texts: What changes does zinc chloride undergo when ‘fusing’ on an atomic level? How does this influence reactivity?

texts:
I have been using a reaction with an organozincate starting material. This zincate is freshly prepared from zinc chloride and a Grignard reagent. The experimental procedure ‘handed down’ from more senior members of the lab include fusing the zinc chloride before use. ‘Fusing’ means:

heating under high vacuum with a heat gun until the salt melted
cooling the liquid down rapidly with the cold air stream of another heat gun to receive a glass-like solid

This is then dissolved in THF and the Grignard added.

In a recent group seminar I spoke about the trouble I had in achieving consistency with that reaction. Part of the resulting discussion revolved around the method of fusing and what I had been doing wrong. The PI noted how important it is for the fusing to be performed correctly as it influences the reactivity.

What actually happens to the zinc chloride during this process? My little understanding of inorganic solid-state chemistry leads me to believe that the initial crystals break down but the resolidified glass should essentially have the same structure. I am also at a loss how to explain any differences in reactivity following this method.

While it is not the most easy task to search for such references, the concept of fused zinc chloride does exist in the literature; the following two references use it in their experimental sections:

P. Dotta, A. Magistrato, U. Rothlisberger, P. S. Pregosin, A. Albinati, Organometallics 2002, 21, 3033–3041. DOI: 10.1021/om020314q. Synthesis of the ligand 4 on page 3040.
P. G. Gassman, J. G. Schaffhausen, J. Org. Chem. 1978, 43, 3214–3223. DOI: 10.1021/jo00410a024. Synthesis of compound 28 on page 3220.


texts: Different names for Fidaxomicin (OPT-80)?

texts: Is OPT in OPT-80 an abbreviation? If so, what is the full name?


texts: Difference between continuous and line spectrum of hydrogen

texts: The difference between a continuous and a line spectrum is well understood in that a clear cut boundary is present in the case of a line spectrum. When will continuous spectrum be obtained and when a line spectrum for example  in  hydrogen? What method can be used to observe either or both these spectra?


texts: Introductory chemistry book with calculus prerequisite

texts:
I understand that the policy here is that book requests are allowed, as long there is an effort to narrow it down. This question is similar to Can someone recommend me a book ( preferably written long ago) that includes all the details of high school chemistry?.

I am trying to find a book which tries to approach chemistry from the perspective of someone who has a higher-than-high-school-math background, i.e., they're proficient in calculus, but they aren't familiar with chemistry. Does any such book exist?

Reason why I'm asking for this is that mathematics undergraduate students, in my experience, get very little experience applying their problems outside of mathematical theory. Chemistry, in my years of tutoring and teaching, gets virtually no mention in calculus courses unless a math professor decides to discuss balancing equations using techniques in linear algebra. It has been years since I've seen high-school AP chemistry, but I recall rate laws being a consequence of integration, although this was never actually shown in AP chemistry. I made an effort, when I was a Calc. I TA, to show a class of mostly chemistry majors how the first-order rate law is derived from a differential equation.


texts: Alternatives to EDTA for calcium ion chelation

texts: Are there any $\ce{Ca^2+}$ chelating agents (other than EDTA) that are as good as EDTA in terms of binding calcium ions and effective in a pH range of $5$ to $9$?


texts:
Can clusters of an emulsion be emulsified into another emulsion?
If so is there any common product or natural substance that would have such a structure?

Finally is there a name for this? I looked around but the question gets drowned in all emulsion topics.


texts: General notation for one of the d-orbitals

texts: What is the general notation to represent the d-orbital with $l=2$, $m_l=0$, i.e. the orbital normally referred to as $\mathrm{d}_{z^2}$. To elaborate more, this orbital can be ordered in various ways in a crystal environment and can be written as: $\mathrm{d}_{3z^2-r^2}$, $\mathrm{d}_{3x^2-r^2}$ or $\mathrm{d}_{3y^2-r^2}$. So is there a general notation to represent all three, like $\mathrm{d}_{3A^2-r^2}$?


texts: ESI & MALDI Mass Spectrometry: particle mass vs. measurement error

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For MALDI or ESI mass spectrometry of large macromolecules (e.g. in the $\approx 100$ kDa to $\approx 10 - 100$ MDa mass range), I've always how measurement error scales with particle mass.  Not having any hands on experience with mass spetrometry, and calling anything build in the last 5 - 10 years "modern", are there any published tables of general rules of thumb for how measurement error scales with particle mass (the two must surely be positively correlated)?  If we're interested in measuring the mass of large intact nucleic acids or proteins, at what single-molecule particle masses does it make sense to use ESI or MALDI?

I'd guess that at higher mass ranges (e.g. in the MDa range) ESI might become preferable since it can produce multiply charged species, allowing for smaller $\frac{m}{z}$ ratios?


texts: How can the thermal conductivity of a binary gas mixture be estimated?

texts:
Recently, I am seeking for a simple but relatively accurate method to estimate the thermal conductivity of a binary gas mixture, say ethanol vapor + nitrogen. I assume the mixture as ideal gas.

The molar fraction and thermal conductivities of the components are known. The parameters for a try are: mole fraction of ethanol vapor: $x_A=0.2$, thermal conductivity of ethanol vapor and nitrogen are $k_A=0.016\ \mathrm{W/(m\,K)}$, $k_B=0.026\ \mathrm{W/(m\,K)}$, temperature of the mixture gas $T=330\ \mathrm{K}$, and the bulk pressure is $101\ \mathrm{kPa}$.

I really hope someone could give me a hint or point me to a classical reference.
Thank you in advance!


texts: In NMR Spectroscopy why use absorption and dispersion components of the FID spectrum rather than magnitude and phase?

texts: In chapter 4 of Dr James Keeler's book 'Understanding NMR spectroscopy' (http://www-keeler.ch.cam.ac.uk/lectures/Irvine/chapter4.pdf) he explains how to calculate the expected spectrum of a FID signal. In this chapter he analyzes the real and imaginary (absorption mode and dispersion mode) parts of the FID spectrum. This doesn't make sense to me. What is the physical interpretation of absorption mode and dispersion mode? Why not just rewrite the spectrum in polar coordinates and consider the magnitude and phase separately?


texts: Does plant material oxidize from 02 gas (air or solved in water) and/or oxygen in H20?

texts:
https://en.m.wikipedia.org/wiki/Curing_of_tobacco
Hi
This is my first time growing tobacco for fun, pleasent green at home, to make snuff for personal use and maybe save som money.
Ive been reading a bit on wiki, it says oxidization is what makes tobacco cure/age/mature take out the harsh.
Im wondering about if the oxidization of caratenoids and chlorophyll in tobacco curing is from O2 in air (or solved in water) and/or from O in H2O itself?
From what i remember, from school and various archeology programs on tv, wood in sea bed with no O2 solved in it doesnt rot but metals will rust. ?
At what relative humidity at room temperature will tobacco leaves sealed in a jar (in fall and winter the relative humidity in my apartment will drop too much for curing tobacco, i guess) cause them to cure? If air is required, how much?
/Johan


texts:
In many textbooks and chemistry curricula, we can see the description of large molecules (particularly in the discussion of hydrocarbons and other nonpolar compounds) as having "entanglement." However, I think the term is misleading, since the molecules don't really act like tangled shoelaces or two strings pulling against each other while interlocked. Can we try to clarify what actually occurs that we describe as entanglement?

Some things I think may happen:

The molecules are very large, and thus have many sites for IMFs, leading to high viscosity.
By way of this size, the molecules are much harder pressed for movement and so take a while to move (the distinction is that in the first example the increased size begets more IMFs whereas the second causes "entanglement" just by the bulky molecules' shifting past each other).


texts: Are the odours added to natural gas completely flammable?

texts:
I live in Australia, where both electricity and natural gas are common forms of household energy. An odour is added to the natural gas as a safety precaution since it is otherwise almost undetectable. I haven't been able to find what gas/mixture of gases is used in Australia, with all the sites I've checked just saying "an additive" or "an eggy smell".

The Wikipedia article on natural gas says that both tert-Butylthiol and tetrahydrothiophene can be used as an additive, and the article on tetrahydrothiophene says:

  It is also used as an odorant for natural gas, usually in mixtures containing tert-butylthiol.

Whenever I've used natural gas (i.e. burning it for heating or cooking) I've noticed that there is no smell afterwards. Are all the additives completely flammable? Presumably, their combustion products are odourless, but I haven't been able to find any information on that either.


texts: Method of deriving some properties or possible method of synthesis of a specific monomer

texts:
This is kind of like two questions but since they're related I have put them together.

Consider a monomer under a hopefully anatomically correct name 'Phenyl Carbolithia Divinylene Oxide [$\ce{C11H9LiO4}$] (For ease of understanding.)

Would it be possible for me to find or estimate some basic properties (physical and chemical)? Or the 3D structure of the molecule (As opposed to the one I plotted, which is based on my estimation of dipole with minimal reasoning.)

By separating the molecules into parts:

Lithonate (Lithium Carbonate)
Benzene (Phenyl group)
Ethylene (Vinylene group)
Divinyl Ether

Perhaps now it is possible to make some predictions based on some functional groups? (Such as ether.)

Though theoretical chemistry has shown that such achievement in predicting a physical structure is unlikely, I am wondering if anyone would know specific properties of this molecule and the way they have deduced it in which I haven't consider.

The second part of the question may lead to the solution for the first part, by synthesizing such molecule.

My humble attempt at theorizing the chemical synthesis with my limited knowledge on the subject is based on condensation polymer. Perhaps having the separate parts of molecules mention previously dehydrated to form a chain, the molecule may be created if a similar polymer is formed except to have the carbon-oxygen backbone chain to form a ring instead.

I also have a slight inquiry on whether it is possible for the double bond to exist in this monomer; and whether my nomenclature for this substance is anatomically correct.


texts: When is a ligand strong field or weak field?

texts:
I have seen many examples where a strong field ligand is written for a particular ion .

For example, we have $\ce{Co(H2O)6^3+}$. What is the hybridization of $\ce{Co^{3+}}$? Now, we know $\ce{H2O}$ comes later in the spectrochemical series, thus it should be considered a weak field ligand. But for $\ce{Co^3+}$, $\ce{H2O}$ acts as a strong field ligand and pairs up the electron causing the hybridization to be d2sp3. This doesn't make sense. If we can see that a ligand is weak with respect to the spectrochemical series and it turns out that its not just for a particular ion, why is it so?

Also, another example is where $\ce{NH3}$ is supposed to be a strong field ligand but comes out to be a weak field ligand just for a particular ion.

Why does this happen? How do I know when to consider a ligand strong or weak?


texts: How can diesel fuel produce less carbon monoxide but more carbon particulates?

texts:
My guess at why diesel produces less carbon monoxide is that more heat is required for combustion of diesel fuel, so there is less incomplete combustion. Therefore rather than carbon monoxide being formed and released, the ability to completely combust means that carbon dioxide is often formed instead. Correct me if I'm wrong.

However, a risk of diesel fuel is that more carbon particulates are produced. But surely this is just a contradiction, because carbon particulates are a result of a lack of oxygen supply and incomplete combustion. Surely if there is enough complete combustion to form carbon dioxide over carbon monoxide, then there is a high enough oxygen supply and temperature to stop carbon particulates forming?


texts: What is a typical monolayer formation time for liquid phase adsorbate on a solid surface?

texts:
Let's say a solid is submerged in a solution of species with functional groups and a self-assembled monolayer is forming. What are the typical time scales for the formation of a continuous monolayer? (seconds, minutes, days..?)

 (source)

For an adsorbate in gaseous phase and high vacuum, a rough approximation on Wikipedia is ~1 sec.


texts:
I was wondering what salts of gold are soluble and which are insoluble. From what I understand, silver is soluble as silver nitrate but insoluble as most other common salts like chlorides and sulphates. How does this work with gold? I was also wondering if there are any rules for solubility of salts, or whether there is some explanation for the solubility that would help in guessing the solubility of a salt?

I started thinking about this because of a question I came across in which there was a mixture of gold, silver and copper to which hot concentrated nitric acid was added, and an undissolved residue of given mass remained. Then $\ce{HCl}$ was added and more precipitate was formed. The question asked you to find the percentage by mass of gold, silver and copper. Judging by the general solubility trend of these metals, I'm guessing the first precipitate was gold and the second silver, but I was also wondering if there are some solubility rules...


texts:
I am trying to find the mass density $\rho$ of plutonium dioxide, $\ce{PuO2}$. I could calculate it, but the mass density of oxygen found in the literature is the density of gas oxygen.

So I was wondering where can one find mass densities for compounds that come from experimental measurements?


texts: Do all adiabatic processes involve a change in temperature?

texts:
I learnt that adiabatic processes involve no heat exchange between the system and the environment. Does this mean that all adiabatic processes involve some changes in temperature then?

Thanks a lot!


texts: Do all supercritical fluids dissolve the same substances?

texts: In the case of regular fluids, polar solvents dissolve polar molecules and nonpolar solvents dissolve nonpolar molecules. Is there something analogous for supercritical fluids? In other words, does the shape of the supercritical fluid molecule affect what it dissolves, or do all supercritical fluids dissolve the same set of substances?


texts: What happens in an acid and metal reaction where the acid is twice as concentrated and the metal twice as much in quantity?

texts:
Experiment A

3cm metal

0.5M acid

5 degrees temperature change

Experiment B

6cm metal

1M acid

How much would the temperature change be, and how much faster or slower would the reaction take place in?

I thought the answer would be either "the same" or "4x as much". I don't exactly understand the reaction yet; would the doubling of each material make the reaction 4x stronger (2x2), or would they cancel each other out?

Of course, it might've been something else I haven't thought of, too.


texts: Why do substances ionise in water to turn into charged species? Wouldn't they prefer to stay as uncharged molecules?

texts:
Wouldn't this be more stable if they stayed as neutral molecules?

I've learnt that they will seek to reach the ratio of $[A]^a[B]^b/[C]^c$ that matches the $\ce{Ka}$ or $\ce{Kb}$ value.

But I do not understand why they wouldn't prefer to stay as uncharged molecules as I thought ions are unstable compared to neutral molecules?


texts: Is the Hartree-Fock determinant always the minimum energy single Slater determinant solution to a molecular Hamiltonian?

texts:
Is it always true that the Hartree-Fock slater determinant is the minimum energy single slater determinant solution to a given molecular Hamiltonian $H$?
By construction, any determinant $|\chi_{i_1}\ldots \chi_{i_N}\rangle$ where the $\chi_{i_j}$ are distinct solutions of the Hartree-Fock equation $f(x) \chi(x) = \epsilon_i \chi(x)$ will have stationary energy $\langle \chi_{i_1}\ldots \chi_{i_N} | H |\chi_{i_1}\ldots \chi_{i_N}\rangle$ (where stationarity is with respect to perturbing the orbitals). The Hartree-Fock slater determinant $|\Phi_0\rangle =|\chi_1\ldots\chi_N\rangle$ is constructed by choosing the lowest $N$ energy solutions of the Hartree-Fock equation.
Now, $|\chi_{i_1}\ldots \chi_{i_N}\rangle$ is an eigenstate of the Hartree-Fock Hamiltonian $H^{HF}$ with energy $\sum_{i=1}^N \epsilon_{i_j}$, so constructing $|\Phi_0\rangle$ from the $N$ lowest energy solutions of the HF equation clearly minimizes the energy of $H^{HF}$.  But the molecular Hamiltonian $H$ is given by
$$H = H^{HF} + \sum_{i=1}^N\sum_{j>i}^N \frac{1}{r_{ij}} - \sum_{i=1}^N v^{HF}(i)$$
where $v^{HF}$ is the HF potential.  This satisfies
$$\langle{\Phi_0}|H|\Phi_0\rangle = \sum_{i=1}^N \epsilon_i - \frac{1}{2}\sum_{i=1}^N \sum_{j=1}^N \langle ij|\,|ij\rangle $$
where
$$\langle ij|\,|ij\rangle:=\int dx_1 dx_2 \chi_i^*(x_1)\chi_j^*(x_2)\frac{1}{r_{12}}(\chi_i(x_1)\chi_j(x_2) - \chi_j(x_1)\chi_i(x_2))$$
Due to the $\langle ij|\,|ij\rangle$ term, it is not clear to me that constructing $\Phi_0$ from the $N$ lowest energy solutions of the HF equations still results in the lowest energy single slater determinant for $H$.  An excited determinant would have a higher energy contribution to the $\sum_i \epsilon_i$ term, but could this is offset by a greater deduction from the $\langle ij|\,|ij\rangle$ term?


texts: What is the reaction order of a reaction?

texts:
Here's is what I understand so far and the following is referenced directly from UNSW CHEM1061 lecture notes by Professor Pall Thordarson:

order of the reaction SHOULD be equal to the number of molecules of that reactant involved in each collision ( however this is not always the case)
it is only possible to predict the order of a reaction is it occurs in a single step (elementary reactions)
reaction order is experimentally derived from rate equation

so I understand all of the above but what I fail to fully comprehend is that actual DEFINITION of 'reaction order' what is it in it's entirety, what does it's value represent if it only sometimes correlates with molecularity (no. of molecules which react in an elementary reaction) ? If someone can answer this question could they please provide a qualitative answer that explains the value conceptually? Or is it just a value to relate concentration to reaction rate? that helps us work out more information?


texts:
The value of $K_p$ for the reaction

$$\ce{Br2(l) + Cl2(g) <=> 2BrCl(g)}$$

is $\pu{1 atm}$. At equilibrium in a closed container partial pressure of $\ce{BrCl}$ gas is $\pu{0.1 atm}$ and at this temperature the vapour pressure of $\ce{Br2(l)}$ is also $\pu{0.1 atm}$. Then what minimum moles of $\ce{Br2(l)}$ to be added to $\pu{1 mol}$ of $\ce{Cl2}$ initially to get the equilibrium mixture from above?

In this question should I include the vapour pressure of $\ce{Br2}$ in calculating $K_p$ or not?


texts: How much steric hindrance does a phenyl group offer?

texts: I've come across a question in my revision in which I am asked to compare the steric hindrance provided by a number of substituents. Those relating to phenyl are ranked relatively low, despite it being what I thought was a rather large substituent. Is this due to the planarity of the ring, or is it just much smaller than I originally thought; does a tertiary alkyl substituent provide more steric hindrance because it is larger, or because it is spread in all directions?


texts: How do metal's density affects the corrosion rate?

texts: Based on different formula that can be used to compute the corrosion rate of metals, all of them involves weight loss, time, surface area, and density. I thought that the weight loss, surface are, and time should definitely be considered. But, I got confused about the relevance of the metal's density. How does that affects metal's corrosion?


texts: How would one determine the yield of primary vs. secondary hydrohalogenation addition products?

texts:
For example, if I was to perform the following reaction:

$\ce{CH3CHCH2 + HBr -> CH3CHBrCH3 + CH3CH2CH2Br}$

How would I quantitatively determine the relative yield of the primary and secondary alkyl halides?

Would IR or UV/Vis spectrscopy be able to differentiate between them, or would I have to utilize reactions such as substitution with hydroxyl then oxidation to form ketones and carboxylic acids to differentiate between the two?


texts: Precise explanation of macrocyclic effect

texts:
In most of the books, the reason of macrocyclic effect is given that It occurs due to preorganised structure of macro-cyclic ligand.
But a proper explanation of these two particular examples isn't given anywhere (even in the book from I've read it).

I've come up with the following explanation -

Cyclam has just a proper size for bonding, therefore it is stable due to its Bond Enthalpy, But it's a big molecule so It should have more Degree of freedom. For a proper bonding, it has to be in some particular conformation out of many other conformations. So it is an entropically disfavored molecule.

But in case of Cyclen, Its ring is small so its bonding isn't that good as compared to cyclam but since it is a smaller molecule so there should be less no. of possible conformation, So statistically achieving that particular conformation isn't that hard for Cyclen.

I don't know why? But it's not satisfying me, am I making some mistake (overlooking something important)? Or Is it correct?


texts: Which DFT functional is best for predicting macroscopic properties of molecular liquids?

texts:
Which DFT functional (KS-DFT, to be more specific) performs best at predicting macroscopic properties (density, surface tension, boiling point, relative permittivity etc.) of molecular liquids (molecular as opposed to ionic liquids or molten metals)? I'm interested in both water and commonly used organic solvents.

Or, alternatively, if there is no definitive answer: Is there at least a set of functionals which are known to perform poorly in that respect, functionals that I should not use?


texts: Why do post-Hartree-Fock methods fail to predict the direction of the dipole moment of carbon monoxide?


texts: Why does the unstabilised Wittig reaction selectively form cis alkenes?

texts:
This question is meant for a simple unstabilised ylide.

The mechanism of the Wittig reaction, as given on ChemTube3d, involves a concerted formation of the oxaphosphetane (this is generally favoured over the traditional stepwise mechanism with betaine formation):

Here the puckered transition state has been clearly shown but involves the direct formation of the oxaphosphetane (without any betaine intermediate). In this transition state, the two possibilities are for the methyl groups to be either cis or trans to each other. Surely the transition state with the methyl groups trans to each other will be more stable. Doesn't this support formation of the trans product?


texts: How to find the highest and lowest oxidation state of transitional metal

texts:
My teacher taught me the formulas 'nS' and 'nS+(n-1)d' to find the highest and lowest oxidation state of transition elements. He gave the example of $\ce{Mn}$ and showed that the numbers were +2 and +7. But I did not understand it. So can please you give me
a good explanation.


texts: What is the identity of the unknown compound using GCMS and NMR?

texts:
I've been asked to identify an unknown compound by performing several analytical techniques on it.

The compound was a white powder and had a boiling point of 65 degrees celsius.
I have the GC mass spectrum as well as both Carbon-13 and Proton NMR spectra (note that the compound was dissolved in chloroform for NMR analysis).
So far I think it contains an aromatic ring because of the chemical shifts for the NMR spectra but that's all I have so far.

These are the images of the spectra (Fig 1. GC and Mass spectrum, Fig 2. Proton NMR spectrum, Fig 3. Zoomed in Proton NMR spectrum, Fig 4. Carbon NMR spectrum, Fig. 5 Zoomed in Carbon NMR spectrum):


texts: Cis/trans with alkene substituents on cycloalkanes

texts:
My chemistry book is saying that the double bond indicated by the red arrow can generate cis/trans isomers:

I don't understand how this can be so, as you need to use E/Z priority rules in this case. If you go by the rule for cis/trans of finding the longest carbon chain containing the double bond, and seeing if the chain ends up on the opposite or same side of the bond, you find that by going around the ring, both options of cis or trans have the same length.

Am I missing something here, or is this a case where you really should be using E/Z, not cis/trans?


texts: How to correctly write the condensed formula for salicylic acid

texts:
I am struggling to find the right way to write the condensed formula for salicylic acid

Some people say CHCHCHCHC(OH)C(COOH)
Or (CH)4C(OH)C(COOH)

Others say C6H4(OH)COOH (which doesn't seem to make sense since it looks to me like it could represent many isomers and not just one molecule like a condensed formula is supposed to)

Which (if any) is correct?


texts: Chemical Equilibrium - Why does changing the temperature shift the equilibrium?

texts:
I know that raising the temperature in a reversible chemical reaction causes the equilibrium to shift to the endothermic side.

I know that $\Delta G = \Delta H - T \Delta S$ but I don't know how to put them together to show why the equilibrium would shift.


texts: How to find and use the Clausius-Clapeyron equation

texts:
I know how to get the equation from the Clapeyron equation but I have a question regarding a the integration along a phase boundary and a small step in the derivation that I will make clear when I reach that step. Firstly, the Clapeyron equation:

$$\frac{\mathrm{d}p}{\mathrm{d}T}=\frac{\Delta S}{\Delta V}$$

Or alternatively, by recognizing that $\Delta G=0$ when two phases are in equilibrium; $\Delta G =\Delta H - T\Delta S$ can be rearranged to give:

$$\Delta S = \frac{\Delta H}{T}$$

Substituting this into to the the first equation gives:

$$\frac{\mathrm{d}p}{\mathrm{d}T}=\frac{\Delta H}{T\Delta V}$$

At a solid/gas or liquid/gas phase phase boundary, it is a reasonable to approximate that $\Delta V \approx V_{m,\text{gas}}$ as $\Delta V = V_{m,\text{gas}}-V_{m,\text{condensed}}$ since $V_{m,\text{gas}} \gg V_{m,\text{condensed}}$

Consequently, using the equation of state for a perfect gas and substituting for $\Delta V$ in the second form of the Clapeyron equation, the following result is obtained:

$$\frac1p \frac{\mathrm{d}p}{\mathrm{d}T}=\frac{\mathrm{d}\ln p}{\mathrm{d}T}=\frac{\Delta H}{RT^2}$$

However, why is $\frac1p \frac{\mathrm{d}p}{\mathrm{d}T}=\frac{\mathrm{d}\ln p}{\mathrm{d}T}$?

The following step is the step that I don’t understand In my lecture handout this step is shown as:

$$\int_{p_1}^{p_2}\frac1p\mathrm{d}p=\int_{T_1}^{T_2}\frac{\Delta H}{RT^2}\mathrm{d}T$$

Why can the left hand side be integrated with respect to $p$, yet the right hand side be integrated with respect to $T$. I cannot make sense of this. Other instances in thermodynamics when integration is used like this, both sides are integrated with respect to the same variable. For example, finding how $H$ varies with $p$. I will quickly go through what I mean without much verbal explanation:

$$\mathrm{d}H=T\mathrm{d}S+V\mathrm{d}p=\left(\frac{\partial H}{\partial S}\right)_p \mathrm{d}S+\left(\frac{\partial H}{\partial p}\right)_S \mathrm{d}p$$

Consequently, for one mole of a perfect gas:

$$V=\left(\frac{\partial H}{\partial p}\right)_S=\frac{RT}p$$

Thus:

$$\int_{p_1}^{p_2}\left(\frac{\partial H}{\partial p}\right)_S\mathrm{d}p=\int_{p_1}^{p_2}\frac{RT}p\mathrm{d}p$$

Since $\left(\frac{\partial H}{\partial p}\right)_S\mathrm{d}p=\mathrm{d}H$ at a constant $T$ (I think this is right – please clarify)

$$\int_{p_1}^{p_2}\mathrm{d}H=RT\int_{p_1}^{p_2}\frac{1}p\mathrm{d}p$$

This can obviously be integrated quite easily but this only illustrates my point regarding the variable that the integration is carried out with respect to. Surely it must be the same on both the RHS and the LHS of the equation?


texts:
In this YouTube video from Cody's Lab, Cody claims that heavy water tastes sweet.

He does some fairly convincing comparisons but still expresses a little doubt that the effect is real.

Has this been studied by others? Is the effect verified and if so, what possible explanations exist?


texts:
Read Orthocresol's answer here first: What is the difference between "molecular mass", "average atomic mass" and "molar mass"?

Orthocresol, in his answer, says that atomic mass is the weighted average mass of the atoms of an element and molecular mass is the mass of the molecule of an element/ compound obtained by adding the atomic masses of the constituent element's/ elements' atoms. Both atomic mass and molecular mass have the units of mass which may be kilograms, grams, daltons or a.m.u.

Relative atomic mass/ atomic weight is the ratio between the atomic mass of an atom and 1/12th of the atomic mass of a C-12 atom and similarly, relative molecular mass/molecular weight is the ratio of the molecular mass of a molecule and 1/12th of the atomic mass of a C-12 atom. Both R.A.M. and R.M.M are unitless since they are the ratio of two physical quantities which have the units of mass.

My Question: Atomic masses and molecular masses expressed in a.m.u or u have the same numerical value as R.A.M. and R.M.M respectively. What is the point of having R.A.M and R.M.M?


texts: Why is there no salt bridge in electrolytic cell?

texts:
I was just wondering why is there no salt bridge in electrolytic cell? It is said that electrodes are in a common electrolyte solution without salt bridge.
However, when I searched the image of the difference between electrolytic cell and galvanic cell, the salt bridge are in both of the cells.

The reference website http://mcat-review.org/electrochemistry.php


texts: Find empirical formula when individual masses are known

texts:
I'd like to illustrate my question with an example:

Imagine nickel reacts with fluoride and you start with $0.766\ \mathrm{g}$ of nickel, an unknown amount of fluoride and you end with $1.261\ \mathrm{g}$ of nickelfluoride. The mass of fluoride in the end must then be $1.261\ \mathrm{g} - 0.766\ \mathrm{g} = 0.495\ \mathrm{g}$.

So, in the end there's $0.013$ moles of nickel and $0.026$ moles of fluoride. Now the question is, what is the empirical formula for nickel fluoride? ($\small\ce{NiF2}$). I see that for every mole of nickel you need $2$ moles of fluoride but then why is the empirical formula $\small\ce{Ni2F4}$ incorrect?


texts: Maximum metal-metal distance for antiferromagnetic coupling

texts: Imagine a transition metal complex with multiple open-shell transition metal cations. If the metals are relatively close in distance, it is possible that antiferromagnetic coupling will occur between the metals. However, at approximately what distance does ferromagnetic vs. antiferromagnetic alignment of spins become isoenergetic due to negligible coupling between the metals? To provide some context, I'm asking about this in the context of density functional theory calculations. To make sure we're on the same page, let's call two magnetic configurations "isoenergetic" if the energies are, say, within ~1 kJ/mol or so.


texts: Explaining base peak for but-3-en-1-ol mass spectrum?

texts:
The mass spectrum for but-3-en-1-ol shows 42 as the base peak, but I don't know how this fragment ion is generated.
I would expect the most favorable fragmentation to occur between C1 and C2, but neither the allylic nor the hydroxymethyl fragments would have a mass of 42.


texts: Using baking soda paste (alkaline) to "neutralize" honeybee venom (acidic). Is this scientifically sound?

texts:
I recall reading (courtesy: my 9th grade Chemistry text-book, chapter Acids, Bases and Salts), something along the lines of:

  Bee venom is acidic. This is why the area of skin (stung by a bee) is treated (first-aid) by the topical application of a sodium bicarbonate paste. This method works by neutralization of the acidic venom.

The problems with this theory? I see three:

Firstly,

A honeybee's stinger can grow to be as long as 3mm. If bee venom were acidic, then how would the baking-soda paste neutralize it (entirely) by simply applying it on the surface?

Secondly,

Wikipedia provides the composition of honeybee venom;

  Melittin

  Apamin

  Adolapin

  Phospholipase A2

  Hyaluronidase

  Histamine

  Dopamine and Noradrenaline

  Tertiapin

As far as I know...none of these are actual acids, instead, they're pretty much all proteins. Which appears to seriously contradict the popular "Bee venom is acidic" notion.

Thirdly,

Some sources (online) suggest that application of vinegar (which is acidic) also relieves the pain. Additionally, even meat tenderizers (proteases), toothpaste and wet aspirin tablets seem to do the trick.

So I'll break up my question into two bits (to hopefully, make it easier to answer):

1) Is honeybee venom acidic? If so, what substance present in it is responsible for the "acidic" nature of the venom?

2) Why does applying baking-soda (paste) relieve the pain? Does it somehow denature/"neutralize" the venom?


texts: Ring contraction in benzilic rearrangement

texts:
Wikipedia says that,

  Benzilic acid rearrangement occurs with ring contraction when used on cyclic diketones.

But gave no explanation, can you please elaborate on this with some mechanism. One such reaction I found here, why ring contraction taking place?


texts: What is the role of imidazole in the Appel Reaction with iodine (I2)? Why are other bases not used?

texts:
I presume the role is to soak up the HI that is formed. Why not other bases such as triethylamine? Is this because the quaternary ammonium salt could be formed? Would other non-nucleophilic or inorganic bases work (for instance, k2co3 or DBU)?
http://www.commonorganicchemistry.com/Rxn_Pages/Alcohol_to_Halide/Iodide/Appel.htm


texts: Is there an alternative to the half-reaction method to solving red-ox reactions?

texts:
The equation for the reaction between a permanganate and iron(II) ions in acidic solution is:

$\text{MnO}_4^- + \text{Fe}^{2+} \longrightarrow \text{Fe}^{3+} + \text{Mn}^{2+}$

My book, as well as a certain equation balancer, shows that the answer is:

$5\text{Fe}^{2+} + \text{MnO}_4^-  8\text H^+ \longrightarrow 5\text{Fe}^{3+} + \text{Mn}^{2+} + 4\text H_2\text O$

They check the charges to ensure that it is indeed balanced. My book says that:

$5(2+) + (1-) + 8(1+) = 17+$

$5(3+) + (2+) + 0 = 17+$

And voila, they must be therefore balanced. However, there must be more than one way to balance such a reaction, like many problems. Is there a different, perhaps a more interesting, method than the half-reaction method for balancing this reaction and others?


texts:
You add $100.0\ \mathrm g$ of water at $55.0\ \mathrm{^\circ C}$ to $100.0\ \mathrm g$ of ice at $0.00\ \mathrm{^\circ C}$.  Some of the ice melts and cools the water to $0.00\ \mathrm{^\circ C}$.  When thermal equilibrium is established at $0.00\ \mathrm{^\circ C}$, what mass of ice has melted?
  $\Delta H$ of fusion for water is $333\ \mathrm{J/g}$.

My question is I got a negative for $q$.  Would this change to a positive because you need heat to melt the ice?  I no you can't have a negative. So I am not sure if it should be a neg or a positive

$q = m \times \text{specific heat} \times (T_\text{final} - T_\text{initial})$
specific heat of water is $4.186$ (should memorize or on a chart)
$q= 100\ \mathrm g \times 4.186\ \mathrm J \times (0 -55) = -23\,023\ \mathrm J$

mass ice × heat of fusion
$q= m \times H_\text{fusion}$
$-23\,023\ \mathrm J = m \times 333\ \mathrm{J/g} = 69.12\ \mathrm g$


texts: Buffer capacity of different types of milk

texts:
Currently I am tasked with designing an experiment that that I will have to perform in 2-4 weeks, but I don't have to decide on on a topic soon. I was thinking of performing an acidometric titration (most likely with hydrochloric acid) of different types of milk such as skim, organic, fat free and from it make a $\mathrm{pH}$ curve. From here I would see how these different types of milk acted as buffers relative to each other, by analyzing their buffer regions in the $\mathrm{pH}$ curve.

I have heard that milk can act as a buffer, but I cannot find information about what buffers regulate the $\mathrm{pH}$ the most.
I would greatly appreciate if any of you could share your knowledge or some sources about buffers constitute milk.


texts: Why is the aqueous solution of KMnO4 slightly basic?

texts:
This is in the context of the various changes in oxidation state the permangananate ion can undergo with the variation of the pH of the medium. Besides the cases of strongly basic and strongly acidic media, the case for neutral media (with reduction to $\ce{MnO2}$) in my notes has a footnote; that this medium is in fact slightly alkaline, due to it being a solution of $\ce{KMnO4}$.
I tried to reason this out. It looks like $$\ce{K+ + MnO4- + H2O -> K+ + OH- + HMnO4}$$ is how it works out.
A quick google search establishes the pKa of HMnO4 to be -2.25. So it makes a pretty good acid in comparison to water.
Thing is, in that case, the product side should have an $\ce{H2O}$ instead of the constituent ions, with the potassium permanganate dissociated. That means the solution's neutral. Which apparently it isn't, going with my notes.
Where did I mess up here?


texts: Sulfuric acid fumes from cleaning shower drain

texts:
This morning a workman came by to my newly rented property to fix a few things, among which a slightly blocked bathtub drain.

He let some mild water run continuously and he poured down a chemical, and it wasn't before I saw a huge vapor coming out and an intense boiling-like sound, I realized something was wrong. Basically he let down an entire bottle of >95% sulfuric acid down the drain just like that, without even wearing safety goggles or gloves. A pungent odor emanated through the whole flat and I had to open every window (he hadn't advised to open them beforehand).

Now, I don't have much experience with chemicals of this sort, so here are my questions:

Did I inhale toxic fumes?
What should I do to make the bathroom/shower usable again? I noticed that the mirror and several water tiles that are not in the close proximity of the drain but are on the way to the nearest window opening, show condensation streaks, such as those left by drops of water that run down. They were definitely not there before. Is that condensed sulfuric acid vapor? Do I need to clean with a sodium bicarbonate solution?
Needless to say, I also had towels, toothbrushes, and other items in the room, do I need to take any precaution before using them (cleaning, rinsing, etc?).

In short, how do I clean up this mess?


texts: Predicting the product of a hydrogenation reaction

texts:
The question is to predict the nature of the product(s) of the above reaction, that is if the product(s) form a racemic mixture, meso, diasteromers, or are structural isomers.

I am aware of the fact that addition of $\ce{H2}$ is a syn addition. So it should form a meso compound. However the answer key gives it as a mixture of diastereomers. I am not quite sure if the reaction is strictly selective and some anti products are also formed.


texts: How do I perform a gravimetric analysis of Portland cement?

texts:
To determine the silica ($\ce{SiO2}$) content in Portland cement by gravimetric analysis it is digested in $\ce{HCl}$ and the silica residue is eventually measured.

The chief constituents are $\ce{Ca2SiO4}$ (or $\ce{2CaO.SiO2}$), $\ce{4CaO.Al2O3.Fe2O3}$, $\ce{Ca3(AlO3)2}$ (or $\ce{3CaO.Al2O3}$), and $\ce{CaSiO3}$ (or $\ce{CaO.SiO2}$). Gypsum is also present. What species are present in solution after the $\ce{HCl}$ has reacted with the cement? I assume $\ce{CaCl2}$ and $\ce{H2O}$ would be present, but would $\ce{AlCl3}$ also form? How would I approach this problem?


texts: How to determine the equivalent weight of carbon dioxide correctly?

texts:
I just started learning about equivalent weight and encountered this solved example.

  Problem Statement:

  $4.215~\mathrm{g}$ of a metallic carbonate was heated in a hard glass tube and the $\ce{CO2}$ evolved was found to measure $1336~\mathrm{mL}$ at $27~^\circ\mathrm{C}$ and $700~\mathrm{mmHg}$ of pressure. What is the equivalent weight of the metal?

My attempt:

First of all lets find the volume occupied by $\ce{CO2}$ at NTP.

We know,
$$\frac{P_1 V_1}{T_1}=\frac{P_2V_2}{T_2}$$

Now, as it is given that
$$\begin{align}
&P_1 = 700~\mathrm{mmHg}\\
&V_1 = 1336~\mathrm{mL} = 1.336~\mathrm{L}\\
&T_1 = 27~^\circ\mathrm{C} = 300~\mathrm{K}\\
&P_2 = 760~\mathrm{mmHg}\\
&T_2 = 273~\mathrm{K}
\end{align}$$

Hence, $$V_2=\frac{P_1\times V_1\times T_2}{T_1\times P_2}=\frac{700\times 1.336\times 273}{300\times 760}=1.12~\mathrm{L}$$

Also, according to the law of equivalence, we get

$$\text{equivalents of metal carbonate} = \text{equivalents of }\ce{CO2}$$

Now comes the part where I am really stuck, i.e. how to determine the volume occupied by $1$ equivalent of $\ce{CO2}$.

I started with finding the equivalent weight of $\ce{CO2}$ by considering the reaction of carbonation of water which produces $\ce{H2CO3}$
$$\ce{CO2 + H2O -> H2CO3}$$
As we know the equivalent weight of $\ce{H2CO3}$ is $\frac{M}{2}$ because it has a basicity of $2$.

Hence, according to the law of equivalence,

$$\text{Equivalent of }\ce{CO2} = \text{Equivalent of }\ce{H2CO3}$$
which gives us the equivalent weight of $\ce{CO2}$ to be $22~\mathrm{g/equivalent}$. Hence, the equivalent volume of $\ce{CO2}$ at NTP is $11.2~\mathrm{L}$

Now consider this another method.

The equivalent weight of $\ce{C}$ in $\ce{CO2}$ is $3~\mathrm{g/equivalent}$ as $1 \ce{C}$ combines with $4$ equivalents of $\ce{O}$ to form $\ce{CO2}$, hence we get the equivalent weight of $\ce{CO2}$ as $3+2\times8=19\text{ g/equivalent}$ which is super weird.

My deal with the question:

What am I doing wrong in the second method for finding the equivalent weight of $\ce{CO2}$ and if you wanna know why I added the equivalent weights of the elements was because I had read that for finding the equivalent weight of an electrolyte we add the equivalent weights of the cations and anions. Hence, I tested this method of finding the equivalent weight on $\ce{SO4^2-}$.

Here is my attempt of finding the equivalent weight of $\ce{SO4^2-}$ using the method for electrolytes. We know that equivalent weight of $\ce{S}$ is $\frac{32}{2}=16$ and that of $\ce{O}$ is $8$, so we have

$$\text{Eq. } \ce{SO4^2-} = \text{Eq. }\ce{S} + 4 \times \text{Eq. }\ce{O} = 16 + 32 = 48~\mathrm{g/equivalent}$$

For those who are attempting to solve the problem:-

The solution provided by the book is as follows:-

   Volume of $\ce{CO2}$ at NTP=$\dfrac{1336\times273}{300}\times\dfrac{700}{760}=1120~\mathrm{mL}$
 Suppose the equivalent weight of the metal is $\ce{E}$.
So, Equivalent Weight of metal Carbonate $=\ce{E}+30$
Because, Eq. wt. of ${\ce{CO3}}^{2-}=\frac{60}{2}=30$
Now,
 $$\begin{align}\text{equivalents of metal carbonate} &= \text{equivalents of }\ce{CO2}\\\frac{4.215}{E+30}&=\frac{1120\text{(vol. at NTP)}}{11200\text{(vol. of 1 eq. at NTP)}}\\\text{So, } \text{E}&=12.15~\mathrm{g/equivalent}\end{align}$$


texts: How to determine the amount of barium in a sample of contaminated water?

texts:
Here is the assignment I have:

  You are working for Matrix Pro - a company involved in analytical assessment and method development for the clean-up of contaminated waters.

  You received water samples from a potential client. The samples may contain the following ions: $\ce{H+, Ba^2+, OH^─}$

  The potential client requested a qualitative analysis of the sample as well as the development of a treatment technique that will bring the pH value to neutral and eliminate the barium ions. For comparison another water sample (considered to be non-contaminated) was also sent for similar qualitative analysis.

  Assignment

  Develop an experimental procedure to comply with the request of the potential   client.
  Draw a flow chart.
  Tabulate all your observations and data.

What I'm not sure about is finding the amount of barium present in the unknown sample so I can determine the amount of precipitating reagent to add.  I just want to know what type of analysis to do.  Chromatography? Spectrophotometry? Something else?


texts: How does dry air get saturated in the Ostwald-Walker Method?

texts:
This question was already asked and this was the answer that was posted:

"So basically, before you start the experiment the vapors have already formed, meaning that thermodynamic equilibrium has been achieved. Then you start bubbling through dry gas, which then mixes with the vapor gas already in the bubbles. If you set the gas flow appropriately, you get a near-equilibrium situation (see the graphic below) and the gas that exits the bulb assemply has exactly the same amount of vapor in it as the vapor "layer" (which can not be thought of as a layer anymore because of the bubbling) above the liquid surface.

We do not have an equilibrium situation, which is why so much care has to be taken that we get as close as possible to the equilibrium situation. (Also, we do not have a closed system, so everything starts to get slightly problematic at this point. But to a first degree of approximation, this will hold up fine.)"
(For more, visit: How does Ostwald-Walker method work? )

My questions are:

1) What is this 'near' equilibrium situation that is created?

2) If dry air gets saturated when it passes through the solution bulbs, then how is it able to absorb more solvent vapours when it is passed through the solvent bulbs?


texts: Why does a silane group react with hydroxyl groups?

texts:
I read somewhere that a silane group will react with hydroxyl groups.

Does anyone know why this would happen?


texts: When does ipso attack occur in electrophilic aromatic substitution?

texts:
My textbook doesn't mention the conditions required for an ipso attack to occur. It just describes some examples where groups like $\ce{-C(CH3)}$ and $\ce{-SO3H}$ are replaced by $\ce{Br}$ using reagents like $\ce{Br2}$/$\ce{AlCl3}$.
Can someone describe the required conditions in detail?


texts: Why is the +3 oxidation state of Cerium more stable than +4?

texts: For the 4f inner transition metals, +3 is the most common oxidation state (OS). Why is the +3 OS of cerium considered more stable than +4, at which it attains noble gas configuration?


texts: Where can I find the infrared band positions for phosphorus compounds?

texts:
I am trying to interpret an IR spectrum where I have $\ce{(NPCl2)3}$

I have $\ce{P-N}$, $\ce{P=N}$ and $\ce{P-Cl}$ bonds and it is cyclic.

Where can I find or does anyone know what the general ranges for these stretches are?

I found a website that told me $\ce{P=N}$ is around $1170 \, \mathrm{cm}^{-1}$.


texts: Treatment of allylic alcohol with thionyl chloride: why is the product rearranged?

texts:
I have read that $\mathrm{S_Ni}$ reactions involving the attack of $\ce{SOCl2}$ on alcohols proceed without the formation of discrete carbocations, and hence there is no rearrangement involved. But that doesn't explain this reaction:

Here, is the allylic carbocation formed, or is there a different explanation for this reaction?


texts: Why is sublimation considered a zero-order process?

texts:
In my Chemistry book, it states that sublimation is normally a zero-order reaction or process, as the concentration of molecules that have sufficient energy to sublime is limited by the solid's surface area. My book states that the concentration of these molecules does not change when the amount of subliming substance decreases.

However, I am struggling to understand one thing: if the amount of subliming substance decreases and the object gets smaller, wouldn't that have an effect on the surface area of the solid as well as a consequent effect on the rate of reaction?

Why exactly is sublimation zero-order when clearly the surface area of a solid is variable in different instances? According to me the only way for sublimation to be zero-order is if the solid is held in a sealed container and is under dynamic equilibrium with its vapor pressure. Am I correct about this? I would appreciate it greatly if someone could help me out about all this.


texts: Polar compounds that doesn't dissolve in water?

texts:
I'm studying for my exam introduction to chemistry. In the course, there's an exercise where we have to explain why something dissolves in water and why other compounds doesn't.

For me, if the substance is polar, than it dissolves in water because H2O is polar to. (and non-polar dissolves in non-polar).

The first example is AluminumOxide. In the course, it's mentioned that this doesn't dissolve in water. They say that the forces are to high? But it's a polar compound? How do you know if a polar compound will dissolve?


texts: Reference for assignment of symmetry (term symbols) of electronic states

texts:
I am looking for a textbook and/or internet resource where I can find the reference for assignment of symmetry of electronic states systematically.

For example, $$ \ce{^1\Delta^{}_{g}}, \ce{^3\Sigma^{}_{g}}, \ce{^1\Sigma^{}_{g}} \hspace{1em} \text{for ground state} \hspace{1em} \ce{O_{2}}$$


texts: How many protons are required to satisfy hydroxyamine's (NH₂OH) lust for protons?

texts: I ask because I'm trying to write an equilibrium equation for this reaction and I'm wondering whether an extra 2 protons will be required after one is taken to attack the $\ce{OH}$ group and turn it into $\ce{H_2O}$ in order to convert the freed ammonia (with one proton missing) into a conjugate acid.


texts: Order of reactivity of carbonyl compounds to Nucleophilic addition reaction

texts:
One of the questions in my textbook was to arrange the following in order of their reactivity for nucleophilic addition reaction.

$\ce{(p-NO2Ph)_2CO}$
$\ce{(CH3)_2CO}$
$\ce{(p-NO2Ph)COH}$
$\ce{CH3COH}$

I know there are two factors in play here. One is the steric factor (4>3>2>1) and annother is the electropositive nature of the carbonyl carbon, which is the site of nucleophilic attack (1>3>4>2). I am unable to decide which of these factors shall overpower the other and what shall be the final order?


texts: Why CO2 has 4 vibrational degrees of freedom?

texts:
If I have a diatomic molecule, so a linear molecule, $3N-5=6-5=1$ holds, since this vibrational degree of freedom corresponds to the stretching coordinate beetwen the two nuclei.

If I consider water for example, I have a nonlinear triatomic molecule, so the formula says $3N-6=9-6=3$ vibrational degrees of freedom. Also in this case it makes sense since they correspond to the bending angle and to the $2$ stretching lenghts.

While, If I consider $\ce{CO2}$, in this case I have a triatomic linear molecule, so $3N-5=9-5=4$ vibrational degrees of freedom. Of course $2$ of these correspond to the two stretching lenghts, but I really don't understand what the other two correspond to. Since the molecule is linear, there shouldn't be angle to consider, otherwise it would not be linear anymore.


texts: In many places, I read that Gibbs Free Energy is called "free energy" because some of the enthalpy that comes from the chemical reaction becomes "waste heat" due to a change in the entropy of the system, and only the rest is usable as work. However, I cannot imagine how this is the case. Take an exothermic reaction with a positive change in entropy for example. Because $\Delta G = \Delta H - T \Delta S$, then we find that $\Delta G$ is more negative than $\Delta H.$ That is, more energy is released by the system than the enthalpy of reaction. How does this fit in with the "waste heat" explanation, that not all of the energy released is usable? There is more energy released now.


texts:
A little while back, I introduced the feature to mhchem to properly format $K$ constant variables, like $\ce{Ka}$ rendering as $K_\mathrm{a}$, $\ce{pKb}$ rendering as $\mathrm{p}K_\mathrm{b}$, etc. (besides $\ce{K_a}$ and $\ce{pK_b}$).

I was inspired by seeing quite some usage of Ka, pKb inside \ce, here at Chemisty.SE. I also checked if there were other meanings of these terms and found none.

But now, I am getting doubts how future-proof this is. What if the next new chemical element's name will have the 'Ka' abbreviation? What if some field will invent the 'Ka' 'nickname'?

Do you know any other meaning of Ka, Kb, Kw, Kf, Kc, Kp, Ka1, Ka2, Ka3, Kb1, Kb2, Kb3, Keq, Ksp other than $K$ constants?
How likely is it that alternative meanings for these will emerge?

Or, to phrase it differently: How likely is it (or will it be) that somebody typing \ce{Ka}, \ce{Keq}, ... does intend other output than $K_\mathrm{a}$, $K_\mathrm{eq}$, ...?


texts: Why is helium a liquid at absolute zero? And why is it the only non-solid element at 0K? At 1 atm.


texts: Can a single monomer be a macromolecule? If so, when?

texts:
In our science class, we're learning about the four fundamental macromolecules in every living organism: carbohydrates, proteins, lipids, and nucleic acids. Our class definition of a macromolecule essential is:

  A macromolecule is a large molecule that is essential to all life, and present in all living cells. It is a polymer- a chain of monomers.

Our definition of a monomer is like so:

  A monomer is the simplest building block of a macromolecule with the properties of that macromolecule. They can be strung together to produce a macromolecule (usually by dehydration synthesis).

I would have no problem with these definitions if not for my teacher mentioning once that some monomers can also be macromolecules by themselves. Because some monomers of certain macromolecules- such as the monosaccharide glucose vs. the disaccharide sucrose or the polysaccharide amylose - can act on their own as an essential and functional carbohydrate, they are macromolecules by themselves.

Is this true? For example, could glucose be a macromolecule by itself?

Thanks.


texts: Which elements tend to form the most phases?

texts:
Some combinations of two elements have very complicated binary phase diagrams across the weight% horizontal axis. Others are rather simple. Is this a function of only one or both of the elements involved? I would think both. However, surely there are some elements that tend to form more phases than others. Has this tendency to form more phases (or less) been quantified for the various elements? If no, is it quantifiable?

Obviously elements form only a given number of known allotropes. However, it is not known if the number of known allotropes is exhaustive. Therefore the number of pseudomorphs in a binary phase diagram seems like a more thorough method of investigating an element's "binding flexibility."


texts: Special electron configurations in p block on periodic table?

texts:
Gold and Chromium have weird electron configurations, because electrons are differently divided : eg an electron jumps from a s-orbital to a d-orbital to have a half-filled s orbital and a fully/half filled d-orbital, which is much more stable.
But does this also occur with the p-orbitals? eg why does Fluorine not transfer an electron from its s orbital to its p orbital to have a  half-filled s orbital and a fully filled p-orbital, that would be more stable?


texts: Differences in Gibbs activation energies for rotation around a bond

texts:
Question
Why is there a difference in energy in the rotational barrier between these two structures?

My reasoning is such:

Due to conjugation between the O electrons and the pi- double bonds, the bond has actually single bond characteristics and is therefore weaker than a conventional double bond alkene. But that doesnt explain the difference between the molecules? Can someone please explain?


texts: What do 1T and 2H mean in front of compounds?

texts: I have seen 1T and 2H used as prefixes for metallic compounds in literature, but I am having trouble finding what they mean. For example, 1T-HfS2 or 2H-HfS2.


texts: Which is more stable? A phenyl carbanion or a disubstituted vinylic carbanion?

texts:
I came across a question which asks to work out the stability order for the following species-

b.
c. $\ce{R2C=CH-}$

Can the lone pair on phenyl carbanion participate in resonance?  If yes, then how? Also, how is that more stable than the vinylic carbanion?


texts: How to identify if a chemical equation has a 'fractional order'?

texts:
Consider the following reaction:
$$\ce{CHCl3 + Cl2 -> CCl4 + HCl}$$
The rate law expression is:
$$\text{Rate} = [\ce{CHCl3}]\cdot[\ce{Cl2}]^\frac{1}{2}$$
with an order of $1.5$. But 'how can we determine' this fact?
And why is it $1.5$ and not $2$?


texts: Spin interaction term for a two-particle system of fermions with a potential that contains spin-spin interaction

texts:
Consider a two-particle system consisting of two identical fermions in a potential $$V(\vec{r})\vec{\sigma_{1}}\cdot\vec{\sigma_{2}}$$ where $V(\vec{r})$ is the spatial part of the potential and the indices $1$ and $2$ correspond to each particle respectively and $\vec{\sigma}=\sigma_1i+\sigma_2j+\sigma_3k$ with $\sigma_{i}$ the $i$-th Pauli matrix.

I want to find the contribution of the spin interaction term to the energy of the system. Now, working with singlet and triplet states, I know that the energy will be analogous to the eigenvalue of each state respectively.
Working things out, I have found that the eigenvalue of the singlet state for $\vec{\sigma_{1}}\cdot\vec{\sigma_{2}}$ is $-3$ times the eigenvalue of the triplet state.
By also trying out as $V(\vec{r})$ a potential used in physics(Yukawa potential), I also found that the triplet state has the same energy as the case in which we have two bosons in that potential.

So, denoting the ground state energy of that potential for two identical bosons as $E$, the triplet state gives $E_{triplet}=E$ and the singlet state gives $E_{singlet}=-3E$.

So, the question is:
What is the physical explanation of this?.
And, why is the spin-spin interaction more "intense" for the singlet state than for the triplet state(by taking the absolute value of each state's eigenvalue)?

EDIT: Since I don't consider spin-orbit interaction, I think that the answer might have to do with spin-spin coupling because of the dependence on $\vec{\sigma_{1}}\cdot\vec{\sigma_{2}}$.


texts:
We know that ammonia undergoes amine inversion. Why doesn't the dipole moment decrease in ammonia, since the direction of the dipole changes to the opposite direction every time there's inversion?

Shouldn't the effective dipole moment become zero?


texts: Effect of magnetization on oxidation (rusting) of iron

texts:
Can magenetizing a piece of iron bar slow-down (or speed-up) the oxidation (rusting) process? In other words have any influence on it ?
From what I've looked up( wikipedia, quora), it appears that the property of magnetism depends on 'spin' and also the creation of bonds does have an impact on the 'spin' (apparently has something to do with pauli's exclusion principle).
PS: Tried to ask the question on physics.stackexchange.com but did not find all the tags so decided to ask here.


texts: How well (or poorly) does natural leather insulate?

texts:
What is the general thermal conductivity of animal skin leather?

I understand there are many different animal's skins (cow, sheep, buffalo, deer, pig), but in general, does natural leather insulate well (compared to, for scale, an esky for food insulation), or not?


texts: How do I neutralize copper sulfate blue tint on a sofa?

texts:
I accidentally poured some copper sulfate solution on my sofa.
So there is a blue halo on it.

Is there something I can put on it to neutralize that blue tint?

I was thinking of bleach, but 1- I don't know if it will actually do anything, and 2- It will surely damage the black dye.


texts: Do 2-aminoalkanes undergo iodoform test?

texts:
I was doing problems in an excercise book and they gave a list of compounds that may undergo iodoform test- which included 2-aminoalkanes.
I dont find any keto methyl gps or methyl carbinol gps that would give iodoform test that normally would give the test. Can someone shed some light here?


texts: Expression for the entropy of an ideal gas

texts:
I want to obtain the Sackur-Tetrode expression for the entropy of an ideal gas based on:

$$S = K_B ln \Omega$$

We have an isolated system with a fixed volume V and fixed number of particles
N and there is no energy exchange with the external world (what statistical mechanics calls micro-canonical ensemble).

We know that $\Omega$ is:

$$\Omega(N,V,E)=\frac 1 {N! h^{3N}} \int_{\mathcal H<E} d^N\mathbf p \ d^N \mathbf q \tag{1}\label{1} = \frac{V^N}{N!h^{3N}} \frac{(2mE \pi)^{3N/2}}{(3N/2)!}$$

When I plugged equation 1 into  $S = K_B ln \Omega$ I got:

$$S = K_B ln \Omega = Nk_B ln [\frac{V}{N}(\frac{4mE \pi}{3 h^2 N})^{3/2}]$$

Which is incorrect as I should have gotten:

$$S = K_B ln \Omega = Nk_B ln [\frac{V}{N}(\frac{4mE \pi}{3 h^2 N})^{3/2}] + \frac{5}{2}NK_B$$

Why I am not getting the term $\frac{5}{2}NK_B$?


texts: Why is the reported melting point of formaldehyde so different from the triple point?

texts:
All of the (believable) sources at PubChem and most of the sources at NIST give 181 K for the melting point.
The one source I can find for the triple point is NIST, which gives 155 K.
There are two possibilities I can think of, but I can't confirm or deny either:

The triple point value is wrong.
The density of the solid is very different from the density of the liquid, as suggested by the Clapeyron equation.

The densities of two of the solid forms, oxidane and paraformaldehyde, are quite different from the liquid density, but it doesn't look to me like they form spontaneously by simple cooling. Maybe I'm wrong about this.
What is the true reason for the difference?
Edit: To clarify, I understand that the triple point has two values, one of pressure and one of temperature. I'm not so interested in talking about the pressure of the triple point of formaldehyde unless it helps answer my question, and that's why I didn't mention it at first.
I think my question is interesting because in the data I've seen so far, the difference between the temperature value of formaldehyde's triple point, and the temperature of its melting point, is much greater than that of any other compound.
Maybe I've been extremely unlucky and formaldehyde's difference actually isn't unusual, and the compounds I've reviewed are the unusual ones. This would also be interesting to learn.


texts: IUPAC name of a molecule with a cyanide group and a double bond

texts:
This is the molecule:

After identifying the functional group, what should we prefer? A longer carbon chain or the one which is short but has a double bond in it.

I personally think that we should go for longest carbon chain. So the name should be 2-ethenylpentanenitrile.


texts: What other intermoelcular forces can exist between neutral molecules?

texts:
What kind of intermolecular forces can exist between neutral molecules?

My answer was London dispersion.

My logic was this: London dispersion is the only thing weaker than dipole-dipole, and as far as I am concerned two neutral molecules can't be attraced by dipole-dipole forces because you need a positive end on one and a negative one on the other: but there cannot be because, well, both are neutral, no?

  What are the intermolecular forces present in $\ce{CH3CH2NH2}$?

My answer was also London dispersion because it appears like this molecule is neutral.

Both answers are wrong. It appears I don't properly understand intermolecular forces. Why are my answers wrong?


texts: How do I arrive at the mass of solvent from a molar fraction concentration?

texts:
So the question says:

  If the mole fraction for $\ce{H2SO4}$ in an aqueous solution is $0.325$, what is the mass of water (in grams) in $100\ \mathrm{mL}$ of solution?

Me, and my other classmates tried to solve this one but we didn't reach a fully correct answer and our teacher arrives at a different answer.

My answer is:

Since X(H2SO4) + X(H2O) = 1

So: 1-0.325=0.675

X(H2O)=0.675

The mole percent is (0.675*100)=67.5%

1 mole percent = 0.01 mol

H2O moles = 0.675mol

H2O mass (g) = (0.675) * (18) = 12.15 g

Teacher is not convinced with this answer and say its wrong because the total must be 100g, and if the H2O mass is 12.15g then H2SO4 mass will be 31.85g, and 12.25+31.85 dont equal 100.

His answer is simple as follows:

1-0.325=0.675

0.675=67.5% of H2O

H2O mass= 67.5g


texts: Loss of aromaticity vs low entropy of activation

texts:
Even if reaction has low entropy of formation does that mean it is favorable to loss aromaticity and form highly strained cyclopropane ring? Why this reaction happens? Maybe someone can explain that in more details? Is this equilibrium reaction? I assume cyclopropane ring can be as easily opened with nucleophile as it closed? It does not make any sense for me here. Thank you for comments.
This is quoted from "The Art of Writing Reasonable Organic Reaction Mechanisms", Second Edition by Robert B. Grossman, DOI: 10.1007/b97257.

The reaction proceeds by an $\mathrm{S_N2}$ mechanism. The reaction has a very low entropy of activation, so it proceeds despite the loss of aromaticity. The product is a model of the antitumor agent duocarmycin. DNA reacts with duocarmycin by attacking the $\ce{CH2}$ group of the cyclopropane ring in an $\mathrm{S_N2}$ reaction.


texts: Why do alpha-hydroxy ketones respond positively to Tollens', Fehling's, Benedict's, Schiff's and HgCl2 tests?

texts:
I learnt from a certain textbook that aldehydes and formic acid respond positively to Tollens', Fehling's, Benedict's, Schiff's and HgCl2 tests.

However, in another textbook I read that even alpha-hydroxy ketones respond positively to these tests. What is the reason behind this? I thought ketones are not oxidizable (unless under drastic conditions).

Fructose is an alpha-hydroxy ketone, but all alpha-hydroxy ketones are not fructose. In fructose there is a terminal hydroxy group which facilitates Tollens' test, etc. in basic medium. But why do alpha-hydroxy ketones like benzoin give these tests even though there is no terminal hydroxy group? That part is still unclear to me. Could you please answer that part?


texts: I need a good resource that explains the concept of chemical equivalence and its various application in physical chemistry. I have not found anything worthwhile from a Google search.


texts: Effect of specific heat capacity on heat loss

texts:
Assume we want to calculate the heat capacities of two substances with different heat capacity. We heat them both up with a immersion heater delivering a constant rate of energy (constant J/sec), and we stop the immersion heater after 100 J of heat has been added. Would the lower heat capacity substance experience more or less heat loss, and would that translate into more or less error in the calculated specific heat?
I assume that less heat loss would mean less error but I am not sure as to which substance would experience less heat loss.

If anyone stumbles across this later, I am now strongly learning towards more heat loss for lower heat capacity because heat loss is proportional to temperature difference and lower heat capacity will change temperature more easily.


texts:
This is a question from the Cambridge International Examinations October/November 2017 (pdf from papers.gceguide.com, pdf via the Wayback Machine).

I need to understand why the secondary amine in the serotonin molecule does not undergo condensation reaction with $\ce{CH3COCl}$.
Because, as far as I know, there should be an amide formation for this reaction.

Here's a picture of serotonin:

I must be lacking some information making that $\ce{NH}$ unsuitable for this reaction. And I know that the other amine and the phenol reacts with $\ce{CH3COCl}$.


texts: How can I purify Ferric or Ferrous acetate with a very basic lab?

texts:
I’ve been trying to make Ferric acetate by mixing vinegar with steel wool and allowing it to react. The result is successful in dying leather or wood black and acting as a mordant. Theoretically there are ways of crystallizing, precipitating, filtering, or separating it with solvents.

There is only one problem: I can’t remove it from the vinegar solution without it oxidizing. Adding Hydrogen peroxide causes it to create iron oxide, heating it causes it to hydrolyze and create iron oxide. Leaving it in solution turns some of it into iron oxide.

One idea I had was using glacial acetic acid instead of vinegar but I’m hoping I don’t have to because that’s fairly expensive. I could also do the entire thing under vacuum but it still wouldn’t fix the hydrolysis reaction. Could I maybe crystallize it? I’m open to suggestions with an emphasis on stuff that doesn’t require expensive reagents or obscenely overpriced labware.


texts: Lifetime measurement: double peak in instrument response function

texts:
I am measuring flourescence lifetimes with a picosecond pulse laser, using the LifeSpec II with an MCP detector. Instead of a single peak rapidly decaying, as would be expected, my IRF contains two peaks. I am suspecting some sort of reflection causing this. Does anyone get what I mean here? Could add a graph soon if that might help.

EDIT: I have realized this might not be an error, but I would still like to know why.


texts: How are electronic configurations determined experimentally?

texts:
Despite the ubiquitous usefulness of electronic configurations (of elements) in explaining their behavious I have not been able to find out exactly how the configurations are determined.

Is there any sure-fire technique to detect them (like x-ray diffraction for crystal structure) or is it based on guesswork, through observation of the various properties and reactions of the elements?


texts: Mass of sugar that was added to the water (Raoult's law)

texts:
Water has a vapour pressure of $15.5~\mathrm{mmHg}$ at $25~\mathrm{^\circ C}$. An unknown amount of the non-volatile sugar glucose ($\ce{C6H12O6}$) is added to $1.31~\mathrm{kg}$ of water and the vapour pressure of the system is found to decrease by $0.13~\mathrm{mmHg}$.  What mass of sugar, in grams, was added to the water?

I'm a little bit confused about this problem.

Here it says that after the sugar was added to water, vapour pressure of the system is found to decrease by $0.13~\mathrm{mmHg}$.

Does it mean that before sugar was added, there was only one element $\ce{H2O}$?

And I used Raoult's law:

$$P_i = x_iP_i^*$$

where $P_i$ is the vapour pressure of the solvent, $x_i$ is the mole fraction of the solvent, and $P_i^*$ is the vapour pressure of the pure solvent.

So can I use this to find the partial pressure before the sugar was added?

I know that $1.31~\mathrm{kg}$ of water is $72.78~\mathrm{mol}$.

And if my assumption is right and before sugar was added there was only water, will the mole fraction before sugar was added just be $72.78$ since there was only $\ce{H2O}$?


texts: Why can NCl3 be hydrolyzed but CCl4 cannot?

texts:
While explaining why $\ce{CCl4}$ cannot be hydrolyzed, we say carbon atom doesn't have any d-orbitals and therefore a water molecule (lone pair electrons of $\ce{O}$ atom) cannot form coordinate bond with carbon. So, $\ce{CCl4}$ cannot be hydrolyzed.
In $\ce{NCl3}$, nitrogen also does not have any d-orbital.

Why it can be hydrolyzed?

Is hydrolysis mechanism for $\ce{CCl4}$ and $\ce{NCl3}$ different? If so how they are different?

Again, in some sources I have found, in the case of $\ce{NCl3}$ water forms coordinate bonds with the $\ce{Cl}$ atom and hence the molecule gets hydrolyzed. Why does the same thing thing not happen in $\ce{CCl4}$ which also has a $\ce{Cl}$ atom?


texts: How exactly is energy created by oxidative phosphorylation

texts:
I understand how the protons and electrons move around through various carriers, shuttles and proteins, but there's this talk of electrons being in "lower in energy" at the end. What does that mean? How is an electron lower in energy?

Also why do they need an electron acceptor? What would happen if there was no $\ce{O2}$ to accept the electrons? Wouldn't they just bind to something else?


texts: Even though nitrogen is less electronegative than chlorine according to Pauling scale bit why don't it form hydrogen bonding as effective as of nitrogen ? ( Electronegativity valve of  N =3.0,Cl=3.2)


texts: What's the difference between atomic orbitals and energy levels?

texts: If I'm drawing a Bohr model of Neon, the middle is the nucleus, the first energy level contains 2  electrons. The second level contains 8 electrons. 8+2= 10, Neon's atomic number. But then what are the atomic orbitals, like s, p, d, and f. Where do they come in? Are they completely different from the energy level?


texts:
I am experimenting at home with the idea of making an optical pH sensor that can read the colour of pH indicator using photodiodes.
I am wondering if there is some kind of ion permeable membrane that could be used to contain the indicator solution, so it can 'read' the pH of the solution being tested, without mixing with it.
I would like something that is fairly easily obtainable to me as a home experimenter.
The sensor could possibly be used make an automated pH corrector for my local aquaponics farm.
I looked into commercially available pH sensors. The glass bulb type and ISFET type suffer from drift and need regular calibration. There are optical types available, but they are too expensive for me.


texts: Harnessing phase separation to easily make Li film

texts:
I want to make a thin, smooth film of pure lithium in a glovebox.

In general, I think that I can use a phase separation approach. I will heat a bath of mineral oil above Li's melting point, then pour liquid Li inside and let it cool slowly. The Li should cool on top and the only curvature should be due to miniscus effect.

I would think that if I used a third, lighter liquid than the Li, I could put a large column of it on top of the Li. However, this requires having a lighter liquid. Li, at melting point, has a density around $\pu{500 kg m-3}$.

Can anyone suggest a suitable lighter liquid?


texts: Why is the CASSCF method multi-configurational, while the CI method is not?

texts:
The CASSCF method is perhaps the most commonly used theoretical method for studying difficult chemical systems exhibiting multi-reference character or non-dynamical/static/strong correlation. CASSCF is quite similar to CI, in the sense that a full CI wavefunction is generated within the active space used in the CASSCF method.

However, the CI method is a so-called ground state method, while the CASSCF method is multi-configurational. My question is simply "Why?". I feel it may be related to that during the CASSCF optimization, both the orbitals and CSF expansion coefficients are optimized, while in CI only the expansion coefficients are optimized. But I fail to understand how optimizing the orbitals gives the CASSCF method its multi-configurational nature.


texts:
Question:

Attempt:
The first reaction is addition of hydrogen halide. The reaction follows markovnikov's rule. The two possible products of the first reaction are:

For each product, the carbocations formed are:

After the formation of carbocation, $\ce{Cl-}$ attacks the carbocation forming a dihalide.
The final product after second reaction depends on the above intermediates.
The second carbocation faces electron withdrawing inductive effect and electron donating resonance effect from chlorine. But for halogens, inductive effect is more than resonance effect. So the carbocation is destabilized. So I chose option (A) as the answer since the first carbocation is formed.
But the answer given is (C) which means the second carbocation is formed.


texts: My textbook says 2-bromobutane is chiral, but it look like it will form superimposition mirror image


texts:
I can think of 4 products I have with rubberized plastic surfaces on them that have degraded over time. (IKEA scissors and kitchen knife, Logitech wireless mouse, Rocketfish wireless keyboard.)

The rubberized surface has become gooey and sticky after years of (minimal) use, to the point where it leaves visible residue on my skin or I leave fingerprints in it.  The back of the keyboard became sticky like glue.

At first I thought it was just one product and the factory screwed up the plasticizer mix, etc.  But now that it's happened in multiple products from multiple companies, is there something in my environment that could be making this happen?  Humidity?  Sunlight?  (I don't think the mouse or keyboard were in the sun much.)  A chemical in the air?


texts: Could we possibly discover new extraterrestrial elements and minerals?

texts:
So, after dissolving a good portion of my brain by watching a ton of sci-fi, I started thinking about all of the strange new materials that we will supposedly have in the future. For example, the ever-present "di-lithium" in Star Trek. But, as I started thinking about it, I thought it was a little ridiculous (I know science-FICTION) that all these exotic elements could exist. No matter where a species comes from in the galaxy or universe, they would be working with the exact same Table of Elements as us. Furthermore, so long as they are similar to human-life, i.e. they breathe oxygen, need water, etc., and therefore live on similar planets, wouldn't the compounds be the same as well?

Let's say we are 250 million years into the future and have discovered superluminal space-flight at 100,000,000c. Say we cruise around to inhabitable planets throughout the galaxy and universe. Upon landing on these new worlds, the elements and compounds we find would be the same that occur on Earth, right? Would we still find diamonds, rubies, uranium, iron, etc.? Or is it possible that there are combinations of the elements yet unknown? Is it for certain that we have catalogued every element and isotope that occurs naturally? I understand that new compounds could be formed, but as far as the base elements and the naturally occurring minerals, have we found them all?


texts: Could an ester react with magnesium oxide?

texts: Esters undergo saponification in the presence of hydroxides. Assuming anhydrous conditions, would they react with magnesium oxide?


texts: Hybridization and bonding in ethenone H2C=C=O?

texts: My book says ethenone is a planar molecule, so I was trying to understand its hybridization,I feel that like allenes ethenone too will not be planar. Supposing oxygen and the carbon near it to be in the xz plane and assuming that the pi bond between them involves py orbital of carbon, this implies the bond between that carbon and the adjacent carbon involves the pz orbital of that carbon. This implies that the end carbon's hydrogens will be in xy plane. What is wrong with my understanding?


texts: Finding wavelength of the centre of Stokes Ro-vibrational spectrum

texts:
I have the following rovibrational Raman spectrum for $N_2$:

and I am trying to calculate the "wavelength where the centre of the Stokes ro-vibrational spectrum would be observed" if the $N_2$ is excited with a 532nm Nd:YAG laser. I am very unsure of how to do this. I think I need to use the fact that Stokes transitions are given by $\tilde v = \tilde v_0 - 4BJ-6B$ ($B=$ rotational constant, $J=$ rotational quantum number and $\tilde v_0=$ excitation wavenumber) and that the separation between Stokes and Anti-Stokes lines is approx. $4B$. I don't really know how to make use of this information though nor what exactly is meant by the "centre" of the Stokes ro-vibrational spectrum. I'd appreciate it if someone could help me work through this.


texts: How to Predict the Formation of Racemic Mixtures or Single Products from a Diels Alder Reaction?

texts:
So far, I understand the mechanism of the Diels Alder reaction and am able to correctly predict the product of some slightly complex examples.

However, it seems that in some examples, a racemic mixture is formed, whereas in others that's not the case.

I have basic understanding of the Endo Rule (endo product favored over exo product), but have trouble with the stereo chemistry involved.

I also know that the symmetry of the diene and dienophile has to do with it, but can't seem to find a consistent pattern.

Any help would be appreciated.


texts: Are a meso compound and its mirror image isomers?

texts:
How are meso isomers even isomers? By definition, meso isomers are compounds that are superposable on their mirror images, but doesn't that mean that the mirror image is just the same compound?

Can someone explain the concept of meso isomers and diastereomers to me?


texts: Calculating the strength of an ionic bond that contains poly-atomic ions

texts: So the bond association enthalpy for ionic compounds like $\ce{NaCl}$ and $\ce{NaBr}$ can be easily calculated from a Born-Haber cycle. But the way a Born-Haber cycle is constructed it uses info that only really applies to mono-atomic ions like $\ce{Cl^-}$. So how would one calculate the strength of an ionic bond for ionic salts that contain poly-atomic ions like $\ce{NaOH}$ and $\ce{K_2SO_4}$. Is there a completely different method, or can a Born-Haber cycle be adapted to use a poly-atomic ion?


texts: Aromatisation of a ring which includes nitrogen

texts:
Question

Complete the following reaction sequence:

Answer

My solution
I was able to complete all the steps except for the last one. This is what I ended up with:

What I'm not getting is how the $\ce{-OH}$ groups are removed and the ring is aromatised. If anyone could provide me with a mechanism for the same, it would be really helpful.


texts: How to minimize surface adsorption by choice of material?

texts:
I need to do buoyancy experiments in vapours consisting of organic molecules in air using a microbalance. This involves measuring the change in weight of a sealed glass sphere when exposed to the gas. The problem is that surface adsorption shows up as significant noise. Is glass the best material for this? What properties determines adsorption, and how can I minimize it?

I assume it is a function of surface energy. For example PVDF has an energy about 10x less than glass. However, does this simply mean that it is easier to get rid of the adsorbed molecules rather than limiting the quantity in the first place?


texts: Is Using HSAB to Explain Michael Donors and Michael Acceptors Valid?

texts:
Basically, I've recently been thinking about using HSAB theory to rationalize the concept of michael donors and michael acceptors. Essentially, if we have a deprotonated diketone (with a lone pair on the alpha position carbon) or the Gilman reagent, it attacks the carbon in a vinylic ketone in a 1,4 addition.

However, if we used a Grignard reagent, than it attacks the carbonyl carbon in a 1,2 addition.

How can we use HSAB theory to justify this? I've figured out that the carbonyl carbon's LUMO is the pi-star orbital while the vinylic carbon center's LUMO is also the pi-star orbital except with the carbon bonded to another carbon, thus it should be higher in energy than a pi star orbital bonded with an oxygen.

I've also figured that the carbon nucleophile center on a Michael donor (such as that of the diketone) should be "softer" than the nucleophile center on a Grignard reagent's carbanion because the charge is less concentrated due to resonance and thus the HOMO of the Michael donor is not as high as the HOMO of a Grignard reagent.

However, I do not know where to go from here. Can someone help me what I'm doing wrong?


texts:
Whenever I read about coordination compounds in my textbooks, I always find a discussion about spin-only magnetic moment which is given by $\sqrt{n(n+2)}\cdot\mu_\mathrm{B}$, where $n$ is the number of unpaired electrons and $\mu_\mathrm{B}$ the Bohr magneton.

I'd like to know how to calculate the total magnetic moment of a given atom (spin only + orbital). For example let's take $\ce{Ni^2+}$. The spin only magnetic moment comes out to be $\sqrt{8}$ BM. Now how do I add the orbital magnetic moment? I've seen a bunch of expressions for orbital magnetic moment in terms on quantum numbers $n$ and $l$, but I am unable to understand which one to add.


texts: Is beryllium difluoride covalent or ionic?

texts:
My textbook  says that despite the large electronegativity difference $\ce{BeF2}$ is covalent since the beryllium ion will have too much charge density and it will attract the fluorine electron cloud and therefore forms polar covalent bonds.

I looked it up on Wikipedia and found out that it has a crystal lattice,  is soluble in water, and has a quite high melting point.

What else does one need to call a compound ionic? Am I or the textbook right?


texts: Which chemical reactions occur between my tongue and the food I eat?

texts:
There are various chemical reactions that can occur between materials.

Which chemical reactions occur with the tongue?
How come all reactions are reversible (nothing sticks to my tongue)?
What's special about the tongue-water interaction that makes it tasteless?


texts: Can reversible reactions proceed by different mechanisms in the forward and reverse directions?

texts:
It seems odd to me that this would be the case, but it also seems odd that it wouldn't.
Imagine a mechanism for a (forward) reaction that includes a slow reversible step and a fast irreversible step:

$$
\begin{align}
\ce{A &<=> B} &\quad &\text{(slow)} \\
\ce{B &-> C} &\quad &\text{(fast)}
\end{align}
$$

If the second step is irreversible, it's presumably going to be highly unfavorable to run in the reverse direction, and so there ought to be some alternate mechanism with a lower $E_\mathrm{a}.$ Is it possible that the reverse reaction is more favorable by a different mechanism? If not, why not?


texts: I recall being told that for a given reaction, every 10 degree rise in temperature the reaction rate approximately doubles. Is this true?


texts: Number of stereoisomers of 1-(2-methylcyclohexyl)ethan-1-ol

texts: How many stereoisomers are possible for the compound in the picture? I tried to draw a rough picture and indicated the chiral carbons. I'm getting 8 stereoisomers are possible but my book gives the answer as 2. Can someone explain where I'm going wrong?


texts: Clarifications about the mechanism of the Wittig reaction

texts:
Ok so this is the proposed mechanism for the Wittig Reaction as stated by my textbook, LG Wade. I have some doubts regarding this mechanism:

  1) Why is only triphenyl phosphine used here? Why not some stronger
  nucleophile like say trimethyl phosphine?

  2) Why would the lone pair on P attack the C of the alkyl halide in the
  first place? Isn't the lone pair in resonance with the benzene ring?

  3) Why is butyllithium used particularly.Can't any other reagent be
  used to abstract H ?

  4) Why is the four membered ring formed in step 2?

  5) Why does the ring collapse in step 3?

Note: I'm just a beginner in organic chemistry (Org 2) so it would be helpful if you can keep adjust your answer to suit my level of understanding.


texts: Why do galvanic cells need a salt bridge while electrolytic cells don't?

texts:
I see the questions of why a galvanic cell needs a salt bridge and why a electrolytic cell doesn't need a salt bridge being answered separately but I still can't grasp why you are not allowed to mix or interchange the reasons of the two. Can someone explain why both cells are set up in that way and provide a comparison?
From what I've read, it has to do with some of the following differences but I can't seem to put it together into a common picture.

A galvanic cell needs to prevent electrolyte mixing in order to produce current. Of course electrolytes need to be connected in order to maintain neutrality. But instead of a direct connection such as using the same electrolyte for both electrodes, the electrolytes for the anode and cathode are separated but connected by a salt bridge in order to maintain this neutrality but prevent the electrolyte mixing by having ions pass at a rate not too high. Could someone explain again what electrolyte mixing has to do with the current? Meanwhile since in an electrolytic cell, the chemical reactions are what is being produced the electrolytes can be mixed.
The electron supply in both are different. For a galvanic cell, it is supplied by the species getting oxidized. For an electrolytic cell, the external battery supplies the electrons.
I should also reiterate here how galvanic cells have spontaneous chemical reactions and do not need the external voltage supply while electrolytic cells have nonspontaneous chemical reactions and need the external voltage supply.
For a galvanic cell, the anode is negative while the cathode is positive. For an electrolytic cell, the anode is positive while the cathode is negative. However, it should be noted that by definition an anode always has oxidation while a cathode always has reduction.
It should be noted that the flow of electrons is the same when based on the charge of the electrode. Electrons always move from the negative electrode to the positive electrode. For galvanic cell it is anode to cathode while for an electrolytic cell it is cathode to anode.

It's not like I can't understand the two concepts of the galvanic and electrolytic cells separately. But I want to be able to fully understand the comparison and contrast on why you can't just interchange the two and how their many opposites and differences have something to do with that.


texts: What does the ZZE tag in an Chemical Table file refer to?

texts:
I have a number of Chemical Table files which include a "M  ZZE" tag in the properties block.

For example, in Galactobuxin, I have:
M  ZZE  1  31  23

In Rubrobrassicin there is:
M  ZZE  3  28  23  36  23  48  23

In R-hexanoyl CoA there is:
M  ZZE  1  55  23

The typical format for such tags is that it starts with an M, followed by two spaces. Then there is a three-letter code, in this case ZZE. Other codes include ISO (for isotope) or CHG (for charged atoms in the compound), then a number which indicates how many records on that line. This is followed by the actual data.
So
M  ZZE  3  28  23  36  23  48  23
would probably mean that there are three sets of ZZE data, being "28 23" "36 23" and "48 23". In every record I have the second number is 23.

The ZZE tags seem to occur only for compounds containing ribose rings, and the first number is the index of one of the bonds inside the ribose ring. Specifically, of three three bonds adjacent bonds with a stereochemistry marker, it always refers to the one in the middle:

I'm guessing the 23 is some property of the bond: so in rubrobrassicin the 28th, 36th and 48th bonds (there's one, and only one, ZZE record for each of the ribose rings in rubrobrassicin).

Does anyone know what the ZZE property in a chemical table file refers to, or what it indicates? I can't find any information on the format.


texts: Why is the Jacobsen's catalyst with tert-Butyl groups a better catalyst for epoxidation?

texts:
In an experiment I synthesised the below Jacobsen's catalst:

I used it to create styrene oxide through epoxidation. Chiral GC analysis showed that the enantiometric excess was lower compared to using Jacobsen's catalyst with tert-Butyl groups (shown below). This leads me to believe that it is more enantioselective, but why is this?


texts: What is the unit of the Rydberg Constant?

texts: In the image, the Rydberg constant seems to have two units. How is that possible?


texts: Will evaporation from two immiscible liquids blow up a balloon?

texts:
Consider the following setup:

Two immiscible liquids A and B are placed inside a balloon at a temperature where neither one of them boils. The inside of the balloon contains some argon, and the outside is air at atmospheric pressure. The balloon is made of mylar or some other similar material (flexible but not elastic).

I expect that the volume of the balloon would increase a bit due to evaporation of A and B into the argon. If we start without any gas in the balloon, is there a scenario (choice of liquids, choice of temperature) where the combined evaporation of A and B will be sufficient to fill up the balloon?

This question is related to Is it possible to boil a liquid by just mixing many immiscible liquids together? It addresses the question how to get both liquids into contact with the gas phase without worrying that the more dense liquid would be covered by the less dense one. It specifically does not ask about boiling, though, but rather about combined vapor pressure higher than ambient pressure, i.e. sufficiently high to displace gas at atmospheric pressure.

If this setup works, I wonder if it is possible to build a balloon pump where the balloon blows up "automatically", i.e. by heat transfer from the environment to drive evaporation of the two liquids.


texts: Organic Chemistry - Effect of methyl substituent in Aromatic Substitution via Benzyne

texts:
The following reaction has been taken from my study material. This shows that the benzene ring is undergoing a nucleophilic aromatic substitution via benzyne mechanism (presence of a strong base like $\ce{NaNH2}$). My question is:

Why is substitution preferred at the ortho position?

The following link explains the mechanism quite well and gives an example of ortho-chlorotoluene undergoing a similar reaction. Since both proceed via the same benzyne intermediate, why is there a difference in the products formed by meta-chlorotoluene? Or is my study material wrong in saying that o-aminotoluene is a major product? Any help regarding this is appreciated!

Attaching the related reaction's image:


texts: Composition of carbon rods in alkaline batteries

texts: The carbon rods in batteries look somewhat similar to graphite, but they do not leave a significant mark on paper. What form of carbon are they? Are they simply just graphite with a large amount of binder (clay) mixed in?


texts: Help with mechanism similar to Robinson Annulation

texts:
I need to figure out a mechanism for this reaction. All I know is that it is supposed to have a similar mechanism to Robinson Annulation.
This is the best I could come up with, but I've been told it is incorrect.

When trying to correct this, the only thing I could think of is that maybe in the cis configuration the ethoxy group provided too much steric hindrance for the second bond to be formed. In that case, I could have

I am far from sure about this. Can you guys help point me in the right direction?
Edit:
Apparently the correct mechanism is

As far as I can tell, I was marked off for not adding and then immediately abstracting a proton at the same position, and I was marked down for this twice. I thought the point of a mechanism was to show the most direct way to reach the product-why would I bother to add a proton to an intermediate, just to take it away the next step, leaving me with the same intermediate, and the same next step? Maybe someone here can explain why my omission is significant.


texts: The IUPAC name of sodium nitroprusside, and back-bonding in it

texts:
In the standard test for the sulfide ion, sodium nitroprusside $(\ce{Na^_2[Fe(CN)5(NO)]})$ is used. The IUPAC name for this compound as stated by Wikipedia is sodium pentacyanidonitrosylferrate(II)

I have three queries related to this:

Does the nitrosyl ligand donate a pair of electrons (through back bonding) to form $\ce{(NO)^+}$ or is $\ce{(NO)^+}$ the ligand?
In both the cases I guess the name should be sodium pentacyanidonitrosoniumferrate(II) instead.
Now the product formed after the sulfide test is $\ce{Na^_4[Fe(CN)5(NO)S]}$ whose IUPAC name is sodium pentacyanidonitrosylsulfidoferrate(III). But the nitrosyl ligand is neutral in this case. So why in this case there is no back bonding?


texts: Why do larger alkyl groups show a greater inductive (+I) effect?

texts: I have been taught that an alkyl group shows a +I (positive inductive) effect. Why do they do so? I know that hyperconjugation can explain how alkyl groups could stabilize a carbocation (better than a hydrogen). But, how does a longer chain alkyl group (or a bulkier alkyl group) show more +I effect than a smaller one?


texts: Why isn't this molecule named 2-fluorocyclopent-1-one?


texts: Can sensitive nuclei like 1H be exploited to obtain 13C spectra?

texts:
Measurement of 13C-NMR is essential for characterisation of compounds in organic synthesis, however, sensitivity can often be an issue, especially as molecules get larger and quantities get smaller, due to the low natural abundance of the NMR active 13C nuclei.

Standard carbon NMR is ran using a single pulsed experiment with heteronuclear decoupling for the 1H nuclei. This decoupling improves sensitivity by focusing the multiplets into a single sharp peak, with added sensitivity gained due to the nOe. Even with this enhancement, it can still often be difficult to obtain satisfactory spectra without resorting to using a stronger magnet (500 MHz/600 MHz is standard, the use of the 800 MHz spectrometer is prohibitively expensive for routine work) or running thousands of scans (there's a limit to how well this works anyway due to natural drift leading to peak broadening over time).

Unlike the standard 13C-NMR experiment, many 2D experiments such as HSQC are able to record data for 13C by observing the 1H nuclei (this is a huge oversimplification, I realise). This does, of course, lose the data for quaternary carbons, but I believe there are ways to get this data back (DEPTQ and various 2D experiments for example).

Why then are we unable to record 1D heteronuclear NMR using a similar technique?


texts:
My book says:

  $\ce{NaCl}$ shows metal excess defect, which results into the formation of an F-center in the crystal. This F-center is responsible for the yellow color of $\ce{NaCl}$.

How does an F-center provide color to the solid?