Since full CI is variational, can we argue that CCSD is also variational for this special case?


texts:
It is observed that rate of reaction of two isotopologues of benzene, $\ce{C6D6}$ and $\ce{C6H6}$, is the same for electrophilic aromatic reactions, as the deprotonation is not the rate limiting step.  Instead the carbocation is usually limiting.

Do iodination and sulphonation somehow do show different rates with these isotopologues?  Is $\ce{C6H6}$ the faster of the two, due to stronger C-D bond (smaller size of D)? If this is correct what is the reason?

Does the protonation becomes the rate limiting step? if yes, then why in only with iodination and sulphonation?

Update : Found potential energy graphs for suphonation and nitration and it does seem like protonation either becomes the rate determining step or just smaller than carbocation hill, but why in sulphonation, the deprotonation curve was high is still a mystery.


texts: What is the acid dissociation constant of cacodylic acid?

texts: What is the $\mathrm pK_\mathrm a$ of cacodylic acid? I cann't seem to find one answer on the internet. I have read 1.67, 6.37, and 4.8 in my $\mathrm pK_\mathrm a$ table. What is the reason for this? Also, the problem I just did had it as 0.34.


texts:
I have a GC with a peak pair I'm interested in separating but are not getting resolved cleanly at the moment. Any tips on what temperature programming tweaks might help me?

The problem pair elutes at about 3.3 mins. The temp program was 120 C for 2 min followed by a 8 C/min ramp to 180 C & a final hold of 5 min.

Changing the column, detector or carrier gas is not an option. I want to just get the best I can by temp. programming optimization.

I've tried isothermal runs at 120 & 100 C but not much help. The peaks still come unseparated.

Since it is just this two peaks that interest me mostly, theoretically a ramp is superfluous isn't it? Just figuring out the right isothermal run ought to give me the separation of interest?

Edit:

The column is an OV-351 packed col. 2 m long and 1/8" in diameter. N2 carrier gas with FID. The molecules are:


texts: Interstitial sites: edge and face sharing?

texts:
In close packed structures there is one octahedral hole per close packed atom. In a HCP unit cell these octahedra form a chain of face sharing polyhedra. Is this this universal in close packing or only common to HCP?

More generally this question is "how do we know when interstitial sites (T± and Oh) share edges or a faces?"


texts:
The following question was asked in one of the assignments my teacher has given.

Acetone ($\ce{Me2CO^16}$) on treatment with $\ce{H2O^18}$ gives a mixture of $\ce{Me2CO^16}$ and $\ce{Me2CO^18}$, the
latter being in slight excess. This may be explained by
(A) hydration of acetone is an equilibrium process
(B) $\ce{C – O^18}$ bond is slightly stronger than $\ce{C – O^16}$
(C) $\ce{Me2CO^18}$ forms stronger hydrogen bonds than $\ce{Me2CO^16}$ with water
(D)hydration of acetone is irreversible

I have doubt about option (C). According to me, (C) should be correct, but it is given incorrect. Why the $\ce{^18O...H}$ is weaker than $\ce{^16O...H}$ bonding?


texts: Generate Surface with CubeFile from Gaussian in VMD or other free programm

texts:
I asked a question before, about how to save a mapped surface from GaussView. I don't get an answer, so I get much deeper in my internet research about it again.

Now I want to try to create a mapped surface of the electronic potential with VMD. So I found out, that I must create the cubefile before with gaussian. After that I import my cube file to VMD.
I followed multiple advises and introductions on the internet, but none of them worked for me.

I tried it also on my own, but this works not as well.
What musst I do on VMD or even when I create my cubefile on gaussian? Got somebody a proper link for me or can give me an advise? My target is to create a figure which can be used for publishing a thesis.

Thanks, Andrea!

If you need some files or something just let me know!


texts: Transferring suspended substance from isopropyl alcohol to water?

texts:
I have this UV-reactive invisible ink (a clear liquid.) According to the data sheet, it is suspended in an isopropyl alcohol base. Unfortunately, this is terrible for my particular application for two reasons: (1) it dries too fast (I need it to stay wet on a rubber stamp for ~15 minutes before stamping.) (2) It is too "thin" and thus bleeds into the porous material a little too much.

I've used regular black ink refills that (I believe) are water-based and they are perfect (except for the visible, non-UV-reactive part.)

If I understand this stuff correctly, the UV ink would be UV-reactive particles suspended in isopropyl alcohol base. If I were to mix this with water to get a workable liquid, I would likely dilute the ink too much.

Is there a way to transfer the suspended particles from the isopropyl-alcohol to water? Perhaps by mixing them, letting them separate and then let the alcohol evaporate off the top?

Alternatively, to reduce dilution I've considered finding a clear viscous liquid (think simple syrup without the stickiness) or even a clear gel as a thickening agent. Unfortunately, I don't know of a good viscous liquid or gel that would evaporate without a visible/sticky residue. Possibly one of the inactive ingredients in a hand sanitizer gel?


texts: Does anyone know if there's a tool for listing the functional groups present in a molecule?


texts: Ideal characterization technique to study behavior of heated metal nitrates

texts:
I have 3-4 metal nitrates as precursors for my coprecipitation reaction. I need to study the behavior of each individual nitrate and also of various combinations at 60 degrees Celsius, which is my experiment temperature. Which characterization technique would be most suitable to study the change in each case if any?

I have the following nitrates-

1)Barium nitrate

2)Aluminum nitrate nonahydrate

3)Iron nitrate nonahydrate

4)Cobalt nitrate hexahydrate

5)Cerium nitrate hexahydrate

The solvent is water for each solution. I need to know whether any nitrate will decompose or undergo any structural changes. I am trying to reach all these nitrates with ammonium carbonate to precipitate carbonates of all.


texts: Reduction of oximes with lithium aluminium hydride

texts:
I know that $\ce{LiAlH4}$ is good a reducing  agent and it donates hydride ions but then I am not able to understand the mechanism of this reaction.

I attempted this way

I am not understanding what to do with the extra charge on nitrogen as there is no acidic medium so that I can donate $\ce{H+}$ to it or can remove ($-\ \ce{OH}$) by any protonation.


texts: What is the precision of intensity data in XRD measurement?

texts:
I made some relative crystallinity measurements on a zeolite (crystalline aluminosilicate). Which is measured for a specific peak area and compared with a reference sample.
The XRD of powder patterns were recorded using Malvern PANalytical X’Pert PRO Diffractometer with CuKα radiation. The patterns are collected over a range of 3-60 °2θ with a time per step of 0.017 °s-1 using a quarter° divergence slit. In this setup the sample is rotated during measurement. I use Origin for integrated area peak calculation for 21-33 °2θ and the reference sample is made to 100%. We try to reduce the sample thickness error by putting the same mass quantity in all the holders.
I obtained some discrepancy within the data, within a 4% margin. I'm trying to find in the literature what is the margin of error when measuring intensity with XRD.


texts: Why is OTs a good leaving group and how does it work?

texts:
I've been told that $\ce{OTs}$ is a good leaving group for substitution reactions, but I'm not sure how it works or why it is a good leaving group. Can someone please explain?

$\ce{Ts}$ comes from Toluenesulfonyl chloride, and when the $\ce{Ts-}$ ion replaces and H in an alcohol, it becomes an $\ce{OTs}$ group.


texts: Why is the hydrogen adjacent to carbonyl carbon of aldehyde not acidic?

texts:
In $\ce{H^a-CH_2-CO-H^b}$, why is $\ce{H^a}$ more acidic than $\ce{H^b}$ ? From what I know, $\alpha$ hydrogen ($\ce{H^a}$) is highly acidic and is easily abstracted in presence of base $\ce{OH^-}$. But why is $\ce{H^b}$ not abstracted in the similar fashion?

$\ce{C}$ is electronegative because of the $+I$ effect it exerts on $\ce{O}$. Since, $\ce{H^b}$ is more nearer to the $\ce{C}$, shouldn't it be more acidic as the bond pair is more shifted towards the carbonyl carbon?


texts: Is there a commercial liquid with refractive index greater than n=2?

texts:
For an application I need a commercial, transparent liquid with refractive index $n>2$.

Is this kind of liquid available?
What's the chemical composition of this?

On the web, only $n=1.81$ is routine.


texts: Photocurable Polymer with no oxygen functional group or whose the structure is well known

texts:
I'm experimenting with the PDMS. I want to change the material with no oxygen containing functional group.

Is there a UV curable polymer with no oxygen atom?
Preferably cheap.

Or

Please recommend any UV curable or photoresist with well-known morphological property and molecular (polymer) structure.


texts: How many moles of methyl iodide will be consumed by one mole of crixivan?

texts:
My take on this question : a total of 5 moles of $\ce{CH3I}$ should be consumed.

The oxygen atoms in the $\ce{2 OH}$ groups each have a lone pair of electrons. They should displace $\ce{I-}$ from methyl iodide via an $\ce{S_N2}$ reaction.
The two nitrogen atoms in the tertiary amino moieties also should react with a total of 2 moles of $\ce{CH3I}$ .
The $\ce N$ atom in the pyridine moiety should also consume a mole, as the lone pair of electrons on it is not in conjugation with the benzene nucleus.

However, as I checked the answer, it's provided as 3. What may be the fallacy in my reasoning?


texts: I am looking for references (review articles, reports) about non-stoichometric compounds. Any idea of where should I look?


texts: What is the yellow compound formed in electrolysis of brine?

texts: Last week, I tried to conduct electrolysis of brine in my house using copper electrodes and 6V battery. After sometime, the entire solution turned orange/yellow. The yellow substance formed a kind of cloud at first and later it turned to an orange colloid. Does anyone know what the yellow coloured substance might be?


texts: Finding the mystery ester strucuture using NMR

texts:
I have an unknown ester with the chemical formula $\ce{C9H10O2}$ that is used as a flavoring agent in candies. It exhibits the following H-NMR and C-NMR (Attached file: unknown ester NMR)

Based on the NMR peaks I believe the unknown is benzyl acetate, as the C-NMR and the first two peaks of H-NMR are identical to the unknown NMR (Attached file: benzyl acetate NMR).

Knowing that aromatic protons are not equivalent, as shown in the unknown's H-NMR at 7.4 and 7.5 ppm, I do not know why the aromatic protons for benzyl acetate are integrated and shown as a singlet.

Is this just due to the sensitivity of the prediction algorithm (I am using Chembiodraw)? Or benzyl acetate is not the unknown?

Your help is greatly appreciated!


texts:
"Bonds will form only if the potential energy will be lower when the
atoms are bonded than when they are separate."

Is this statement true? If so, how do endothermic reactions exist? Can't you add energy to a system to make the bonds form albeit unfavorably?


texts: Precise estimation of air properties as a function of temperature at 1 atm

texts:
Are there any tables with empirical equations to calculate properties of air as a function of a temperature at 1 atm?
For example, NIST provides such equations for a large number of gases, but I was not able to find such solution for air, where I would specifically like to obtain:

Dynamic viscosity,
Specific heat,
Prandtl number,
Thermal conductivity,
Thermal diffusivity.

It would be best, if I could put these calculation in MS Excel, because I need to change these values with respect to temperature in multiple equations.


texts: Derivation of t2g eg splitting in octahedral field

texts:
I am trying to make the derivation of the d orbitals splitting under an octahedral field but I am kind of at a loss and don't know of any literature that can provide a more introductory level of this subject (if you know of any, please let me know).

I am trying to follow the book "Magnetic Oxides" by Gerald F. Dionne but I understand half of what it says in regards to this.

I know that we want to use the crystal field as a perturbation to the hamiltonian of the center ion, and for that you need to diagonalize the matrix (picture from here)

And that's it, that's where my understanding ends. The subscripts of this matrix is the quantum number m and the regular d suborbitals are almost all a linear combination of spherical harmonics with different m. So how do I diagonalize it?

The book doesn't do an explicit matrix handling and it basically just tells you from the start what the eg and t2g orbital are comprised of, I am assuming the notation means something I am unaware of,  and that they have different perturbation energies. No explicit equation that makes you understand that is shown.

I am sorry if it all seems confusing, I am confused. I know the how to derive the octahedral field (in cartesians and spherical harmonics) and how each d suborbital is written in spherical harmonics. But I don't know how to obtain the different energy splitting due to the perturbation of the octahedral field, any guidance/book or help is appreciated. Thanks!

PD: I am not a chemist, that's why I don't know of any books where I could read about this subject and why I am probably not following that well the book I was given.

Edit:

Because of all the recommendations, I have been able to understand more clearly the procedure while looking at it from a matrix perspective rather than a group theory one (completely at a loss there).

My question is that I am not getting what I should be when obtaining the element of the matrix

When trying to obtain those numbers in Mathematica I obtain values that don't make sense. I defined the d wave function like

Here you can see one matrix entry as an example

When doing the same as above for the four that appear in the image, I get that the factors before the Dq need to be

Which is not the same as the book.


texts: Electron donating ability of substituted amines on aromatic ring

texts:
How would you arrange the conjugate bases of the following amines in order of electron donating ability as EDGs as substituents on an aromatic ring?

$\ce{NH3}$, $\ce{(C2H5)(C2H4CN)NH}$, $\ce{(C2H4OH)2NH}$, $\ce{(C2H5)(C2H4OH)NH}$

I would think that the order would be:

$\ce{(C2H4OH)2NH}$ > $\ce{(C2H5)(C2H4OH)NH}$ > $\ce{(C2H5)(C2H4CN)NH}$ > $\ce{NH3}$

based on the reasoning that alkyls cause an inductive effect which increases electron density.

I think that pKa would be able to measure the electron donating ability of the conjugate base.

However, I found that $\ce{NH3}$ has a higher pKa (9.25) than $\ce{(C2H4OH)2NH}$ (8.96), which would mean that the conjugate base of $\ce{NH3}$ is a stronger base, which I don't understand.

Is my reasoning for the order incorrect? Or is the usage of pKa to measure electron donating ability of the conjugate base incorrect?


texts:
The first compound is said to be hydrolyzed more easily than the 2nd compound below under Alkaline medium . How is this possible ?

I thought due to resonance, -NO2 acquires negative charge which faces repulsion from the solvation effect by basic medium. But it will be relatively easier for oxygen in -CH3O( in 2nd compound) to donate its electrons to have it in resonance with benzene. But this contradicts with answer. Where am I going wrong?


texts: What is the difference between chemical equilibrium and dynamic equilibrium?

texts:
Is chemical equilibrium and dynamic equilibrium the same thing? Both point to the reversible reactions and no net changes in the concentrations of product and reactant.

Dynamic equilibrium from Wikipedia:

  In chemistry, and in physics, a dynamic equilibrium exists once a reversible reaction occurs. Substances transition between the reactants and products at equal rates, meaning there is no net change. Reactants and products are formed at such a rate that the concentration of neither changes.

Chemical equilibrium from Wikipedia:

  In a chemical reaction, chemical equilibrium is the state in which both reactants and products are present in concentrations which have no further tendency to change with time, so that there is no observable change in the properties of the system. Usually, this state results when the forward reaction proceeds at the same rate as the reverse reaction. The reaction rates of the forward and backward reactions are generally not zero, but equal. Thus, there are no net changes in the concentrations of the reactant(s) and product(s). Such a state is known as dynamic equilibrium.


texts: How does biodiesel have so much energy density?

texts: I find it fascinating that something like cooking oil can be turned into fuel. I know it can't have that energy density off the bat. So what do they do to make fuel for cars? Do they have to add other ingredients, and if so, why?


texts: Aluminum really wants to and will form aluminum oxide. Upon research, aluminum oxide is fairly unreactive. I wanted to ask if I had aluminum anode which would quickly form aluminum oxide (which is unreactive), will  that inhibit the aluminum from being oxidized? Basically, will aluminum metal loose electrons and become an aluminum ion?


texts: Why aren't resorcinol and catechol classified as dihydric alcohols? They contain two alcohol groups.


texts: What is the correct name of 3-isopropyl-4-methylhexane?

texts: In the branched alkane shown above, I've been told that 3-isopropyl-4-methylhexane is supposedly the correct name. However, in the alternative numbering scheme on the right, the parent chain is still of the same length (six carbon atoms) and has more substituents, so shouldn't that be the preferred name?


texts: Energy of photons emitted by de-excitation of electrons

texts: When an electron of an atom returns from an excited state to the ground state, it emits energy in the form of a photon. How does the change in energy level compare to the energy of the emitted photon?


texts: How to find a symmetry group of a system if all the symmetry transformations do not obey closure and don't form a group?

texts:
For instance, consider a system with $p_x$ and $p_z$ orbitals at the vertices of a square (on xy-plane). A square by itself would have $D_4$ symmetry. However, because of the $p_x$ orbital; the $90^\circ$ rotation ($C_4$) and $270^\circ$ rotation ($C_4^{-1}$) are no longer symmetry operations. Now the rest of the $D_4$ members do preserve the symmetry, but do not form a group since the subset is not closed.
How does one go about formulating a symmetry group for cases like these?


texts: Why is the more electronegative atom lower in energy in an MO diagram?

texts: Let's take $\ce{NO}$ for example. Why is $\ce{O}$ lower in energy? I asked my teacher and he said that because it is more electronegative and this lowers the bonding energy of the MO. But why?


texts: What chemical file formats are compatible with 3D printing?

texts: I would like to print some molecules rather than building them using a kit. What file formats work?


texts: Amber Force Field Improper Parameterization Huge Kb Problem

texts:
I am trying to parameterize a molecule. I know dihedrals and impropers are the same for Amber Force Field. (Source: http://archive.ambermd.org/201004/0334.html)
 So, I did PET scan for improper and I found this chart:

According to this chart and Amber7 manual Appendix-C I should define impropers like this in my mini-force field:

C-O-B-C 40.5 180.0 2.0

But in gaff and gaff2 the biggest improper values are not greater than 15
( here is gaff2: https://github.com/choderalab/ambermini/blob/master/share/amber/dat/leap/parm/gaff2.dat and here is gaff: https://github.com/choderalab/ambermini/blob/master/share/amber/dat/leap/parm/gaff2.dat)

And to compare my improper values with gaff, I scanned C-C-C-C impropers and I obtained almost the same chart as above but in gaff, this improper is defined like this:

C-C-C-C 1.1 180.0 2

(line 6693 : https://github.com/choderalab/ambermini/blob/master/share/amber/dat/leap/parm/gaff2.dat#L6693)

so it is obvious gaff doesn't use PES scan values for improper but it seems unreasonable because dihedral values fits with PES scan.
So what should I do? Should I use values which I obtained from PES scan ( C-O-B-C 40.5 180.0 2.0) or what should I do?


texts: Striking examples where Kohn-Sham orbitals clearly have no physical meaning

texts:
In Density Functional Theory courses, one is often reminded that Kohn-Sham orbitals are often said to bear no any physical meaning. They only represent a noninteracting reference system which has the same electron density as the real interacting system.

That being said, there are plenty of studies in that field’s literature that given KS orbitals a physical interpretation, often after a disclaimer similar to what I said above. To give only two examples, KS orbitals of H2O[1] and CO2 closely resemble the well-known molecular orbitals.

Thus, I wonder: What good (by virtue of being intuitive, striking or famous) examples can one give as a warning of interpreting the KS orbitals resulting from a DFT calculation?

[1] “What Do the Kohn-Sham Orbitals and Eigenvalues Mean?”, R. Stowasser and R. Hoffmann, J. Am. Chem. Soc. 1999, 121, 3414–3420.


texts: How can I build the molecular orbital diagram of the complex tetraammincopper(II) (square planar structure)?

texts:
I have to build the molecular orbital for the $\ce{[Cu(NH_3)_4]^{2+}}$ complex.

I know I have to use the characters table, the irreducible representations, the rule 5 and, somehow, determine the energy levels of the orbitals sigma and pi.

With this I should be able to build the MO but I don't know how to do it.

PS: I know we usually find this complex as $\ce{[Cu(NH3)4(H2O)2]^{2+}}$, but what I need is a theoretical answer to explain the $\ce{Cu-N}$ bond using MOT.


texts: Why does $\ce{CO2}$ make two π bonds? Why can't it make four σ bonds? Also, why do the π bonds not involve for repulsion?


texts: How is energy released when a chemical bond is formed?

texts:
Chemical reactions are classed as endothermic or exothermic.

Defn: exothermic

  (of a reaction or process) accompanied by the release of heat.

The heat is released when the chemical bonds in the product are formed.

Defn: heat

  heat is energy in transfer to or from a thermodynamic system, ... The
  mechanisms include conduction, ...; or radiation between separated
  bodies; or ....

So, I have three questions:

1 - if the heat is released via conduction, is this equivalent to an increase in the kinetic energy of the product(s) compared to the kinetic energy of the reactant(s)?  Also, how does the formation of a chemical bond produce kinetic energy?

2 - if the heat is released via radiation, how is radiation created in the formation of a chemical bond?

3 - are conduction and radiation the only forms of heat transfer when a bond is created?

Edit - to clarify the question - the issue is addresed in the OPENSTAX AP chemistry text - which covers one example of 2 H atoms coming together to form H2 in detail as follows:

  When the atoms are far apart ..... by convention the sum of their
  energies is 0. As the atoms move together their orbitals begin to
  overlap.  Each electron begins to feel the attraction of the nucleus in
  the other atom.  In addition, the electrons begin to repel each other,
  as do the nuclei.  While the atoms are still separated, the
  attractions are slightly stronger than the repulsions, and the energy
  of the system decreases. (A bond begins to form.) ... At some specific
  distance between the atoms, which varies with the atoms involved, the
  energy reaches its lowest  (most stable) value.  This optimum distance
  between the two bonded nuclei is the bond distance between the two
  atoms.

The text doesn't specify what energy is decreasing, and why.  But I can answer these questions I think.  The energy that is decreasing is the potential energies of the attractive fields of the atoms, and that energy is being transformed to kinetic energy as the atoms accelerate toward each other.

So we have the nuclei accelerating towards each other.  What happens next?

According to the text ... continuing where we left off

  The bond is stable because at this point the attractive and repulsive
  forces combine to create the lowest possible energy configuration.

So there is no mention of the release of energy, and the atoms just arrive at the stable combined state.

Here is what I would expect, given that the nuclei are accelerating towards each other - at some point the repulsive forces become stronger than the attractive forces, and the atoms begin to decelerate.  If there is no damping force on the motion the atoms will oscillate about the point where the attractive and repulsive forces are equal.  So, there must be some damping force on the atoms, that causes them to come rest at the bond distance of H2.

Now comes the mystery, which is, how does the formation of a chemical bond release energy?

What happens to the kinetic energy of the two nuclei accelerating towards each other?  If the two hydrogen atoms are coming together head on there will be a collision that would appear to cancel out the motion, i.e. kinetic energy, of both atoms.  If there is a damping mechanism that generates the heat, what is it?

Since the energy is released as heat, I think it must be in the form of kinetic or electromagnetic energy, but what is the specific mechanism?

Or, am I trying to get too much out of the kinetic model?


texts: Preparation of Grignard reagent. Free radical rearrangement

texts:
Mechanism of formation of Grignard Reagent
$$\ce{R-X + ^.Mg^. ->[\text{r.d.s.}] R^. + ^.Mg+X-} $$
$$\ce{R^. + ^.Mg+X- -> R-Mg+X-} $$

As the mechanism of preparation of Grignard reagent suggests, it involves the formation of free radical. And so, it is observed that racemic mixture is formed, in case the carbon on which the free radical is formed is chiral. But, why there occurs no rearrangement of this free radical ($\ce{R^.}$) ?


texts: Effect of substituents on arene oxide-phenol rearrangement

texts:
When I was learning about the reactions of epoxides from my textbook, I came across the following mechanism for arene oxide-phenol rearrangement in the presence of acid:

NIH Shift - National Institute of Health Shift (c.f. Wikipedia)

In the above example, there is no substituents on the ring and hence the final product remains irrespective of which $\ce{C-O}$ bond in the arene oxide cleaves to open the ring. Later, the author presented the following reaction where the ring has an electron donating group - methyl group:

Here the final product depends on which of the two $\ce{C-O}$ bonds in the arene oxide is broken. Based on the general reaction mechanism provided by the textbook, I derived the following mechanism to form the product prescribed by the author:

Before writing the above mechanism, I first arrived at a different product by following the mechanism given below:

The reason I initially chose to cleave the left $\ce{C-O}$ bond in "Reaction Mechanism - 2" was, it gives rise to the carbocation 2(a) where the methyl group is at the para position. I've learnt that methyl group stabilizes a positive charge by hyperconjugation. Since, resonance effect is felt only at the ortho and para positions and not at the meta position, the carbocation 2(a) is more stable than 1(a) from "Reaction Mechanism - 1". Moreover, in the first mechanism, NIH shift involves a 1,2 Deuterium shift whereas in the second it's a 1,2 Hydrogen shift. I find a deuterium shift to be slightly energy expensive process due to its higher mass and stronger bond with carbon compared to a hydrogen shift.

The only reason why I think the first mechanism is better than the second is the product 1(b) is more stable than 2(b). But I don't understand why is the second reaction not preferred over the first even though it has two factors supporting (stability of 2(a) over 1(a) and hydrogen shift over deuterium shift) it.

I faced similar contradictory results while writing the mechanisms for the following reactions (from the same textbook):

My questions are:

Are the reactions provided by my textbook correct?
If yes, why is the cleavage of one $\ce{C-O}$ bond of the epoxide preferred over the other even though it produces a comparatively less stable carbocation? Are there any other factors which determine which bond cleaves?
Is arene-oxide phenol rearrangement "specific" or highly "selective"? Or in simpler terms, does the rearrangement exclusively form only one product or does it form some small amount of the other product too?

Image source: My own work :) | Made using Marvin Sketch.
Textbook: Organic Chemistry by Solomons, Fryhle, and Snyder | Chapter 10: Alcohols and Ethers | Section 10.14: Reactions of Epoxides


texts: How to remove formaldehyde (smell) from clothes/jeans?

texts:
Bought several jeans, then to discover they have a really nauseating smell, that is not removed by washing. Reckon it's formaldehyde, from what I can read. Anyway, assuming you have jeans with formaldehyde in the fabric, what may effectively remove/neutralize this?

I ordered $\pu{10 kg}$ sodium bicarbonate for a soak, or I plan to heat them for a long time.  But advice from chemists is perhaps more productive. So, any ideas?


texts: Why is the oxidation state of Co -1 in [Co(CO)4]-?

texts:
In $\ce{[Co2(CO)8]}$, most people say the charge of $\ce{Co}$ is 0. How does it become $\ce{[Co(CO)4]-}$?

Most answers would say that $\ce{Co}$'s charge becomes -1. How does this work? -1 is not listed as the oxidation state of $\ce{Co}$ or any transitional metals.


texts: Do SN1 reaction always result in Racemisation

texts: In the following reaction the products formed are not enantiomers but are diastereomoers.So there is no racemisation occured.So is it always correct to say that SN1 result in racemisation?


texts:
What is the smallest whole number coefficent of $\ce {Cr^{2+}}$ when the equation is balanced?
$$\ce {Cr^{2+}_{(aq)} + Al_{(s)} -> Cr_{(s)} + Al^{3+}_{(aq)}}$$

I don't understand, how can this be balanced? And why would 3 be the smallest coefficient?


texts: How do I build a home-made apparatus for identifying what minerals are present in water?

texts:
While there are many readily available kits in the commercial market for testing the type of minerals present in water,

is there a way we can build one at home?

I am ready to spend some bucks on raw materials, if I can get the knowledge of how to build such apparatus


texts: How to rationalise the coordination number of CsCl versus NaCl?

texts:
Question:

  Suggest an explanation for the coordination number in the $\ce{CsCl}$ lattice being different from those in $\ce{NaCl}$.

Standard answer:

  Caesium ion is larger than sodium ion, hence it can be surrounded by greater number of chloride ions.

My questions:

The question didn’t specify whether it is asking for the coordination number of $\ce{Cs+}$ or $\ce{Cl-}$... Is it because the coordination numbers of both ions are the same?
The given answer sounds like each $\ce{Cl-}$ ion will be surrounded by less $\ce{Cs+}$ ions, how is it possible that the ratio of $\ce{Cs:Cl}$ is 1:1 (as from its empirical formula)?


texts: Entropy Changes in Electrolytic/Galvanic Cell?

texts:
One of the most fundamental equations in chemical thermodynamics states: $$ \Delta_rH_m^⦵ = \Delta_rG_m^⦵ + T\Delta_rS_m^⦵ $$
If we look at this equation in context of net chemical reaction in electrolytic or galvanic cell, it is usually interpreted as follows: Enthalpy of reaction denotes total amount of energy at constant temperature and pressure which needs to be supplied (electrolytic cell) or which is released (galvanic cell) during a reaction, standard Gibbs energy of reaction denotes what amount needs to be supplied or which is released in form of electrical energy (electric potential difference between electrodes), the last term including standard entropy of reaction denotes what amount of heat is exchanged with surroundings during a process.
In electrolytic cell, as entropy of reaction is mostly positive, last term is usually interpreted as heat which comes from surroundings and as such it increases entropy of the system. As heat comes to the system, it helps us during electrolysis since we don't need to put in the whole enthalpy of reaction in form of electrical energy, but only Gibbs energy. In galvanic cell it is the other way around.
What I don't understand is the interpretation of that last term ,which includes entropy of reaction, which I found on hyperphysics page. According to hyperphysics, this term denotes heat exchanged with surroundings and they say that entropy change in the system is due that heat exchanged.
I would say that entropy change is not due to heat exchanged, but due to the fact that during chemical reactions entropy changes because products and reactants have different entropies since they are different compounds with different structure and aggregate state. Entropy of reaction denotes such entropic changes and not entropy changes due to heat exchanged. What are your thoughts?


texts: Why are they called ‘dispersion forces’ if they are an attractice force?

texts: From the name, I thought dispersion forces would be repelling or dispersive forces between atoms, and not attractive forces. What is the dispersion part of the name actually referring to? Is it the electrons moving around?


texts: What is the correct Lewis structure for calcium phosphate?

texts:
In calcium phosphate, $\ce{Ca3(PO4)2}$, since the calcium and phosphate share an ionic bond, and the phosphorus and oxygen share a covalent bond, should the Lewis structure be like the following?

While I was checking other web pages I noticed there was another Lewis structure for the same molecule:

Are they both possible Lewis structures, or is the first structure the only "correct" version of the molecule?


texts: Why isn't hybridization done in America?

texts:
Warning: This is a question from my teacher.

In America hybridization isn't done, while in Europe it is done around the 10th grade. Is there any reason or advantage for doing(not doing) it as part of the school program?


texts: What is the mechanism of azulene synthesis?

texts:
In the Organic Syntheses preparation of azulene (http://www.orgsyn.org/demo.aspx?prep=CV7P0015) there are two reactions. First is a clevage of the C-N bond in pyridine and the second one is the annelation of a seven-memebered ring:

I suppose that the first step of the first reaction  is a nucleophilic substitution by pyridine at the 1-chloro-2,4-dinitrobenzene, but I have no idea how the mechanism could continue. Could some one please help me? Thank you.

Also, for the 2nd reaction, is it an electrophilic substitution at the cyclopentadieneyl anion, or does it have an  entirely different mechanism?


texts: How to calculate volume for NaOH and drano max gel (includes dilution and pH, pOH)

texts:
I have a question on an assignment that I don't quite understand. It says:

  What volume of $\pu{0.0100 mol/L}$ $\ce{NaOH(aq)}$ would have the same number of moles of hydroxide ions as $\pu{100.00 mL}$ of drano max gel?

The pH of drano max gel is $14.7$.

My first step was to switch from pH $14.7$ into mol/L. That turned out to be $\pu{5 mol/L}$ of $\pu{OH}$ concentration. Then I multiplied the $5$ by $\pu{100 mL}$ ($\pu{0.1 L}$) and got $\pu{0.5 mol}$. Now I don't understand how to get the volume needed. Would you use the formula for dilution ($C_1V_1 = C_2V_2$)?


texts: What do you think is a good way to explain electronic configurations?

texts: Understanding electronic configurations is vital, but a huge number of students face difficulties in understanding the why and the how. What approach do you think I should take in explaining electronic configurations to a student who only knows the Bohr model? Thanks.


texts: What kind of string to use for the ice fishing experiment for kids?

texts:
Classic ice fishing experiment for kids.

I used nylon because I saw it in a stationery, and apparently that doesn't work because I guess it's too slippery. I tried thread from my mom's sewing kit, but that doesn't work either.

I'm not sure I can find yarn or kite string in the stationery or nearby so please suggest alternatives expected to be found in the average household, supermarket, grocery store or convenience store.

Also how long should we wait? The above video takes only 10 seconds while this video takes about 2 minutes (off screen). What factors influence waiting time? Amount of salt? Type of string?


texts: Why don't ions have one equilibrium potential? (Nernst equation)

texts: I know that equilibrium potentials are dependent on the ratio of ion concentrations inside and outside of the cell and temperature. I also know that the equilibrium potential is reached when there is no net movement of ions across the membrane, i.e. the chemical and electrical gradients are equal. Why don't the ions move until they reach the same ratio of inside and outside concentration every time? For example, why doesn't ion "x" always diffuse until the ratio of inside to outside concentration is 15 to 1? Thanks in advance!


texts: Why is the alkene a more stable species in this case?

texts:
How can we account for $\mathrm{S_N1}$ substitution in this case versus elimination in others?
When we dehydrate alcohols, we usually carry out the reaction in concentrated sulfuric acid and at high temperature. The hydrogen sulfate ($\ce{HSO4-}$) present after protonation of the acohol is a weak nucleophile, and at high temperature the highly reactive carbocation forms a more stable species by losing a proton and becoming an alkene. (Emphasis mine) Furthermore, the alkene is usually volatile and distills from the reaction mixture as it is formed, thus drawing the equilibrium toward alkene formation. The net result is an $\mathrm{E1}$ reaction.
 (Solomons, 11th edition page 511)

The author seems to imply that the formation of an alkene from a carbocation is energetically more favorable than the formation of an $\mathrm{S_N1}$ product. Why?
Once the carbocation is formed, the step leading to the $\mathrm{S_N1}$ product requires the formation of a sigma bond whereas the step leading to the $\mathrm{E1}$ product requires the formation of one pi bond.
It seems to me that the $\mathrm{S_N1}$ product should be more favorable (not by a lot though, since the rate limiting step for both reactions is the same).


texts: how can electrons exchange from 3d orbital to 4s if their energy levels are not equal?

texts: I was taught that electrons only exchange in orbitals of equal energy or degenerate orbitals. The energy of 3d orbitals is 5 and that of 4s is 4(by n+l rule), but then how is it that in the case of copper and chromium electrons exchange from 3d orbital to 4s?


texts: If an electron moves closer to the nucleus in a given value of n, does it lose energy?

texts: If you look at a radial probability chart for a given electron sublevel (excluding n=1), there is a probability of an electron in that sublevel being closer to the nucleus. The electron should lose energy if it is closer to the nucleus because it experiences a greater force of attraction to the nucleus, but how is this possible if all electrons in a given sublevel have the same energy?


texts: Equalization of pressure in heat exchanger

texts:
I was solving numericals on Kinetic Theory of Gases when I came across this question

  Two closed vessel of equal volume contain air at 105 kPa, 300 K and are connected through narrow tube. If one of the vessel is now maintained at 300 K and other at 400 K what will be the pressure in the vessel?

I don't want the solution of this question but I want to know why the pressure will be same in both the vessel when one is maintained 300 K and other 400 K. The molecules in  the vessel at 400 K will have greater kinetic energy and will exert greater pressure on the walls than the molecules of the other vessel.

Now one will say that some of the molecules of vessel at higher temperature will move to the other vessel so that the pressure remains same in both the vessels, but why is it so. Why can't the pressure in both the vessels be different?


texts: How does life choose it's nominal temperature preferences?

texts:
If all life relies on water, and water freezes at 32F and boils at 212F.

Then why isn't the nominal temperature for life 122F?

122F will literally kill some animals, including us.

Do our biochemical reactions need "cold" (most people prefer ~72F) for some reason?


texts:
The question is to compare the SN1 reactivity for the following compounds. According to me it should be like R>S>Q>P.

But the correct answer is Q>P>R>S. How can a lone pair donating into a vacant p be more stable than allyl/benzyl carbocation?

These are the four compounds in the order PQRS respectively:


texts: Why does the hydride ion in LAH act as a nucleophile rather than a base in the reduction of carbonyl compounds?

texts:
Why does the $\ce{H-}$ ion in $\ce{LiAlH4}$ act as a nucleophile rather than a base in the reduction of carbonyl compounds ??

Because $\ce{H-}$ being a small ion would act as a better base than a nucleophile and I have been taught that it mostly acts as a base and it is very rarely that it is a nucleophile.

Also $\ce{H-}$ after extracting $\ce{H+}$ should become $\ce{H2}$ and leave the system, and also favour this reaction and move it forward.


texts:
In my inorganic class, we carried out the synthesis of chlorotribenzyltin, $\ce{SnCl(CH2C6H5)3}$.

The synthesis begins with a reflux I'll describe below:

In a hood, place 2.0 g (17 mmol) of 325 mesh tin powder, 4.0 mL of $\ce{H2O}$ and 6.0 mL (6.6 g, 52 mmol) of benzyl chloride in a 50 mL round-bottom flask. After the reaction mixture has been heated to reflux for 3 hours*, remove the heat and cool the flask in ice. The lower liquid phase should solidify to form a white solid.
*The white solids that appeared shortly after refluxing commenced should have largely disappeared, although small amounts of white or gray solids on the sides of the flask are usually still present. The reaction mixture at this point should consist of two liquid phases, plus a small amount of unreacted tin.

So the question the textbook asks is

Propose a chemical formula for the white solid that forms during the initial stages of the reaction of Sn with benzyl chloride.

I have a number of ideas as to what this could be:

The chloride bonded to the tin forming some kind of salt like
$$\ce{SnCl2}$$

The reaction did some kind of partial reaction creating something like
$$\ce{SnCl2R2}$$

The reaction went too far and created
$$\ce{SnR4}$$ and $$\ce{SnCl4}$$ and keeping them in reflux redistributed the ligands  based on stoichiometric amounts like
$$\ce{SnCl4 +3SnR4->4SnClR3}$$

This last one seems most likely based on supporting evidence from the text:

$\ce{SnCl4}$ reactions with Grignard reagents to give organotin compounds:
$$\ce{SnCl4 +4RMgX->SnR4 +4MgXCl}$$ ...
(it goes on to say)...the product, chlorotribenzyltin $\ce{SnCl(CH2C6H5)3}$, is a colorless solid that is stable in air for several days. In some respects, the reaction is analogous to the preparation of Grignard reagents, $\ce{RMgX}$ by treatment of magnesium metal with organic halides.

Is my reasoning for choice 3 solid? Is there something I'm not thinking of?


texts: How to demonstrate the safety of wearing leather shoes in the chemistry lab?

texts:
Quite often (from my own experience anyway), one of the safety rules in a school (high school or university) laboratory is that the students must wear leather shoes.

I like to demonstrate some of the safety rules, so my question is, what is an effective and safe experiment to demonstrate the safety of wearing leather shoes while experimenting in the chemical lab?

*This is in comparison to say sneakers or canvas shoes


texts:
Beta sheets have the peptide backbone parallel whilst the alpha helix has a curled backbone.
But the thing I can't get around my head is why would the same protein always fold into one of these shapes?
It looks to me like I could grab an alpha helix and just straighten it out to form a beta pleat. I can't see anything that wouldn't work - so if I could turn alpha into beta, then what ensures that these proteins will fold the same way each time they're made? I think there must be something that prevents me from turning alpha into beta but I'm not sure what.


texts: How is hybridisation of a carbon atom determined by looking at the molecule's structure and observing the lone pair and/or sigma bond present?

texts: How can I judge the hybridization of a carbon atom of any carbon containing compound just by looking at its structure? How can I say this by the help of lone pairs and sigma bonds present?


texts: How to create different fluorescent colors using household items

texts:
This is a request:
I wanted to create fluorescent liquids that have different colors.

I'm going to dye my flowers in different fluorescent colors and I'd need a recipe for fluorescent colors that aren't too toxic.

Please bare in mind that the injection of the liquid can only happen by spraying or watering with the liquid.

The liquid needs to be able to handle being Waterdown by tap water.

I'd recommend using household items to make this more helpful to the average day user. Also any color will do but, the most wanted Colors are:

List item

Blue
Green
Red
Yellow


texts:
I am seriously confuse with the sign of electric field in the electrical double layer. Say zinc is dipped into the zinc sulphate solution. Then why the electrical double layer has positive sign in the electrode side of EDL and negative sign in the electrolyte side of EDL.

I am confused that since zinc has more tendency to dissolve, then zinc should lose two electrons and retain those 2 electrons in the electrode side of the metal-electrolyte interface. This will give eletrode negative sign. Also a layer positive charge of $\ce{Zn^2+}$ develops parallel to electrode.
Where I am wrong here?


texts: Enantiomers to diasteroisomers (rotational spectra)

texts:
Enantiomers have identical rotational spectrum because their mass distributions are identical. Recently a trick has been introduced in microwave spectroscopy in which a enatiomerically pure gas chiral "tag" is introduced along with the enantiomers of the analytes in the gas phase. The chiral tag forms gas phase weakly associated diastereoisomers with the enantiomers, and those two diastereoisomers have a different microwave spectrum.

Will the two diastereoisomers, obtained from the two enantiomers, have different center of mass and moment of inertia, i.e., why would they have different rotational spectra?


texts:
Question:

Why do hydrogen compounds from the third period down (that are electron deficient or have completed octets) readily decompose?

Thoughts:

Apparently, heavier group 14 elements form hydrides which decompose readily because they have valence orbitals with which $\ce{O_2}$ and $\ce{H_2O}$ can coordinate. But I've tried and tried and cannot think of why this makes $\ce{CH_4}$ more stable than $\ce{SiH_4}$. What is the difference between the two (except for the fact that silane contains a larger central atom)?

As for the remaining groups on the periodic table, I cannot fathom how this trend holds.


texts: What are the products of the dissociation of sodium bicarbonate in water? What is the relative pH of the solution?

texts:
I had a recent question on a test that asked what the products would be if sodium hydrogen carbonate were dissolved in water. I had a few candidate answers

$\displaystyle\ce{NaHCO3 -> Na+ + HCO3-}$, but that one doesn't involve water at all
$\displaystyle\ce{NaHCO3 + H2O -> Na+ + OH- + H2CO3}$, but doesn't $\ce{H2CO3}$ decompose into $\ce{H2O + CO2}$?
$\displaystyle\ce{NaHCO3 + H2O -> Na+ + OH- + H2O + CO2}$, but that has water on both sides of the equation.

Part two of the question asked whether the solution would be acidic, basic, or neutral. What is the proper reaction for this?


texts: Is HPLC the best way to detect residues from anti-coagulant rodenticides

texts:
I am a beginner chemistry student studying anticoagulant rodenticides. The literature shows that high-performance liquid chromatography (HPLC) with fluorescence or UV light is the most commonly used method for the detection of residues in tissue samples. I want to understand on a basic, conceptual level why this particular analytical method is the preferred method.

I understand that HPLC can separate complex organic compounds and enable detection at extremely low concentrations, but I do not know whether there are other analytical methods that can also do this.

Is this particular analytical method more effective in detecting the presence of residues from anticoagulant rodenticide in tissue samples? If so, why? Is the answer related to the chemical properties of the compounds in rodenticides (hydroxycoumarins and indandiones)?


texts:
I have seen certain metals such as Aluminium used in a situation where it is in a powdered form and "compacted" into a shape under intense pressure (in a mould), and it ends up looking mostly like solid metal. It is also heated afterwards, I assume to form a complete metallic bond.
I have a few questions on this:

How are oxide layers on the powder affected when it is compacted? Eg. Can the $Al_2O_3$ layer, or at least the O atoms from them, be "inside" the moulded object when it is compacted?
Metals in a powdery form aren't as reflective as in their "solid" form (also please let me know the right word for that). Why is this?
Are most metals in their powdered form pure, eg. Not like a salt, but a single element?
I know gold powder, obtained from chloroauric acid, becomes gold in its metal form when melted down. It looks brownish and takes up far more volume than the gold it contains. Is this pure Au or a compound/salt?
Also, in 4. with the gold powder, it actually forms rather large clumps from the chloroauric acid. How is this possible assuming it's a pure element?

Thought I better get all the questions done in one go. Thanks in advance


texts: Basic behaviour of bromide ion with sulfuric and phosphonic acid

texts:
I  recently came across these two reactions:

  $$\begin{align}\ce{2KBr + 3H2SO4 &-> 2KHSO4 + Br2 + SO2 + 2H2O}\tag{1}\\[0.6em]
\ce{KBr + H3PO4 &-> KH2PO4 + HBr}\tag{2}\end{align}$$

I understand that the bromide ion being the conjugate base of a strong acid $\ce{HBr}$ is a very weak base and therefore it cannot take $\ce{H+}$ from a very strong acid $\ce{H2SO4}$ in the first reaction. But the second reaction is an acid-base reaction.

I checked the $\mathrm{p}K_\mathrm{a}$ values of $\ce{H2SO4}$ and $\ce{H3PO4}$ to find that $\ce{H2SO4}$ is a way better acid than $\ce{H3PO4}$, then why is that bromide ion could take $\ce{H+}$ from $\ce{H3PO4}$ but not from $\ce{H2SO4}$?

The first reaction is a redox reaction and I understand that redox reactions take place when acid-base reactions are not possible because acid-base reactions are quick. Then why is the first reaction not an acid base reaction?


texts: Is this problem doable with the information given?

texts:
Can I solve this problem without knowing any starting amounts?

An element $\ce{X}$ forms iodide ($\ce{XI3}$) and chloride ($\ce{XCl3}$). The iodide is quantitatively converted to the chloride when it is heated in a stream of chlorine:

$$\ce{2 XI3 + 3Cl2 -> 2XCl3 + 3I2}$$

Calculate the atomic mass of $\ce{X}$. Identify element $\ce{X}$.


texts:
I have the following question:

Which of the following would not be used to measure changes in atmospheric gases?
i) Satellites
ii) Mass Spectrometer
iii) Digital Thermometer
iv) Fractional Distillation

I assumed it would be fractional distillation since you cannot really measure anything with it? You only separate the fractions of different materials such as crude oil.
However the answer was Digital Thermometer. I guess I can understand how this object would be useless at measuring atmospheric changes relating to gases however how would you detect atmospheric gases changes using fractional distillation?


texts: Does the synthesis method used to make graphene oxide composites matter?

texts:
I'm doing a research project to test the photothermal conversion performance of graphene oxide composite materials.

We're using a number of different metals and metal oxides ($\ce{Au}$, $\ce{Ag}$, $\ce{Cu}$, $\ce{TiO2}$, $\ce{SnO2}$, etc.) and for each material the literature suggests different methods of synthesis.

We are only using chemical methods; the ones suggested include microwave-assisted reduction, redox reactions, and hydrolysis. Will using different methods of synthesis for each compound have an effect on the outcome of the experiment? Should the same (or similar) method be used for all of the composites?


texts: Inconsistency in Elementary Bi-Molecular Reaction Rate Expressions

texts:
Assume the following bi-molecular reaction is elementary as written with rate constant $k_\mathrm{f}$:
$$\ce{A + A -> P}$$
This review, suggests to express the rate in terms of the production of product "P":
\begin{align}
\frac{\mathrm{d}[\ce{P}]}{\mathrm{d}t} &= k_\mathrm{f}[\ce{A}]^{2},&
\text{where }
\frac{\mathrm{d}[\ce{P}]}{\mathrm{d}t} &= \left(-\frac{1}{2}\right)\frac{\mathrm{d}[\ce{A}]}{\mathrm{d}t},
\end{align}
which gives:
$$\frac{\mathrm{d}[\ce{A}]}{\mathrm{d}t} = -2k_\mathrm{f}[\ce{A}]^{2}.\tag{1}$$
While this other review suggests that the rate be written in terms of the consumption of reactant "$\ce{A}$":
$$\frac{\mathrm{d}[\ce{A}]}{\mathrm{d}t} = -k_\mathrm{f}[\ce{A}]^{2}.\tag{2}$$
Which is correct?


texts: Why are lactones more acidic than esters?

texts:
Lactones ($\mathrm pK_\mathrm a \sim 25$) tend to be more acidic than esters ($\mathrm pK_\mathrm a \sim 30$). I know that the lactone is fixed in a (E)-conformation, due to the ring:

and that in normal esters, the (Z)-conformer is favoured based on an anomeric effect, namely the donation of the $\mathrm{sp^2}$ lone pair on the ester oxygen into the C–O σ* orbital (image taken from Clayden, Greeves & Warren, Organic Chemistry, 2nd ed. (OUP), p 805):

Is this effect responsible for the increased acidity? If so, how?


texts: Why does a hydride like NaH act as a base, but a hydride like NaBH4 act as a nucleophile?

texts:
A TA talked about this today in the context of ketones.

If you stick an acetone and $\ce{NaBH4}$ together in a protic solvent, you get 2-propanol.

If you stick acetone and $\ce{NaH}$ together, you get an enolate. What's the difference? They're both hydrides.


texts: How to clean copper(II) sulfate crystals from sulfuric acid?

texts:
I am going to prepare copper(II) sulfate by electrolysis with sulfuric acid for crystal growing.

How would I separate the copper(II) sulfate from the sulfuric acid left over from the electrolysis process in solution?

I think, one way would be to make copper(II) oxide and mix it with the solution so that I get more copper(II) sulfate out of the solution by using left over acid. Then separating copper oxide would be easy.


texts: Changes in freezing point of sodium acetate

texts:
Background:
I was recently playing around with some reusable heat packs, the kind that operate by phase change of sodium acetate trihydrate and noticed that they didn't reach the temperature that I had expected (58 °C) rather, they stayed at 52 °C.

There were two such packs, roughly 50 mm × 100 mm × 15 mm and placed together with the broad sides in contact. Between them and at the center, there was a calibrated PT-100 RTD (which I certainly trust to be better than 1 °C accurate). The entire mass was then insulated with a few layers of thick wool fabric. The temperature reading became constant at 52 °C within a few minutes of crystallization being initiated in both packs and remained very stable for more than 10 minutes thereafter.

It's worth noting that although the manufacturer labeled the contents as being 'Sodium acetate (food grade)' and water, no proportions are given. Also, the contents of the pack are bright red, indicating the presences of unlisted dyes.

Question:
What would be the most likely causes for the discrepancy? Contaminants, incorrect, proportions something else?

I'm ultimately interested in using this reaction to maintain ~58 °C in an experiment. I'd like to avoid the same result if I mix up a batch of this stuff from pure ingredients.


texts: How to write a reaction that you have never seen?

texts:
I have been studying chemistry for a while but I feel a total noob about it, so please be clear when answering.

I was studying and I encountered this exercise:

  Write the reaction between copper and concentrated nitric acid.

Now, I know what copper is and also what nitric acid is, but how do I figure out that the reaction gives $\ce{Cu(NO3)2 + NO + H2O}$ ?


texts: Which azo compounds are found in DVD-R and CD-R media?

texts: Does anyone know which specific azo compounds are used in DVD-R/CD-R recordable media?


texts: Computing the bond spring constant from first principles

texts:
Given a set of atoms and their positions in space, is there a way to compute the bond spring constant for each pair of atoms that are considered to be bonded (I can already determine the bonds with OpenBabel)? I don't want to rely on empirical data, and it's okay if the spring constant is wrong by up to about 20%. I already know the bond length and bond energy, if that helps.

For background: my ultimate goal is to compute the normal modes of a molecule, by finding the generalized eigenvalues of an undamped mass-spring system. I already know the mass matrix, but I don't know the stiffness matrix.


texts:
The concentration is connected to the activity via
$$a(\ce{A})= \gamma_{c,\ce{A}}\cdot{}\frac{c(\ce{A})}{c^\circ},$$
where the standard concentration is $c^\circ = 1\:\mathrm{mol/L}$. At reasonable concentrations it is therefore fair to assume that activities can be substituted by concentrations, as
$$\lim_{c(\ce{A})\to0\:\mathrm{mol/L}}\left(\gamma_{c,\ce{A}}\right)=1.$$

The partial pressure is connected to the activity via
$$a(\ce{A}) = \frac{f(\ce{A})}{p^{\circ}} = \phi_{\ce{A}} y_{\ce{A}} \frac{p}{p^{\circ}},$$
with the fugacity $f$ and the fugacity coefficient $\phi$ and the fraction occupied by the gas $y$, the total pressure $p$, as well as the standard pressure $p^\circ=1\:\mathrm{bar}$ or traditional use of $p^\circ=1\:\mathrm{atm}$.
For low pressures it is also fair to assume that you can rewrite the activity with the partial pressure $p(\ce{A})$, since
$$\lim_{p\to0\:\mathrm{bar}}\left(\phi_{\ce{A}}\right)=1,\hspace{10ex} p(\ce{A})=y_{\ce{A}}\cdot{}p.$$
Now my question is since we can approximate activity to partial pressure as well as concentration therefore pressure must approximately equal to concentration. However we know that $p=cRT$, where $c$ is the concentration, hence we definitely cannot approximate pressure and concentration. So how is this possible?


texts: How can I solve a problem like this, "what is the eletronic distribution of Iron in layers"

texts:
What is the eletronic distribution in layers of Fe?
a) 2 – 8 – 10 – 2.
b) 2 – 8 – 12.
c) 2 – 8 – 8 – 4.
d) 2 – 8 – 18 – 18 – 8 – 2.
e) 2 – 8 – 14 – 2.

What is the approach to aswers this question?
I can draw Linus Pauling diagram by heart. I also know that each layer has a number of electrons it can suppor k = 2, L = 8 and etc. With my knowledge I cannot solve this question. My answer would be like this, "because the atomic number of iron is 26 it would be 2-8-8-8. But this isn't an available choice.
If a use the Linux Pauling diagram I get an answer if use the rules of distribution I get another answer.


texts: Are fractional oxidation states possible?

texts:
To get the oxidation state of carbon (denoted $x$) in octane, $\ce{C8H18}$, I used the fact that hydrogen has an oxidation state of $+1$:

$$8x + 18\cdot 1 = 0 \qquad \Longrightarrow \qquad x = -\frac{18}{8} = -2.25$$

But in that way, I get an oxidation number that is fractional, or not an integer. Is that normal?


texts: How does adding sodium chloride to a solution of copper sulfate change the equilibrium?

texts: In school we had a lesson about chemical equilibrium. We performed an experiment: in two tubes we poured $\pu{5 mL}$ of $\ce{H2O}$ and placed $\ce{CuSO4}$, the concentration of the $\ce{CuSO4}$ should have been $\pu{0.5 mol/L}$. We homogenize the two solutions in the two tubes and both solutions I think became blue (might have been green, not sure). Then we were asked to put a gram of $\ce{NaCl}$ in one of the tubes and homogenize. The color of the solution changed (also we might have added another $\pu{5mL}$ to the first solution, the one without $\ce{NaCl}$). Can someone tell me what do they think was the purpose of this lesson and how does it correlate to chemical equilibrium?


texts:
Why does magnesium insert itself between a carbon atom and halogen atom? Can anyone give any vague idea about why this occurs?

Also does a Grignard reagent only form when there is carbon atom and halogen atom with single bond between them? For example, can magnesium insert between the carbon and oxygen atoms of a carbonyl?


texts: Order of dipole moments of chlorine substituted methane (CH3Cl, CH2Cl2, CHCl3, CCl4)

texts:
In my book, the order of dipole moment for CH3Cl, CH2Cl2, CHCl3 and CCl4 is given as:

CH3Cl>CH2Cl2>CHCl3>CCl4

The way I understand this is—

  In case of CCl4, tetrahedral symmetry exists. Therefore, the dipole moment of three C-Cl bonds on one side, gives a resultant moment that is equal and opposite to the dipole moment of the single C-Cl bond on the opposite side. So, $\ce{\mu=0}$.

This explains CHCl3>CCl4.

  Again, in case of CHCl3, the three C-Cl bonds point to one side, so a moment equal to C-Cl bond is generated as a result. A moment of C-H bond is added to it. In CH2Cl2, the moment of two C-Cl bond is added at $\ce{109^\circ}$(approx.) so the resultant is greater than on C-Cl bond.

This explains CH2Cl2>CCl4

  In case of CH3Cl, the dipole moment of one C-Cl bond is added with moment of one C-H bond (resultant of three C-H bonds).

But this should mean moment of CHCl3$\ce{\approx}$ moment of CH3Cl, but clearly this is not so.
Where did I go wrong?


texts: What type of bond forms between an ionic compound solute and a polar solvent

texts: I understand the idea that the solvation enthalpy (ΔH-) must exceed the lattice enthalpy (ΔH+) for a solution to be more energetically stable, but what type of bond is formed between the disassociated ions and the the polar solvent molecules? Surely it must be even stronger than the ionic bonding in the lattice if it releases more energy than the energy needed to break the ionic bonds in the ionic compound.


texts: Maximum absorption wavelength directly proportional to the donor number of the ligand for a copper(II) coordination complex

texts:
I am looking at a set of results showing a directly proportional relationship for an increasing maximum absorption wavelength (UV-Vis spectra) with increasing donor number of solvent ligands. The complex has a $\ce{Cu^2+}$ centre with $\mathrm{d^9}$ electronic configuration. Assuming a tetragonal configuration, how does this tie in with ligand strengths?
I am not sure what I can deduce here as I thought the more available a lone pair (basicity) would be able to interact more strongly, a higher wavelength indicates the energy gap between the $\mathrm d_{x^2-y^2},$ and $\mathrm d_{z^2}$ orbital has decreased. So, has there been more significant Jahn–Teller distortion, or is the splitting parameter somehow smaller?
Where does my reasoning fall down?


texts: How to calculate the heat absorbed by a reversible process?

texts:
Given a nonideal substance inside a box with diathermal walls, the pressure is increased reversibly. How do you calculate the heat absorbed?

I assume we use

dE = dq + dw = dq - pdV

=> dq = dE + pdV

But I'm not sure how to deal with the "dE" term.


texts:
I recently freezed a huge bunch of apple slices, and thawed them again a few days later. After thawing, I noticed a few things compared to a batch that I had put in the fridge (no freezing)

The apples turned brown far quicker
After pureeing, they tasted sweeter

I know that slow freezingg can destroy cell walls in animals due to crystallization. My guess what has happened here is that the same mechanism also broke up long chain sugar polymers. Thus the sugars are chemically more active, oxidize more easily after contact with air, and taste stronger than in the other batch.

But is my guess plausible? Do polymers actually break under those mechanical stresses? Is this or a similiar effect observed elsewhere?


texts: Why does iodine get oxidized to iodic acid and not periodic acid by nitric acid?

texts: Nitric acid oxidizes iodine to iodic acid, $\ce{HIO3}$ and not periodic acid, $\ce{HIO4}$, which is of a higher oxidation state. This happens although other nonmetals are oxidized to their highest oxidation state. How can this be explained?


texts: Distinguishing propan-2-ol from ethanol using IR spectroscopy

texts:
A question requires me to distinguish between propan-2-ol and ethanol from IR spectra. To me, they both look nearly identical, even though I know both of them contain the same functional group and that IR spectra are only capable of identifying functional groups.

My question is, how do you distinguish the two, without using a mass spectrometer?


texts:
Chemical engineers define one mole as the amount of a substance which possess as many entities as $12\ \mathrm g$ of $\ce{^{12}C}$.

The number of atoms in $12\ \mathrm g$ of $\ce{^{12}C}$ is $6.022 \times 10^{23}$ which is a constant by its definition.

Now come to the relevant definition which is given in my textbook that defines one mole of a substance as the atomic mass, molecular mass or formula mass in grams.

Is this definition correct?


texts: Catalyst and Inhibitors home experiments

texts:
My teacher assigned me a science experience involving catalysts and inhibitors at home.
I think I understand the principle of it, but I fail to find possible experiments that I can do at home with a thermostat and some home substances.
The experience:
3 reactions...
1 with the catalyst,
1 with the inhibitor,
1 without anything.
I will compare them by measuring the reaction speed with a factor (preferably the heat variation).
EDIT: I can also measure the volume of the product.
Thank you.


texts: How to decide anode and cathode form electrochemical series?

texts:
To calculate cell potential one must know that from given half reactions which metal is to be anode and which is cathode.

So from standard reduction potential in electro-chemical series how to find this ?

If one element(say A) is above another element(say B) in the series then which is cathode A or B ?


texts: If "Gas" belongs to "State of Matter" then what does "Metal" belong to?

texts:
My question is, if "gas" belongs to "State of Matter" then what does "Metal" belong to.

Gas can be substituted with any state of matter(in the analogy); metal can be substituted with metalloid or nonmetal(in the analogy). I've researched this and I can't seem to find an answer to this. So, this could read as "if 'solid' belongs to 'State of Matter', then what does 'nonmetal' belong to'"?

I'm not trying to assert that metal is a state of matter.
As most of y'all (hopefully all) know, the elements on the periodic table can be a metal, metalloid, or nonmetal. Would "Metal" belong to "Metal Status"? I'm asking because I'm writing a program to represent the PeriodicTable and I need an appropriate name for my variable. I may just opt for "Metal Status".


texts: How is the Rate law of a reaction measured?

texts:
What is the Rate law of the reaction below?
$$\ce{4 HBr + O2 -> 2 H2O + 2 Br2}$$

How do we approach finding the rate law of a reaction? Can this be found out only through experiments?


texts: Calculate Michaelis-Menten constant of enzyme catalyzed reaction

texts:
I have:
$$\begin{array}{c|c}
\dfrac{v }{ [S]}/\pu{s^{-1}} & v \cdot 10^2/\pu{mol dm^-3 s^-1} \\ \hline
0.257\ & 5.15\\
0.895 & 4.48\\
2.00\ & 3.35\\
3.59\ & 1.8\\
4.82\ & 0.48\\
\hline
\end{array}$$
And I want to calculate $K_M$ graphically.
I know that I should use the equation:
$$\frac{1}{v}=\frac{1}{v_\mathrm{max}}+\frac{K_M}{v_\mathrm{max}[S]},$$
and that I should plot $1/v$ against $1/[S]$, and then the slope will equal $K_M$/$v_\mathrm{max}$.
I began with converting the data given from $v/[S]$ to $1/[S]$ by dividing each data point with $v$. This gave:
$$\begin{array}{c|c}
\dfrac{1}{[S]}/\pu{dm^3 mol^{-1}} & v \cdot 10^2/\pu{mol dm^-3 s^-1} \\ \hline
4.99*10^{-4}\ & 5.15\\
0.0019 & 4.48\\
0.0059\ & 3.35\\
0.0199\ & 1.8\\
0.1004\ & 0.48\\
\hline
\end{array}$$
Plotting $1/v$ against $1/[S]$ gives the graph:

But when I want to calculate $K_M$ through:
$$\text{slope} \times V_\mathrm{max} = \text{slope} \times \frac{1}{\text{intercept}}$$
I don't get the answer which is in our answer key. Unfortunately, only the answer for $K_M$ is given, and not how to get the answer. The answer is $K_M = \pu{0.0102 mol dm-3}$. Could someone explain where I am going wrong?


texts: Calculating concentration of dissolved ions

texts:
A sample of $\mathrm{2.00~g}$ of iron(III) sulphate is dissolved in water to give $\mathrm{100~cm^3}$ of aqueous solution. What is the concentration of $\ce{SO4^2-}$ ions in $\mathrm{mol~dm^{-3}}$?

My attempt:

I found the number of moles which is $\mathrm{0.005~mol}$.

Then, 1 mol of iron(III) sulphate has 3 mol of $\ce{SO4^2-}$

So the concentration is $\mathrm{\frac{0.005}{0.1} \cdot 3 = 1.5 \cdot 10^{-1} ~mol~dm^{-3}}$

But the given answer is $\mathrm{1.5 \cdot 10^{-2}~mol~dm^{-3}}$. Why?


texts: Why is the IUPAC name of glycerol expressed in the way that it is?

texts:
I have come across the name trihydroxy propane for glycerol, which I think should've been Propan-1,2,3-triol.

Why is it named this way? Is there any  other rule of nomenclature working?


texts: How do potentiometric cells do not proceed through a spontaneous reaction like in a galvanic cell?

texts:
It seems to me that the cell setup of a galvanic cell is pretty much the same as in a potentiometric cell. However, galvanic cells just proceed the spontaneous direction of the net redox reaction of the anodic and the cathodic species in the cell, while in a potentiometric cell, it seems that the equilibrium activity ratios of the measured solution are not to be affected.

I've read that in a galvanic cell, current flows as to follow the natural tendency of electron flow--from the anode to the cathode. But in a potentiometric cell, it's said that the current of electrons flowing is kept to a minimum. How does a potentiometric cell does that? How does it avoid for reduction at the measured cell or oxidation at the reference electrode to happen?

P.S. I know that the question looks uncohesive, but it's because I'm really confused how these concepts occur. Please try to clear up the misconceptions that might have been apparent from my question.


texts: Why is 11-oxabicyclo(4.4.1)undeca-1,3,5,7,9-pentaene aromatic?

texts: I have been told by my instructors that for a compound to be aromatic, it must be planar. In this given molecule the oxygen seems to be out of the plane of the conjugated system: how can it still be aromatic, then?


texts: Why do Alpha particles not collide with electrons during alpha decay?

texts: Alpha particles are positively charged, so my question is that during alpha decay, when these are released from the nucleus, why doesn't it ever occur that they collide and grab an electron or two since they are essentially a Helium nucleus?


texts: What is the largest one step radical cyclization ever achieved?

texts:
When I was an undergrad, roughly around 2005, I took a grad level class that covered various topics in advanced organic synthesis. I don't remember much clearly from the class, but one thing that I can't forget was this one reaction where a single chain compound was, in one step, cyclized to a multi-ring system (maybe 4 rings) via radical cyclization. This cyclization was precipitated by the release of N_2 from an azido group.

It was similar to the cyclization of squalene into lanosterol, but it was not enzymatically catalyzed. I can remember being absolutely astounded that nature had figured out how to do this, and then to later learn that some crazy bastard had done something similar without protein scaffolding was extremely humbling.

I unfortunately can't find my notes from that class, and my google searching hasn't helped me, either. I will try to reach out the original professor, but I think that's a long shot. And it's of course possible, in all honestly, that I could be misremembering it. But, I still have a fuzzy photo in my memory of the lower left hand side of a page of a journal article where this reaction was drawn out. If only I had enough detail to draw it!

So, I guess I'll just ask a more general question to the community. What is the largest single step cyclization that you are aware of? By "largest", I mean "number of atoms that end up as part of a ring that were not originally part of the ring". Very large diameter, single bond/ring radical formations are entropically unlikely, so that should be a fair metric.


texts: How to determine the order of elution in silica gel column chromatography?

texts:
Benzofuranoids ustusoranes A (1), B (2), and E (3) were isolated from Aspergillus ustus 094102. If these compounds were separated by column chromatography on silica gel, what would be the elution order? (top — comes off the column first, bottom — comes off last).

As I get it, column chromatography is like TLC where in a silica gel the nonpolar compound comes out first.


texts: Which causes of quenching increase specifically in electrochemical experiments?

texts:
If quenching is seen as a result of running electrochemical experiments on a solution, what kind of processes may be responsible? I'm thinking about UV/Vis spectroscopy, if it makes any difference.

The redox couple would be iodide ions, $\ce{I-/I^3-}$. I understand iodide ions to be quenching agents, so my suspicion would be that their varying concentrations would cause a variation in quenching over the course of the experiment.


texts:
I have used some of those lead check swabs from 3M. I used them on some ceramic tile and received strange results. I called the tile manufacturer who was insistent that lead had never been used in their operations. After talking with 3M they asked me to send a picture, which I did. After looking at the picture the 3M lab told me that they did not believe the test to be positive for lead but didn't explain the color I observed.

I realized I had cleaned the floors with a cleaner which contained silver citrate as a preservative. Would the silver ions have reacted with the rhodizonic acid? What color would this have produced? I observed a pinkish color (definitely not red. More pink/purple) in some areas I tested.

I can include a picture if it would help.


texts: Inductive vs hyperconjuative effects in electrophilic aromatic substitution

texts:
$\ce{C6H5C(CH3)3}$ is attacked faster than $\ce{C6H5CH3}$  in nitration, presumably because of the greater +I effect. However, for chlorination $\ce{C6H5CH3}$ is attacked faster i.e hyperconjugation takes over. Why?

One explanation given in my textbook is that chlorination is a less polar reaction. But I don't understand how that affects the relative importance of hyperconjuative/inductive effect.


texts:
I wonder if ethers are more or less acidic at the alpha position than alkanes ($\mathrm{p}K_\mathrm{a} \approx 50$). I'm not sure if the stabilising inductive effect from oxygen or the alpha effect (the repulsion between lone pairs on the carbanion and the adjacent oxygen) will dominate.

Based on $\ce{H2O}$ ($\mathrm{p}K_\mathrm{a} \approx 16$) vs $\ce{H2O2}$ ($\mathrm{p}K_\mathrm{a} \approx 11.5$), I would expect the inductive effect to be stronger, but I would like to check.


texts: Can aqua regia/royal water dissolve lead?

texts: As known aqua regia can't dissolve $\ce{Ag}$ because formation of $\ce{AgCl}$ precipitate. Similarly will aqua regia precipitate $\ce{Pb}$ as $\ce{PbCl2}$? OR It is not possible to observe this because aqua regia produce heat keeping solution warm ($\ce{PbCl2}$ is soluble in hot water).


texts: Electronegativity of elements on pauling scale

texts: When we say the electronegativity of Nitrogen is 3.04 ( on pauling scale ) what is the hybridisation of Nitrogen? Similarly for other elements?


texts: Can carboxylic acids be oxidised further?

texts:
I know that compounds like alcohols can be further oxidized to aldehydes (or ketones) and to carboxylic acids. But, is carboxylic acid the best oxidized form of a given compound?
What happens when carboxylic acids further reacts with oxidizing agents like $\ce{KMnO4}$?


texts:
I tried to create a suspension of EDTA powder in Glycerin with 1:1 ratio. I keep facing problem of EDTA sedimentation. I've tried other ratios also but this was the only one which formed least amount of sediment.
When I used coarse powder, the sediment formed within 24 hours but when finely ground powder was used, the same occurred but after 3 days. I even tried heating the powder & glycerin together on low & medium heat but EDTA sediment still forms but with varied time.
I'd like that the suspension remain consistent irrespective of how much time goes by.
I read on the internet that anti-settling agents (like xanthan gum & microfibrillated cellulose) can be used but I haven't tried that yet.
Can anyone please help & guide me?


texts:
My book gives me the following problem:
"A mixture of $125.0 g$ $\ce{N2}$ and $32.0 g$ $\ce{H2}$ reacts to $36.5 g$ $\ce{NH3}$. Calculate the efficiency."

My method to do this is - one I learned from my teacher, to put every given molecule's amount of substance (moles) in a table with 3 steps: start (S), gone (G)/formed (F) and rest (R).

$125g\:N_2 \leftrightarrow n=4.462$ moles

$32g\:\left(3\right)H_2\leftrightarrow n=16.13$ moles

\begin{matrix} &N_2&+&3H_2&\longrightarrow &2NH_3\\S&4.462&&16.13&&\\G&4.462&&13.386&F&8.924\\R&0&&2.74&&8.924\end{matrix}

($\rightarrow$ abundance of $H_2$)

Now, what is here the efficiency? Is it $\frac{36.5\:g}{8.924\:moles\cdot M_{NH_3}}\approx 24\%$?


texts: Equivalence point of titration of Sodium carbonate

texts:
The pH at the equivalence point of titration of $\ce{Na2CO3}$ solution with $\ce{HCl}$ is around 3.7, as shown in this titration curve:

At this point, the following reaction is completed:
$$\ce{NaHCO3 + HCl -> NaCl + H2O + CO2}$$
But considering the fact that $\ce{NaCl}$ is a neutral salt, shouldn't the pH be closer to 7? The $\ce{H2CO3}$ formed also decomposes to form $\ce{H2O + CO2}$, and shouldn't affect the pH either. Why then is the equivalence point at such a low pH value?


texts: After seeing this youtube video, I was left to wonder why to use a $30^\circ$ angle between the flask and the pipette when emptying it. I can imagine it is important to touch the flask with your pipette when emptying, because the liquid prefers being attached to a solid surface due to capillary forces. When just emptying it from above the flask droplets would remain at the tip of the pipette. But why the $30^\circ$ angle? Is this an important standard or just arbitrary?


texts: Why does chlorine have a higher boiling point than hydrogen chloride?

texts:
Chlorine has a boiling point of $238~\mathrm{K}$ while hydrogen chloride has a boiling point of $188~\mathrm{K}$.

Hydrogen chloride has dipole-dipole forces so I would expect it to have greater inter-molecular forces and thus a higher boiling point. However, since this is not the case, this must mean that chlorine has a greater intermolecular forces due to London dispersion forces.

But why?  I thought London dispersion forces were miniscule and only had a notable effect in large molecules. Shouldn't the dipole-dipole forces be way stronger than the London dispersion forces?


texts: Benzylic and allylic carbocation stability order

texts:
Most books I have read stop at this order :
Benzylic > Allylic > Tertiary > secondary > primary
However If I want to compare tertiary, secondary and primary benzylic and Allylic carbocations what will be their stability order?


texts: Is the correct configuration assigned to the given pair of geometrical isomers of 1,2-dichlorocyclopropane?

texts: I suppose that the configurations assigned are opposite as in the left isomer of 1,2-dichlorocyclopropane, the left chlorine atom is coming out of the plane of the paper while the other is going into the plane of paper. So it must be trans. Am I going wrong wrong somewhere?


texts: Does the Lewis acid have to match the halogen in electrophilic halogenation of benzene

texts: $\ce{FeBr3}$ catalyzes bromination and $\ce{AlCl3}$ chlorination. I'd like to know whether bromination and chlorination can be done in sequence without changing the catalyst? So - will using the $\ce{FeBr3}$ for chlorination and $\ce{AlCl3}$ for bromination work? Is it less efficient or slower or is there another reason?


texts: Appropriate container for storing/keeping chromic acid?

texts: I am planning to make chromic acid, however I the information for keeping chromic acid are conflicting. Can it be stored in a glass bottle even though it's used as a glass etchant? Also I saw some information that it's dangerous to keep it in plastic containers. What's the common practice?


texts: Finding rate constants for parallel reactions

texts:
A reactant $\ce{X}$ is converted into products $\ce{Y}$ and $\ce{Z}$
according to the following first order parallel reactions:

$\ce{X->[k_1]Y}$

$\ce{X->[k_2]Z}$

$\ce{[X]}$ has decreased from $\pu{1.00 M}$ at $t = 0$ to $\pu{0.549 M}$ after $\pu{10 min}$.
Calculate the rate constants $k_1$ and $k_2$, knowing that the yields of $\ce{Y}$ and $\ce{Z}$ obtained are $25.0$ and $\pu{75.0 mol\%}$, respectively.

So far, I have the ratio between $k_1$ and $k_2$ $=0.33$, which I found from the yield ratio but I'm unsure what to do with this ratio.

I also have derived the equation $[A] = [A]_0 \cdot e^{-(k_1+ k_2)t}$


texts: Flavor transference through the air and plastic bags

texts:
I am not sure if this is a chemistry question; however, I was wondering:

In my desk I have two plastic, zip-lock bags.  One contains cinnamon tea, the other contains nuts.

After about a week of these bags being next to each other, the flavor of the cinnamon somehow leached through both bags and now the nuts taste like cinnamon!

Is there a chemical explanation for this or isn't this a question of chemistry?


texts: Determining perovskite crystal structure

texts:
I've been reading that perovskite presents a sort of pseudocubic crystalline system, however it can be stretched and suffer modifications to become orthorhombic etc.

The thing is, if I consider it as cubic, it's sort of a combination between FCC and BCC, because it's an FCC with an atom in the center. I can't find a name for this sort of thing.

Can anyone help me out?


texts: Do ion-exchange resins soften water through a kinetic equilibrium process?

texts: I searched a lot for this and couldn't find any answers.  Is water softening a purely ratio-based equilibrium process, ie, more $\ce{Na+}$ cations on resin than there are $\ce{Ca^2+}$ cations in the water, causing most $\ce{Ca^2+}$ in solution to be displaced? Or do kinetic factors come into play, where at equilibrium $\ce{Ca^2+}$ cations will end up stuck on the resin over $\ce{Na+}$ cations because they are bigger and thus more restricted from leaving the resin due to steric reasons?


texts: Can two lone pairs in different orbitals make a chiral centre?

texts: Is it possible that if the two lone pairs in a molecule occupy different orbitals, then could this make the molecule chiral? What I mean is, suppose a carbon atom is attached to two different atoms and has two lone pairs in different orbitals, then could the carbon atom be considered chiral?


texts: Derivation of the isothermal Joule-Thomson coefficient

texts:
The definition of the Joule-Thomson effect is:

$$\mu=\left(\frac{\partial T}{\partial P}\right)_H$$

And this is defined in an isenthalpic process, i.e. $dH=0$.

My book shows the derivation of the isothermal Joule-Thomson coefficient ($\varphi$) using the cyclic rule:

$$\left(\frac{\partial T}{\partial P}\right)_H\times\left(\frac{\partial P}{\partial H}\right)_T\times\left(\frac{\partial H}{\partial T}\right)_P=-1$$

Using this cyclic rule,

$$\mu=\left(\frac{\partial T}{\partial P}\right)_H = -\frac{\left(\frac{\partial H}{\partial P}\right)_T}{\left(\frac{\partial H}{\partial T}\right)_P} = -\frac{\left(\frac{\partial H}{\partial P}\right)_T}{C_P}$$

And therefore

$$\left(\frac{\partial H}{\partial P}\right)_T = -\mu C_P = \varphi$$

I understand the mathematics of this derivation, but I don't understand it on a conceptual level.

$\mu$ was derived in an isenthalpic process, with $dH=0$. It owes it existence to the fact that there is no enthalpy change. So how can we now use this variable when $dH\neq 0$?

This question may be a more fundamental misunderstanding on my behalf of how thermodynamics equations are derived. Often I see an equation derived under the assumption that some variable is held constant, but then the equation applied when that variable is not constant any more. The above example is just one where I think this discrepancy is obvious.


texts: Using a modified Arrhenius plot to find activation energy

texts: I have a question on how to determine activation energy from a plot using the Arrhenius equation. I am working as an assistant with general chemistry II students and their lab is the iodination of acetone. I am familiar with using a plot of $\ln(k)$ vs $1/T$ to get the slope of $E_\mathrm{a}/R$ to solve for $E_\mathrm{a}$. Their lab manual though tells then to plot $\ln(t)$ vs $1/T$ to determine $E_\mathrm{a}$. I was wondering if anyone could shed some light on the derivation of this equation.


texts: Our teacher asked us if shaving cream is a solid, liquid, or gas. She didn't quite know herself.


texts: If absorbance is 0, what is the equilibrium constant?

texts: If the absorbance of something is 0, what is the equilibrium constant? In a reaction, the absorbance is 0, so the concentration of the product is 0. The concentration of one of the reactants is also 0. What does this say about the equilibrium constant? You would have to divide by 0, suggesting that keq doesnt exist for this reaction.


texts:
We know from Wikipedia that the combustion of rocket candy follow this equation :

$\ce{48 KNO3 + 5 C12H22O11 → 55 H2O + 36 CO2 + 24 K2CO3 + 24 N2}$

We can add small quantity of iron (III) oxide  ($\ce{Fe2O3}$) as a catalyst.

The new equation look like this :
$\ce{KNO3 + C12H22O11 + Fe2O3 -> H2O + CO2 + K2CO3 + N2 + ?}$

What product does the combustion of iron (III) oxide  produce ?


texts: What does it mean "polyester doesn't breathe"?

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Often people say buy a cotton shirt because cotton "breathes" but polyester doesn't. (i.e. it makes you hot sweaty).

What is the scientific meaning behind this? How does polyester trap the heat more than cotton?

I would have thought it would be the other way round. Is there some chemical explanation?


texts: Reduction of terephthalic acid to an alcohol (or phenol?)

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I want to convert terephthalic acid (TPA) to an alcohol (however I think the correct term would be "a phenol").

I've read that lithium tetrahydridoaluminate ($\ce{LiAlH4}$) can produce an alcohol from a carboxylic acid. And, according to Wikipedia, dicarboxylic acids (such as TPA) react around the same. So does $\ce{LiAlH4}$ reduce TPA to a phenol (or an other product)?


texts:
Why does benzoate show Friedel Crafts alkylation?

I know that benzoic acid does not show Friedel Crafts alkylation because the Lewis acid forms a bond with the lone pair of oxygen itself. So, shouldn't the same happen with benzoate as well? The oxygen in benzoate has a negative charge, which should make bond formation with the Lewis acid even easier. But my book states that it will show Friedel Crafts alkylation.


texts:
LSD (lysergic acid diethylamide) was formerly often referred to as ‘LSD-25’.
If it really is a (Albert Hofmann / Sandoz)'s code name (and not a combination of ‘LSD’ and usual LSD (Delysid) dosage numeral ‘25’ μg; see also Quora: What does the "25" in "LSD-25" mean?), are some other substances from the series LSD-1, LSD-2, … etc., being at a time probably a part of industrial secret, currently already known?
UPDATE
Summary
Identify at least one another Sandoz LSD-x, where x ≥ 1 and x ≠ 25 (with good sources or at least proven insider knowledge).


texts: What are simple applications of Monte Carlo simulations in chemistry, that can be done in Matlab?

texts: I am trying to learn simulation myself and I have installed Matlab on my machine for that purpose. In web I have gone through some of the basics of Monte Carlo simulation, but I am unable to find a simple Monte Carlo simulation experiment for chemistry. I am trying to simulate growth of a nano particle during a wet synthesis. I have tried searching research articles, but as I am new to simulations most of them I didn't understand. If possible can you explain a simple Monte Carlo experiment in chemistry, which can be done in Matlab. Is it possible to simulate the growth of nano particles using the Monte Carlo method?


texts: How much 'stronger' is water vapor than carbon dioxide, molecule-per-molecule, over the course of a day, in terms of global warming potential?

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I have read, many times, that water molecules are far more effective than CO2 molecules at trapping heat...
But, the 'relative G.W.P.' value of water vapor (or its 'radiative forcing') is not listed anywhere I can find, and the stated reason (if one is stated) is that water vapor has always been in the atmosphere in substantial amounts, of course, and if it has increased in prevalence recently it is because of increased CO2 levels, not the other way around....
So what is the amount of solar energy trapped/re-radiated by a water vapor molecule, over a very short time period, in direct comparison to a CO2 molecule?
I am very curious....