texts: Identifying the structure of an amino acid from NMR spectra

texts:
I have the 1H, 13C, and DEPT spectra of an unknown compound, listed in text form below, but I have also attached original images of the spectra. I know that it is an amino acid that has a cyclic structure and a relative molecular mass of 145. I'm supposed to deduce the structure, but am having some trouble with it:

1H NMR (in D2O): 4.2 ppm (1H, s), 3.85 ppm (1H, dd), 3.2 ppm (2H, m), 2.1 ppm (1H, d), 1.8 ppm (3H, m) (image of spectrum)

13C NMR: 174.27 ppm (quaternary), 61.92 ppm (CH2), 54.09 ppm (CH2), 38.69 ppm (CH/CH3), 32.87 ppm (CH/CH3), 28.04 ppm (CH/CH3) (image of 1D 13C spectrum; image of DEPT spectrum)

From the spectral data, I can tell that the compound doesn't have an aromatic ring, but beyond that I don't know how to proceed. Unfortunately, although it would be really helpful, I'm not able to determine the coupling constants in the 1H spectrum.


texts:
When studying about catalysts I normally come accross volcano plots like the one shown below:

What confuses me is how are the two lines fitted, how do you determine what points to include and what points not to include. For example I could have included the two points for Pt and Ir to obtain a slightly different shape of the volcano plot. Is there a guidline for this?


texts: Why is atomic orbital one electron wave function? Why distance from centre is proportional to angular wave function?

texts:
Consider the following statements:

  An atomic orbital is one electron wave function $\psi(r,\theta,\varphi)$ obtained from the solution to the Schrödinger equation.

There two electrons in an atomic orbital, so shouldn't atomic orbital be two electron wave function? Or since we get three eigenvalues from Schrödinger's equation, not four, so atomic orbital is one electron wave function?

  In angular wave function plots, the distance from the centre is proportional to numerical values of $\Theta\Phi$ in that direction and is not the distance from centre of the nucleus.

Distance is from which centre if not from centre of nucleus? Also why distance from centre is proportional to $\Theta\Phi$?

Lastly, I guess, it is impossible to plot the variation of $\psi$ with $r,\theta,\varphi$, because it would require 4 axis (or four-dimension graph). Am I right?


texts: What makes charcoal a good adsorbent to organic and non polar substances while alumina and silica are best for polar substances?

texts: My question is, what makes charcoal a good adsorbent to organic and non polar substances while alumina and silica are best for polar substances?


texts: How does di-isobutylaluminium hydride ( DiBAl-H ) reduces carboxylic acid

texts: $\text{DiBAl-H}$ reduces by electrophilic attack and provides hydrogen by $\text{H}^-$ transfer. Unlike $\text{LiAlH}_4$ it does not directly provide $\text{H}^-$ ion. So it should not undergo acid base reaction with carboxylic acid. But my friend argued that it undergoes acid base reaction. I can't find any reaction mechanism for reduction of carboxylic acid with $\text{DiBAl-H}$, can someone propose a mechanism for it?


texts: Friedel-Crafts alkylation of five-membered heterocycles

texts: The five-membered heterocycles pyrrole, furan, and thiophene undergo Friedel-Crafts acylation, but I have not seen them undergoing a simple Friedel-Crafts alkylation reaction with a Lewis acid such as aluminium chloride. Why is that so?


texts: Method to find out the amount of solvent replaced by another solvent

texts:
So I am performing a relatively simple coprecipitation experiment to synthesize ceramics. All my precursors are in aqueous solutions. But due to the high surface tension of water, drying the water is affecting my surface area and porosity. So I  have introduced a solvent washing step, where I try to replace water by ethanol using ethanol washing, as the surface tension of ethanol is quite low.
So I am hoping that when I replace water by ethanol, the morphology of my particles will be improved.

I need to measure how much water has been effectively replaced by ethanol.CHN analysis is one way to it, but we don't have that in our lab.

Is there any other relatively simple way in which I can do this?

Thanks for assisting


texts:
What are the factors to consider when predicting the EPR spectrum of $\ce{Cu(Ox)P(CH3)3}$ where $\ce{OX}$ is the oxalate ion?

I understand that there are several factors to consider for EPR (Electron Paramagnetic Resonance) when we have transition metal complexes like: coupling, anisotropy, high spin/low spin, Jahn Teller distortion, Zero Field Splitting, or Kramer's rule. My question is which of these are important for this special copper complex and why?


texts: Determining the temperature at which 90% of the reactants in a equilibrium have reacted

texts:
I have the following problem I am stuck on, specifically the last bit (iii). The first parts are fairly trivial and I have arrived at the following equation to determine the temperature:

$$T=\frac{\Delta H}{\Delta S - R \ln K}$$

However I am unsure on how to proceed. I do not have a value for $K_p$ and I can't think of how to deduce it. I have tried the following, by assuming that
$n_{\ce{Fe3O4}}=n_{\ce{CO}}$, going to the following expression

$$K = \frac{(0.9 x)^3 (0.9 x)}{(0.1x)(0.1x)}$$

but obviously that doesn't cancel.

Any help? I'm probably barking up the wrong tree with the above expression as I'm aware I'm looking for $K_p$ in terms of partial pressures but it would surely result in the same overall problem.

Thanks.


texts:
Can someone explain me whether a protein (like an antibody) would bind to carbon? The carbon arises due to electron beam induced deposition of Polyethylglycol (PEG). The carbon molecules that arise are either due to the PEG that dissociates or due to molecules, that are present in the microscope chamber as contamination, that fall apart. I am thus not sure about what the carbon molecule is specifically. You can look in this experiment to see more of the procedure.

And why? (what bond?)


texts: How can water below a pH of 7 still be alkaline?

texts:
Alkalinity is a measure of the water's ability to neutralize acidity and is expressed in levels of bicarbonates, carbonates, and hydroxides.
How can water that is slightly acidic, e.g. 5.5-6.5, still boast any alkalinity? Or put another way, is there a maximum level of alkalinity for  water at any given acidic pH?
This is based on my understanding that acidity is, put simply, when there are more H+ than OH- ions. So why don't all carbonates react with the surplus H+ ions at pH ranges 5.5-6.5 until either alkalinity is 0 or the pH has reached a neutral 7?


texts:
Is there a general way to predict products of a chemical reaction, given only the atomic masses of masses of all elements involved? for example:

$\ce{CuFeS2 + O2->}$
$\ce{K2CrO4 + H2SO4->}$
$\ce{FeOCr2O3 + K2CO3 + O2->}$
$\ce{K2Cr2O7 + H2SO4->}$

If there's no method to do so, are we supposed to memorize all chemical reactions?

PS: In case you are writing the mechanism of chemical reactions, please bear in mind that products are not known beforehand.


texts: The best chromatographic technique to analyse a solution of benzene, toluene, and ethylbenzene in n-hexane

texts:
What is the best chromatographic technique to analyse a solution containing benzene, toluene, and ethylbenzene in n-hexane?

Is gas chromatography (GC) the best way to analyse this solution? Or is using liquid chromatography with a non polar eluent and column better than GC in this case?


texts: Use chlorophyll a Galvanic cell to create hydrogen and electricity

texts:
What if we want to take chlorophyll in a container and put it into light . Then chlorophyll will lose electrons and will become positive itself then we will have a solution of negatively flowing electrons and positively charged chlorophyll molecules.

But somehow we have to lose electrons and transfer them somewhere so what we can do is take a Galvanic cell and directly  place a wire between the solution and copper rod . Then maybe electrons can get transfer from chlorophyll solution to Galvanic cell and the Salt Bridge between Copper and zinc rods neutralize the solution .

Then once the chlorophyll becomes completely positively charged and electrons have transferred we will put water into it then the electrons from H2O will be gained from chlorophyll molecules and H2 will get separated into h+ two molecules and one molecule of o . Two molecules will form oxygen and get released into the air while h+ and will remain in the solution.

Then we will take another container with chlorophyll that has been put into the light and we will connect wire between these two chlorophyll solutions and electron from the the second container will flow to the first container and H + ions will get converted to H2 gas and we will capture this gas and will use all the electricity flowing between.

Will this method work?


texts: How to separate sodium iodide dissolved in water?

texts:
Am fairly new to chemistry and apologize if the question and the description are too vague.If you think I lack basic background knowledge to deal with something like this, please point me to a resource, a book or anything that can help me in this regard. So in case this question is off-topic, please suggest where I should begin- at least starting point for my research will be helpful. However, in that case, if possible, please be specific, cause its too much of an effort to read entire chemistry textbooks to find out the answer to this one question.

Would like to know how to seperate NaI dissolved in water. Please suggest a way to do so without heating and evaporation. Like, what compound should I add to the solution so that the NaI can react with that resulting in solid products, maybe in the form of lumps/signicantly sized suspended particles that can be easily filtered out.

Additionally I would like to know how to find out, given a solvent (or any liquid compound), whether NaI dissolves in it or not. For eg: say that I have methanol, will NaI dissolve in it? For methanol i know the answer and its a yes. But how do i test solubility for any other compound. Of course chemists should not have to carry out practical experiments to find out this(it must probably be part of a known set of facts(about a particular compound) to chemists or they will be able to deduce it from some other known facts. How will a chemist answer this question?)

And finally, once I have any solution with NaI dissolved, how to separate it without evaporation(but by some chemical reaction). For eg: how to separate NaI from methanol? how to figure out the reactants I'll need in case the solvent is known?


texts: Donation by inductive effect and withdrawal by conjugation

texts: Is there a group that would attached to a benzene ring, donate electrons by inductive effect and withdraw them by conjugation?


texts: Stereoselective enolate formation with different bases: Does the addition of a base NR3 to a ketone affords the cis or the trans enolate?

texts:
I'm wondering if the addition of a base of type $\ce{NR_3}$ (R: alkyl) to a ketone (e.g. 3-pentanone or 4-heptanone) results in the cis or trans-enolate.

I'd like to ask here about four cases:

$\ce{NMe_3}$ (small)
$\ce{NMeEt_2}$ (medium)
$\ce{NEt_3}$ (big)
$\ce{N(iPr)_2Et}$ (very bulky)

Maybe smaller bases as 1 or 2 usually give the trans-enolate, and bulkier bases such as 3 or even 4 affords the cis-enolate. (That's what I read, but I'm not able to understand why.) Is there a good explanation that rationalizes which enolate is formed, the cis or the trans?

Sterically hindered bases forms the the kinetic enolate. For deprotonation of 3-Methyl-4-heptanone I assume the enolate at the linear unbranched chain site, that's clear for me, but kinetic/thermodynamic enolate has nothing to do with cis/trans enolate or does it?

Related:
Does the addition of base to 3-pentanone give the cis or trans enolate?


texts: Mechanism of Hofmann Rearrangement Reaction

texts:
In the Hofmann Rearrangement Reaction (in basic medium), when $\ce{RNH-}$ ion is produced, why does it not attack $\ce{Br2}$  or take $\ce{H+}$from the amide itself?
Also, why does it take $\ce{H+}$ from water only?


texts: Electrophilic aromatic substitution of napthalene

texts:
It is known that the $\alpha$-position (or 1-position) for napthalene is the preferable position for substitution to occur at. However, I am getting two different explanations as to why this is the case, one of which I am not able to make sense of.

The first explanation which I have come across and which is also the one I am able to make sense of is given by Hepworth, Waring and Waring (2002). They explain it by using the concept of Clar's rule. With an attack at the $\alpha$-position, there would be two resonance structures in the intermediate with preservation of the aromatic sextet. With an attack at the $\beta$-position, there would only be one resonance structure in the intermediate with preservation of the aromatic sextet. As such, the $\alpha$ attack would be more preferable since the resultant intermediate would be more stable.

The second explanation which I have come across just today comes from Carey and Sundberg (2007). An image of the section of the text discussing the issue is shown below.

I am not able to understand why they have mentioned that the intermediate resulting from $\beta$ attack is not under allylic stabilisation because it seems to me that it is under such stabilisation, after drawing out the resonance structures. I would like to clarify if this explanation is accurate.

References

Carey, F. A., & Sundberg, R. J. (2007). Advanced Organic Chemistry Part A. Structure and Mechanisms (5th ed.). Springer.

Hepworth, J. D., Waring, D. R., & Waring, M. J. (2002). Aromatic Chemistry. United Kingdom: The Royal Society of Chemistry.


texts: Euler's Theorem and Extensive properties

texts:
I read in a textbook (Mathematics for Physical Chemistry by D. McQuarrie) an example of Euler's Theorem used in Thermodynamics. The author states "The [variables] are all extensive [quantities], and so [Euler's theorem is applicable]" (I'll provide more details below)

My question: why do variables being extensive indicate that this theorem is relevant?

The theorem starts by stating that a function is homogeneous to degree $N$ in some set of variables if those variables always form terms such that their powers sum to $N$. For example:

$f(x,y) = yx^2 + y^2x + \frac{y^4}{x} + x^3$

that would be homogeneous degree 3 for $x$ and $y$.

The theorem concludes with:

If $f(\lambda x,\lambda y) = \lambda^N f(x,y)$

Then $Nf(x,y) = x\frac{\partial f}{\partial x} + y\frac{\partial f}{\partial y}$

This
is the wikipedia page for the same theorem.

The example uses the above theorem to derive:

$U = S(\frac{\partial U}{\partial S})_{_{V,n}}+V(\frac{\partial U}{\partial V})_{_{S,n}}+n(\frac{\partial U}{\partial n})_{_{S,V}}$

The author's solution immediately states: "The entropy, volume, and number of moles are all extensive thermodynamic quantities, and so $U(\lambda S,\lambda V,\lambda n) = \lambda U(S,V,n)$." After that statement the solution is simple.

I know that extensive variables means that they scale with the size of the system, but the relation to this theorem is unclear to me. I suppose that if the system is "twice as big" ($\lambda$ is doubled), then energy, entropy, volume, and amount are doubled. That still seems vague to me if its even a good way to think about this.

Thank you.


texts: Acidic nature of boric acid when its concentration high

texts:
Following statement was given for boric acid $(\ce{H3BO3}):$

  At low concentrations $(\leq\pu{0.02 M})$ essentially $\ce{B(OH)3}$ and $\ce{B(OH)4-}$ are present, but at higher concentration the acidity increases and pH studies are consistent with the formation of polymeric species such as $$\ce{B(OH)3 <=> H+ + [B3O3(OH)4]- + H2O}$$

Please explain the meaning of the italicised statement i.e. pH studies are consistent with the formation of polymeric species?


texts: What is the oxidation state of Calcium in teeth?

texts: What is the oxidation state of Calcium found in human teeth?


texts: What is the Lewis structure of the azide ion?

texts:
On a chemistry homework, we're asked to draw the Lewis structure of  $\ce{N3-}$.

My answer:

Nitrogen ordinarily has five electrons in its valence; $\ce{N-}$ has six. This makes a total of 16 electrons overall.
If we place the negative charge on the central atom, we get a structure of $\ce{N=N^-=N}$

This has a formal charge of $(-1)$ on each of the side nitrogen atoms and $(2)$ on the central nitrogen atom once you've accounted for the extra electron, so the formal charges cancel out only when you account for the added electron.

This answer is supported by a bunch of online sources (1, 2).

Homework software response:

The correct answer is $\ce{N#N+-N^2-}$

That's all it says. My understanding of why this is valid is that this gives a formal charge of $(0)$ for every atom, as opposed to averaging out to that.

I suppose the second form makes sense, as it's a lower formal charge on the central atom. If so, why do online resources prefer the first? Is there some resonance going on here, and the actual structure has bond orders of $\frac52$ and $\frac32$?


texts: What is the diagram of the roto-inversion of $\bar 6$?

texts:
Using the standard way of representation:

Here we have a rotation followed by an inversion (technically called 'rotational inversion'). So as to represent it, what I have done is:

1) Both rotation and inversion occur for the first time. The circle changes of plane:

2) Both rotation and inversion occur for the second time. The circle changes of plane again:

My issue is that I am not convinced of this, because in theory there is rotation followed by an inversion and they do not happen simultaneously. So if this is wrong, what is the correct representation and why?

Diagram for $\bar 3$

Diagram for $\bar 6$

METHOD:

NOTE: I have used comma to stress there was an inversion

Thank you


texts: Chemical or simply a physical reaction? coca cola + liquid propane

texts:
In this video what is that creates the propulsion of the bottle? Is it a chemical reaction or simply a state change?
https://m.youtube.com/watch?v=VxvJcPToXb0

I think is the propane that passes from liquid to gas, nothing more.


texts: On the activity of liquids and solvents in equilibium constants

texts:
This is a confusion I've had for quite sometimes, first when learning about equilibria (due to contradicting teachers), then when trying to teach it (due to contradicting sources, in books and on the Internet).

When facing an equilibrium (let's be original and take $\ce{a A + b B <=> c C + d D}$ as an example), the equilibrium constant is
$$K = \frac{a(\ce{C})^c \cdot a(\ce{D})^d}{a(\ce{A})^a \cdot a(\ce{B})^b}$$
where $a(\ce{X})$ is the activity of X.

For pure solids, the activity is 1; therefore solids "do not appear" in the expression of the constant.
For dilute solutions, the activity of the solute can be taken as its molar concentration. Thus, supposing A, B, C and D are not solids, the equilibrium constant can be written as

$$ K_c = \frac{[\ce{C}]^c [\ce{D}]^d}{[\ce{A}]^a [\ce{B}]^b}$$

But what happens when facing liquids (e. g. water)? In that case, I have seen two things :

Just putting the "concentration" of the liquid into the equilibrium constant.
A pure (or nearly pure, such as the solvant in a dilute solution) liquid has an activity of (or nearly of) 1. Therefore, the liquid should not appear in the constant.

Let's apply both cases to acidity constants, for the reaction $\ce{HA + H2O <=> A- + H3O+}$.

As $[\ce{H2O}] \approx 55.55$ mol/l in dilute solutions,
$$K_c = \frac{[\ce{A-}][\ce{H3O+}]}{[\ce{HA}][\ce{H2O}]}
\textrm{ and }
K_a = \frac{K_c}{[\ce{H2O}]} = \frac{[\ce{A-}][\ce{H3O+}]}{[\ce{HA}]}$$
As $a(\ce{H2O}) \approx 1$ in dilute solutions,
$$K_a = K_c = \frac{[\ce{A-}][\ce{H3O+}]}{[\ce{HA}]}$$

Which way is correct? I'd be more inclined to follow the option #2, but I've been stared at wide-eyed like a heretic when talking about that.


texts: Calculating conductivity of a solution given molar conductivities and concentration

texts:
From my understanding the conductivity of a solution ($K$) is given by the sum of the conductivities of ions in solution:

$$K = c(K_{m,1}+K_{m,2})$$

Where $c$ is the concentration, and $k_{m1}$ and $k_{m2}$ are the respective molar conductivities of the two ions. For example, with a solution of $\pu{0.1 mol L-1}$ $\ce{NaOH}$:

\begin{align}
K &= 0.1(K_{m,\ce{Na+}} + K_{m,\ce{OH-}})\\
K_{m,\ce{Na+}} &= \pu{50 S cm2 mol-1}\\
K_{m,\ce{OH-}} &= \pu{197.9 S cm2 mol-1}\\
K &= 0.1(247.5)\\
K &= \pu{24.75 S m^-1} (?)
\end{align}

However I think the units are throwing me off here as my calculations aren't making much sense - I was led to believe the conductivity was much lower.

Could you please offer some help with these calculations?


texts:
I am in need of help for my understanding in specific heat capacity. To be honest, I understand the lesson effectively, However, just a few days ago, I've encountered two similar yet different-in-approach problems. Here are the problems:
1.) A sample of gold was dropped to a glass of water. The water had a given initial temperature that was higher than the gold. Eventually, a final temperature for both elements were given. The problem was asking for the mass of the gold?

The solution showed to me that the heat of the gold (qgold) released is equal to the heat of water (qwater) absorbed.

qgold = -qwater

Now, I can see that the glass which served as the container of the water was not included in the equation. As far as I can get the logic of this, the second problem seemed to have a different approach but this time the container is involved in the heat transfer. Now this is the second problem:

2.) An unknown sample with a given mass and given initial temperature was dropped to a can with water. The can and the water had a similar initial temperature, but the two had a different mass. The final temperature of all elements present in this problem was given. The problem was asking for the specific heat of this unknown sample. The thing is, this is the part where I am a bit confused because the solution given to me was this:

q of unknown substance = q of the can + q of water

Now, what I really want to ask is this: When do I consider including the heat of the container of the system in this type of problem, as it is very situational in this case? My professor told me it's about material thing. However, I seem to not deem my professor's explanation to be sufficient, for I know a better explanation could be given.

I hope I would get a very comprehensive reply as soon as possible.

Thank you!


texts: Sonication to purify solid product- the crude product just disappeared

texts:
I am forming Fmoc-valine-citrulline dipeptide, and below is the literature protocol I am following (from Bioconjugate Chem 2002, 13 (4), 855-869):

Formation of Fmoc-Val-Cit

Fmoc-Val-OSuc (succinimidyl ester) ($\pu{14.91 mmol}$) in DME ($\pu{40 mL}$) was added to a solution of Cit ($\pu{2.743 g}$, $\pu{1.05 equiv.}$) and NaHCO3 ($\pu{1.315 g}$, $\pu{1.05 equiv.}$) in water ($\pu{40 mL}$). THF ($\pu{20 mL}$) was added to aid solubility, and the mixture was stirred at room temperature for 16 h. Aqueous citric acid (15%, $\pu{75 mL}$) was added, and the mixture was extracted with 10% 2-propanol/ethyl acetate ($\pu{2 \times 100 mL}$). The solid product began to precipitate but remained in the organic layer. The suspension was washed with water ($\pu{2 \times 150 mL}$), and the solvents were evaporated. The resulting white solid was dried in vacuo for 5 h and then treated with ether ($\pu{80 mL}$). After brief sonication and trituration, the white solid product was collected by filtration

I confirmed the formation of the crude product through HRMS and NMR. I then proceeded to carry out sonication to purify. I thought the purpose of sonication was to initiate crystallization. However, when I sonicated the crude product (~20 mins), I observed that the product was well-dissolved in ether, rather than forming a crystal. I used a Büchner funnel to collect the product but there was nothing left on the filter paper. Would pouring more slowly over the filter paper solve the problem? And more importantly, I want to understand the purpose of sonication step.


texts: Can running water carry an electrical current indefinitely, and for long distances?

texts:
Okay, not a scientist, but doing a writing project that requires a little knowledge. My question is: If there's a constant source generating enough energy into running water (like a stream, surrounded by non-conductive material) could the water carry an electrical current for an indefinite period? Basically, doing the same job as a wire.

I think the conductors in the water (minerals) may deplete over time because of chemical reactions to this process...but if it's a running stream with constantly renewed minerals, could this happen?

Edit: Clarification was requested for a couple parts. 1) Method of conduction to the water: Not that important, really. I guess a wire capable of conducting the necessary amount of power could work. 2) How fast the water flows: I'm not sure. A strong currant, I guess. But not as severe as rapids.


texts: Why does the hydroxide ion have a negative charge?

texts:
I've been studying the roles of hydroxide & hydronium in acids and bases, and it was mentioned that a hydroxide ion (OH-) has a negative charge. Can someone give me a layman's explanation of what causes this charge?

Since hydrogen and oxygen are sharing a covalent bond, is the charge negative because an electron is donated from oxygen, thus giving hydrogen 2 electrons?


texts: For group 7 elements, are anions a lower energy state than being neutral atoms?

texts: Given that electron affinity is positive, why don't these atoms attract free electrons and "prefer" to exist as anions?  Never made sense to me — I could be missing something obvious.


texts: I'm looking for a solvent which can fully dissolve dried aloe vera gel. I assume the main problem is the constituent polysaccharides.


texts:
I have a drawing of a molecule, I want to know its name. Is there a software, or website that can help me identify the chemical? Im not a chemist, its been a decade since I had chemistry in college, and I cannot simply guess the name of the chemical.

The model goes like this:
C4H9-Benzine-N=CH-Benzine-CH=N-Benzine-C4H9

(also if there is a simpler form of this molecule, Im not sure how to simply it) I'm hoping It is a known chemical and that I can get details about it.


texts: How do thermodynamics and kinetics control this reaction?

texts: The answer is A, but how is that? I know B is an intermediate, so that after short time it will be bigger than C, but what does "thermodynamic control" and "kinetic control" mean?


texts: Can iproniazid be prepared by reacting isoniazid with 2-chloropropane?

texts:
I'm asking as I fear that the 2-chloropropane might react with the pyridine ring to form k-isopropylpridine-4-carbohydrazidine where k=2,3,5. Or that no reaction will take place.

Figure 1: Isoniazid

Figure 2: Iproniazid

Figure 3: 2-chloropropane


texts: Why does water dissociate to H3O+ and OH- rather than H+ and OH-?

texts:
Why does water dissociate to
$\ce{H_{3}O^{+} + OH^{-}}$
instead of $\ce{H^{+} + OH^{-}}$?

This question came to surface when I was learning about acids and bases, and learned this definition:

$\mathrm{pH=}-\log_{10}[\ce H^{+}]$

Which after looking at wikipedia, looks like a simplified definition, but it got me thinking - how can water have a pH of around seven if it dissociates into $\ce{H_{3}O^{+}}$ instead of $\ce{H^{+}}$? Why does it do this instead of the expected dissociation?


texts: Why add specifically hot solvent during recrystallization procedures instead of heating it up after?

texts:
Recrystallization methods that I have seen online and in manuals involve adding a minimum amount hot solvent to the solid mixture. Is there a reason I should do this instead of adding an equivalent amount of solvent at room temperature and then heating?

I've tried dissolving table salt and sugar both ways, but I didn't notice a substantial difference other than adding hot solvent directly requires less time to dissolve because it took time to heat the cooler solvent.


texts: The difference between peptide bonds and the bonds between polypeptides?

texts:
I was doing some tests for the multiple-choice final we've got ahead. And it was on me to count the peptide bonds in an Insulin hormone with 51 aminoacids arranged in two polypeptides with 30 and 21 aminoacids. (these are not true in reality) the number of bonds were 49, not 50, and that means the bond between two polypeptides doesn't count as a peptide bond. Additionally, I know that polypeptide bonds make the proteins' molecular structure, as it is now. (just look at that shape.) PEPTIDE COVALENT BONDS CAN NEVER cause that kind of 3d orientation in space. So there must be some fundamental difference between those bonds. What is it?
 My research couldn't find any results as simple things have jammed the internet.


texts: Optical Isomerism in Coordination Compounds of type MA₂B₂(CC)

texts:
I was asked the following question:

How many optical isomers are there for $\ce{[Cr(NH3)2Cl2(en)]^+}$ ?

First of all I figured out the following four geometrical isomers of the above complex:

Out of which, (iii) and (iv) are optically inactive, due to a plane of symmetry (shown by faint line) passing through them as shown below:

For (iii), you can suppose: green as $\ce{en}$, orange as $\ce{NH3}$ and red as $\ce{Cl}$. Similarly, for (iv), you can suppose: green as $\ce{en}$, orange as $\ce{Cl}$ and red as $\ce{NH3}$.
Therefore only (i) and (ii) will show optical isomerism, which I've confirmed myself.

But, the following four isomers was provided as answer, in which I don't think that the second configuration of complex will show any optical activity due to plane of symmetry (as discussed above for the (iv) geometrical isomer).

What I am doing wrong?


texts: What are these upside-down glass egg-shaped containers for?

texts: I took this picture from a chemical vendor, but I've seen these things many times already. How are they called and why are they upside-down?


texts: Safe coating to make a 3D printed respirator mask airtight

texts:
What is a good example of something safe that could be applied as a coating layer to the walls of a 3D printed respirator mask to make them truly airtight (seal pores and fissures) while (ideally) satisfying the following criteria?:

Not air permeable at the pressures created when a person inhales
No (or low) VOC out-gassing from the coating
Does not impose health risks to the respirator wearer
Can be applied by dipping (or maybe spraying)
Forms a thin layer that is flexible enough not to crack during normal use of the mask

Here are some materials I have been considering for the job:

White glue (school PVA glue): Seems safe. Is is airtight?
Water based liquid rubber: some SDS suggest it's safe. It's marketed as watertight (but is it AIRtight?)
Some sort of common paint?

If someone here could suggest some potential coating materials or knowledge bases where I could check their non-permeability/safety, I would be really grateful.

As I'm not a native speaker, I apologize for any broken grammar.

The problem: It is well known that 3D printed objects are usually not exactly airtight, due to micro-fissures. To make things worse, I ordered a DIY 3D printed respirator mask (composed of ABS plastic) that is visibly permeable to air (one can literally see the tiny gaps all across it's walls' surfaces through which air and viruses could come in when the wearer inhales).

P.S.: Silicone caulk might not be an option, since it's too viscous and would be a mess to apply to the outside of the respirator, rendering an unprofessional finishing. I should note that I could possibly apply it only to the inside of the walls, but I intend to coat all surfaces, just to be extra safe.


texts: Why does the SCF not converge in a structure optimization with GAMESS of the thiourea molecule at the PM6 level of theory?


texts: Why does freezing point decrease when vapour pressure decreases in dilute solutions?

texts: I was studying colligative properties of dilute solutions, and one of the properties was freezing point depression. The confusion I had was that, if vapour pressure decreases, it should be easier to reach the freezing point (point where vapour pressure of solid and liquid are equal). So I thought the freezing point will increase, but freezing point actually decreases. Is there any logical explanation?


texts: Stoichiometric calculation of composition of a compound

texts:
I have a question from a high school review package. I don't need the answer, but one thing that is bugging me is that, I feel as if I do not understand the question at all. I don't know what it wants me to find.
Can anyone please tell me what the question is about?
The question is:

Copper oxide is a black powder. It can be decomposed by heating it with an excess of charcoal, a form of carbon.
The charcoal reacts with the copper oxide to produce copper and carbon dioxide. Any excess charcoal that was used can be separated from the copper by adding water. The charcoal will float on the water while the more dense copper will sink to the bottom. The charcoal can then be skimmed off.
Mass of copper produced = $\pu{2.76 g}$
Mass of copper oxide used = $\pu{3.45 g}$
a) Use this data to determine the simplest formula of copper oxide.
b) Predict the valence/charge of the copper in the copper oxide formed.

I basically got:
$$\frac{2.76}{63.546} = \pu{0.043 mol}$$
The balanced chemical equation that I deduced was $$\ce{2CuO + C -> 2Cu + CO2}$$
However, I am not sure that my understanding of the question is correct. Is there a mistake in my understanding.
Note: I was able to solve the question.


texts: Why is it important to minimize impurities when doping a semiconductor?

texts:
I was reading "Electronic Devices and Circuits" by Boylestad, and in there the author talks about how the semiconductor industry seeks to add as little impurities as possible when manufacturing semiconductors.

What I don't understand is why it is so important to keep the material's purity? What characteristics are improved by doing that? If the objective of doping is improve the conductivity of the material (in a controlled manner), wouldn't reducing the ammount of doping material decrease that efficiency?


texts: Specifically how dangerous is a 10g chemical sample of pure arsenic and how do you properly dispose of it?

texts:
I'm not a chemist.  I'm an electrical engineering student and I recently purchased an element collection.  The collection came with a 10g arsenic sample.  I assumed it wasn't much of a thing because there were no warnings or anything but afterward when I started reading more I became concerned.  How dangerous is the really, what precautions must I take in handling the sample, and most importantly how do I properly dispose of this sample?

Thank you


texts: Calculating the ionic strength of a histidine solution

texts:
I'm trying to repeat the calculation of the ionic strength of a solution containing histidine as a buffer I recently read in a paper. In their paper, the authors calculate the ionic strength of a 20 mM solution of histidine at pH 5.8 to be 7.7 mM. They also state that the average charge of Histidine at this pH is equal to + 0.61.
For my calculation I used to Henderson-Hasselbalch equation to calculate the distribution of charged species at the pH specified,
pH = np.arange(0.1, 14, 0.001)

def macroscopic(pH, pka1, pka2, pka3):
    return ((-1)**2 + 0 * 10**(pka1 - pH) + (1)**2 * 10**(pka1+pka2 - 2*pH) + (2)**2 * 10**(pka1+pka2+pka3 - 3*pH)) / (1+10**(pka1 - pH) + 10**(pka1+pka2 - 2*pH) + 10**(pka1+pka2+pka3 - 3*pH))
def DDD(pH, pka1, pka2, pka3):
    return 1 / (1+10**(pka1 - pH) + 10**(pka1+pka2 - 2*pH) + 10**(pka1+pka2+pka3 - 3*pH))
def PDD(pH, pka1, pka2, pka3):
    return 10**(pka1 - pH) / (1+10**(pka1 - pH) + 10**(pka1+pka2 - 2*pH) + 10**(pka1+pka2+pka3 - 3*pH))
def PPD(pH, pka1, pka2, pka3):
    return 10**(pka1+pka2 - 2*pH) / (1+10**(pka1 - pH) + 10**(pka1+pka2 - 2*pH) + 10**(pka1+pka2+pka3 - 3*pH))
def PPP(pH, pka1, pka2, pka3):
    return 10**(pka1+pka2+pka3 - 3*pH) / (1+10**(pka1 - pH) + 10**(pka1+pka2 - 2*pH) + 10**(pka1+pka2+pka3 - 3*pH))'''

Where the values of pKa1, 2 and 3, used by the authors, are equal to 9.17, 6.0 and 1.82 respectively.
I then calculate the ionic strenght of the solution according to
def ionicstrength(pH, pka1, pka2, pka3):
    return 0.5*(DDD(pH, 9.17, 6.0, 1.82)*BuffermMConc*(-1)**2 + PDD(pH, 9.17, 6.0, 1.82)*BuffermMConc*(0)**2 + PPD(pH, 9.17, 6.0, 1.82)*BuffermMConc*(1)**2 + PPP(pH, 9.17, 6.0, 1.82)*BuffermMConc*(2)**2)
#def averagecharge(pH, pka1, pka2, pka3)

where the variable BuffermMConc is equal to the mM concentration of the buffer, in this case 20.
When I plot the results I get the following graph,

Where the dashed line represents the ionic strength and the coloured lines the distribution of histidine species. For pH 5.8 I obtain an ionic strength of 6.13 mM, which compares to the ionic strength of 7.7mM determined by the authors. The authors also report the average charge of histidine, which is identical to the value I determined. This would indicate that the distribution of charged species is probably correct in my calculation. I cant  figure out why my ionic strength calculation is different.
Any help would be greatly appreciated.


texts: Why is temperature considered as an important factor in deciding chemical reaction kinetics?

texts:
According to the Arrhenius equation, the rate of reaction is proportional to $e^{-1/RT}$.

Here is a plot of the equation and its derivative with respect to temperature, both with respect to temperature. All constants are set to unity.

It seems to suggest that there is almost no change in the rate of reaction with increasing temperature except at very-low-temperature range.

Then, why is temperature considered an important factor in deciding the kinetics of a chemical reaction?


texts: Can precipitation occur in states of matter other than liquids?

texts:
This answer to Are precipitation and crystallization both analogous between chemistry and meteorology? discusses the history and use of the term "precipitation" in chemistry.
From what I remember in school I was introduced to precipitation in the context of reactions in liquid media and usually water.
In meteorology the term refers to a phenomenon in air where droplets or crystals form from some molecules mixed with others. I don't know if we can call the nitrogen/oxygen mix a solvent and the water vapor the solute, but some of the resulting droplet suspensions are indeed called aerosols.
But my question here is constrained to chemistry. Do we speak of precipitation in media other than typical liquids? Are there gaseous precipitations? Are there precipitations in supercritical situations? Do they happen in glasses or in (presumably pretty hot) solids?


texts: Antibonding, Nonbonding and Bonding orbitals

texts: Recently I came across nonbonding orbitals. I know something about bonding and antibonding orbitals and their formation, but I have no idea about nonbonding orbitals. Could someone explain their formation and the difference when compared with the other two?


texts: Removing Heavy Rust from Very Old Carbon Steel Carving Knife on the Cheap

texts:
I am trying to remove heavy rust from a carbon steel 10-inch carving knife. Mothers Polish did not get rid of much of the rust. I turned to vinegar soaking and scrubbing: At first it took off a good bit of the rust leaving visible residue in the bottom of a glass carafe. With a lot rust left I turned to vinegar and salt (see below). I have been soaking the knife using this solution in the 1-quart glass carafe for three or four days. Every day I pull out the knife and scrub it vigorously with a wire brush. Lots of black stuff comes off on a paper towel but there is still a lot of stubborn rust. When I take the knife out of the carafe the knife is blacker then when I put it in. After a vigorous wiping an alligator-like pattern remains on both sides.
I am using the same solution daily without changing it save for topping off the carafe. Also there seems to more chemical activity going on at the top of carafe than at the bottom, for some reason: is there an explanation of the phenomena?
If the rust is indeed being dissolved slowly I am wondering if the solution is loosing potency? Is the stoichiometry changing as the rust is being removed? Would changing the solution daily/ frequently help speed this process? Would frequent stirring help uniform the gradient? Is there a better method using household products?
I do not want to resort to expensive OTC cleaners or high-end sandpapers. Oh! FYI: pun intended-I am many decades rusty in Organic and Physical Chemistry.
Thanks for any thoughts.
Source of the idea: Hunker....Fill a large container made of a non-reactive material, such as plastic or glass, with 1 gallon of distilled white vinegar. Add 1 cup of table salt and stir the mixture to combine. The salt will increase the potency of the acid in the vinegar, making it even more effective. Use 1/2 gallon of vinegar with 1/2 cup of salt for smaller objects


texts: SN2 vs SN1 in Acidic Environments for Secondary Alkyl Halides

texts:
I have researched three books: Brown's, Solomons' and Wade's. I could not find enough information about this.

My prof. says that secondary alkly halides undergo SN1 only under acidic environments.

We had this quiz. I got a terrible mark on one question.

I think these are the missing structures.

Now, I am wondering, did Sn2 occur here, if yes, at what rate? Was it more important than Sn1? What was the major pathway?

What is the major pathway for all secondary alkyl halides with acidic environment and with NONacidic environments?

Could anyone also just check my missing structures?


texts: Why does alcohol crack acrylic (plexiglass)?

texts:
I have seen videos and discussions about alcohol cracking acrylic, and waterblock manufacturers reminding users to not use alcohol in cooling systems with plexiglass acrylic, but why is this so?

The question proposed as duplicate only asked for the effect, but here I already know the effect. I am asking for the reason for the effect, which is not answered in the answer to the 'duplicate' question.


texts: Why does pouring carbonated beverages onto fruit cause them to fizz?

texts: I have noticed that making mimosas, the champagne fizzes more than just pouring it into a flute. Likewise, pouring beer onto citrus fruit or strawberries fizzes a lot. My theory is that the pH drop associated with the acidic fruit causes the solubility of CO2 to decrease and hence, the fizz. Can anyone verify this?


texts: Relationship between the first and the second quantum number

texts:
Does the secondary quantum number tell how many subshells a specific principal quantum number shell has?

E.g., if the principal quantum number is $n$, there are ($n-1$) subshells.


texts: How do I get the smell of Febreeze (uncomplexed cyclodextrin composition) out of my carpet?

texts:
Help! I sprayed my old carpet, which had gotten a little mildewy from some wet towels left on it, with Febreeze original scent. Now I can't get that horrible scent out! It might also be mixed with some newly formulated Nature's Miracle which I sprayed on the couch above the carpet at the same time, but I don't know the chemical formula for that.
I have  tried the following: white vinegar in water, vodka in water with some grapefruit essential oil, bleach solution in water, Concrobium Mold Control spray (I can still smell the sour mildewy smell...or is that the vinegar?), ZEP Mold Stain and Mildew Stain remover, Folex carpet spot remover, baking soda, corn starch, vacuumed up the last two as best I could...
So my question is, what next? Hydrogen peroxide? Isopropyl alcohol? Unscented dishwashing detergent? I don't want to layer on any more scents, god forbid, in an attempt to get rid of this fake flowery sour smell. (Someone described the Nature's Miracle scent as making their cat smell like "candy-coated skunk." I think the Febreze might have bonded to the Nature's Miracle...)
I would enjoy understanding the science of this too!
My research so far online says that Febreeze cyclodextrin is cup shaped and surrounds smelly organic molecules, but doesn't break them down. And the scent that's added to the cyclodextrin is re-released through heat, so steam isn't recommended. And I'm a renter and I doubt my landlords will replace the carpet.
Thanks!
Annette


texts: Density calculation with cubic equation of state

texts: I want to calculate the density of CO2 using a cubic equation of state in order to plot the P-v diagram. From theory I know that I get one real root when the substance is in single-phase region and two when it is in two-phase region. In the latter case the smaller volume is associated to liquid while the other to vapor. I'm using Matlab to solve the cubic eos, incrementing the pressure and the temperature at fixed intervals.  How can I merge the two solutions to represent the actual Pv plot?


texts: Permanganate oxidation of side chains in Benzene Derivatives

texts: What is the exact mechanism of permanganate oxidation of side chain derivatives of benzene? Is it same for all functional groups? I want to know that in any situation I mean when side chain has only one benzylic hydrogen gives the carboxylic acid. Why does it occur?


texts: Miscibility of Hexane and Ethanol (Anhydrous vs 96%)

texts:
In my lab, I mixed 8:2 (mass:mass) of Hexane:Ethanol

(Hexane: 0 ppm of water content, analytical grade, & ethanol: 4% water content, pharmacy grade)

At room temperature, and at -20ºC, there was a clear phase separation.

I repeated the experiment, but using anhydrous ethanol instead (1300 ppm of water content).

Now, at room temperature, and at -20ºC, there was no phase separation.

I added enough water to the mixture to make it equal to the first mixture, and the phase separation came clearly into view.

My question is, is this kind of very specific data of miscibilities available somewhere? Ethanol 96% is what is commonly used, yet pure ethanol behaves differently in this case.

Any link or insight into the importance of such little water is appreciated.


texts: Why is H2SO4 a good dehydrating agent while other strong acids are not?

texts: I understand that $\ce{H2SO4}$ is a very good dehydrating agent because it is a strong acid, so that it quickly donates $\ce{H+}$ to hydroxide ions in water to form $\ce{HSO4-}$ and $\ce{H3O+}$ .But we know that there are a lot of other acids stronger than $\ce{H2SO4}$ like $\ce{HClO4}$ which are not used as dehydrating agents. They can also readily give $\ce{H+}$ to hydroxide ions in water and act as dehydrating agents but we don't use them for this purpose. Why is that?


texts: How to determine the concentration after a dilution with Beer's law?

texts:
The molar extinction coefficient of pure antibody is $1.4$ absorbance units per milligram antibody at $\pu{280 nm}$. You have a concentrated antibody solution, so you make a $5$-fold dilution and measure at $\pu{280 nm}$, getting an absorbance of $0.845$. What is the concentration of that solution?

Using Beer's Law this is my work:
$$0.845 = (1.4)\cdot (1)\cdot (c) \\
\therefore c = \pu{0.604 mol L^-1}$$

Then I think we need to factor in the dilution, therefore $c = (5) \cdot (0.604) = \pu{3.02 mol L^-1} $. Is this correct?


texts: Synthesis of a tungsten carbene bromide from [CpW(CO)3]-

texts:
I'm currently working through past test and exam papers in order to prepare for my organometallic test at the end of the month, but unfortunately I've gotten stuck on the following question.

Since I don't know how to build molecules on here, I've attached a screenshot of the question.

The biggest problem I have is getting the Br coordinated to the metal while I already have my alkyl $\ce{(CH2CH2CH2Br)}$ bonded to one of the carbonyls. I don't know what reagent to use to get it on there. One idea I have is using $\ce{NaBH4}$ to get a hydride onto Tungsten, then I use R-Br (where R is some alkyl) to essentially swap the H with the Br and form as a by-product, R-H, but I'm not sure if this would work. Below is my complete synthesis.

EDIT: I spoke to my professor and it was unnecessary for me to remove the $\ce{Br-}$ in one of the earlier steps. That $\ce{Br-}$ would've attacked the metal centre later on and the rest of the steps would be elementary.


texts:
a. Explain how overshooting the titration of the aqueous layer (ie. using too large a value for the volume of thiosulfate to react with the iodine and of triiodide ion) would affect the concentrations of iodide ion, iodine and of triiodide ion, and therefore of the calculated $K$.

My thoughts regarding this question
overshooting the titration will increase the concentrations of the iodide ion, iodine and triiodide ion
- According to me  a change in $K$ comes only when the temperature is changed.

  b. Explain how using too large a value for the minimum volume of thiosulfate to react with the iodine (organic) in the mineral oil layer would affect the concentrations of iodide ion, iodine and triiodide ion, and therefore of the calculated $K$

I am unsure of the answer for this one too.
My reasoning
Using too large a value for the minimum volume of thiosulfate will increase the concentrations of the iodide ion, iodine and triiodide ion and nothing will happen to $K$ again.

Is my reasoning correct?


texts: How to find the number of atomic microstates for a given electronic configuration?

texts:
Given some electron configuration, I know the following formula can be used to determine the number of microstates:

$$\text{# mircostates} = \frac{(\text{# electron positions})!}{((\text{# electrons})!(\text{# positions} - \text{# electrons})!)}$$

So for 2 electrons in a $\mathrm{p}$ orbital it would be $6!/(2!4!) = 15$, or for two electrons in a $\mathrm{d}$ orbital it would be $10!/(2!8!) = 45$.

I'm a little confused how to apply this for a situation where all the electrons are not in the same $l$ level.

For a configuration like one electron in $\mathrm{s}$ and one in $\mathrm{d}$ would the number of microstates be the product of the above formula for each $l$ level?

$$\frac{2!}{1!1!}\cdot \frac{10!}{1!9!} = 20$$

Or for one electron in $\mathrm{s}$ and one in $\mathrm{f}$:

$$\frac{2!}{1!1!}\cdot \frac{14!}{1!13!} = 28$$

I assumed it would work like this because the formula reminds me of multiplicity, so it would make sense for it to be a product. But it also occurred to me that the 2 $l$ levels could be combined for the formula, so for a $\mathrm{(s^1)(d^1)}$ electron configuration, the number of positions would be $$\frac{(10+2)!}{2!(10+2-2)!} = \frac{12!}{2!10!}= 66,$$ which is must bigger than what I had before.

Can anyone clear up how to apply this formula to a case like this?

For clarification, the exact specification in the problem was:

  Imagine a $\mathrm{s^1\, f^1}$ electron system (that is, 1 s electron and 1 f electron; no p or d electrons).  How many total microstates exist for this system?

I think this means that the one $\mathrm{s}$ and one $\mathrm{f}$ electrons are each confined to their $l$ level, which is why I thought the multiplicity of microstates would be the product of the above formula for each, but I'm not sure.


texts: General rules to predict solubility in water

texts:
We were taught these rules to predict the order of solubility in general cases.

This is the theory we were taught:
Case1) When number of cations is greater than number of anions,
Solubility increases down the group
Case2) When number of anions is greater than number of cations,
Solubility decreases down the group
**
Case3**) When number of cations = number of anions,

          Case3.1) Radius of cation> radius of anion (for anions like                        >.                                Chloride, oxide, fluoride, hydroxide, sulphide)

                           Solubility increases down the group.

           Case3.2) Radius of anion> radius of cation (for anions like        >.                                   Iodide, bromide and polyatomic anions**)

                           Solubility decreases down the group(but for                              >.                                  hydroxides, solubility increases down the group)

Case4) For heavier metal compounds, we always use the concept of
polarization which in turn is directly proportional to "intensity of
color" and inversely to "solubility" .

I haven't seen these rules in any book or elsewhere so I am assuming my teacher came up with these rules on his own after analyzing solubility order in many compounds.
Here are things I don't understand-
A) Why does solubility depend on the number of cations and number of anions?
B) Ionic compounds are soluble in water. For a general compound which doesn't show hydrogen bonding, its solubility should depend upon its percentage of ionic character. Comparison of percentage ionic and covalent character can be simply done using Fajan's rule. So is comparing solubility order by comparing their percentage ionic character wrong?
C) In case3, how does the radius of cation and anion affect solubility?


texts: Does the entropy of a chemical system increase in an endothermic reaction?

texts: Since entropy increases when temperature increases, the entropy of surroundings increases during an exothermic reaction. When I apply the same logic, it seems like the entropy of a chemical system increases in an endothermic reaction. Is this true?


texts:
I'm given a question:

  Oxidation number of $\ce{O}$ in $\ce{BaO2}$ is $x$ and in $\ce{OF2}$ is $y$; then the value of $x+y$
  is what?

Now my main question is that if $\ce{F}$ has $-1$ valency in $\ce{OF2}$ then $\ce{O}$ must have valency of $+2$. But is that possible since $\ce{O}$ mainly has oxidation states of $-1$ & $-2$ or am I making any mistake?


texts: What is the chemical composition of the liquor from egg-white?

texts:
I am following traditional techniques using egg white to make a glaise for gold leaf embossing on to leather. The glaise dries on to the leather, gold leaf is laid on it, a heated diestamp is applied and the glaise acts as a very efficient and permanent glue, capturing the gold leaf and fixing it.
Having beaten the egg white ferociously and made a foam, I then leave it overnight and in the morning a clear liquor is at the bottom and can be decanted. The foam above it becomes like a spider's web and is discarded.
I am interested in the composition of the clear, thin liquor that forms overnight.
I know that the amino acids in the proteins are either hydrophilic or hydrophobic and this causes the proteins, when air is introduced by beating, to orient themselves such that the hydrophobics are in the air and the hydrophilics in the water.
But I am uncertain as to the content of the 'spider's web' and the clear, thin liquor.
I know that there is albumen present, and globulin and related molecules such as ovotransferrin, ovalbumin and ovaglobulin, see Constituent Proteins ... from Egg White, but what exactly is it that I am doing to the egg white and what are the resulting two fractions that I am getting ?


texts: Turn lead into gold via radioactive decay

texts:
I was looking at the isotope's table and noticed that one of lead's isotopes can actually turn into stable gold through the following mechanism:

$$\ce{_{82}^{197}Pb -> _{81}^{197}Tl -> _{80}^{197}Hg -> _{79}^{197}Au}$$

I know (or at least guess) that such a process must be awfully ineffective. Still, I was wondering:

How could we get a great quantity of $\ce{_{82}^{197}Pb}$?
How long would it take for it to turn into gold? Can that be accelerated?
Once most of it has been turned into gold, how can we extract the gold (there are still remaining $\ce{Pb,Tl,Hg}$ molecules)?
What would be the yield of the process? How much money would it approximately cost compared to how much we win in gold?


texts: Using RDKit to determine "nonring, nonterminal atoms"

texts:
I am a non-chemist using RDKit to determine the number of "nonring, nonterminal atoms" in a molecule.
I can't find anything in the RDKit documentation that helps with "nonterminal". Can it be used for that?
I can using RDKit's AtomRings function to identify atoms in rings, but perhaps there is a more direct way?


texts: Why does transition state loses its ability to vibrate? (Transition State Theory)

texts:
In transition state theory, (according to my textbook) it is assumed that the the transition state loses its structure, and the ability to vibrate and rotate. If the transition state cannot vibrate, then my questions are

how does the previous bonds break and the newer bonds form?
Isn't the instablity and high potential energy of transition state
due to the  extra vibration of the atoms in the molecules?

Please guide me through this.

my book states:

  "The transition state does not represent a real molecule, it is impossible to isolate a transition state. However it is assumed to possess properties common to real molecule, such as molecular weight, intermediate distances, a definite enthalpy, definite composition but loses its structure, and the ability to rotate and vibrate. The transition state may either return to the initial reactant or it proceeds to form products."


texts: Why does Boron only need 6 valence electrons unlike the standard 8?

texts: So I was a bit confused. Hydrogen and Boron seem to be the only outliers to the octet rule. Hydrogen makes sense because it has only one shell and 2 electrons complete its shell. Boron's configuration, however, is $1s^2 2s^2 2p^1$. Having 6 valence electrons would mean having a configuration of $1s^2 2s^2 2p^4$ which doesn't seem as stable as $1s^2 2s^2 2p^6$ or even as stable as $1s^2 2s^2 2p^3$ since one would think that there is repulsion going on between electrons in the first orbital of p in $1s^2 2s^2 2p^4$. Thanks in advance!


texts: Endothermic reaction absorbs heat from environment

texts:
I read on my school book about chemistry the reaction:

$$\ce{H2O + NH4Cl}$$

with $T(\ce{H2O}) = \pu{25 °C}.$

The temperature of the final solution is $\pu{20 °C}$.
I know that it is an endothermic reaction, and the initial solution absorbs temperature from the environment.

I don't understand why the temperature of the final solution is lower than the initial solution, I think it should not be lower because  all the heat that it needs comes from the environment.


texts: Fehling's Test meaning for partial formation of a precipitate?

texts: Whilst doing tests on two unknown solutions, I used Fehling's test. The solutions could be a mixture of compounds or just one compound dissolved in water/ another solvent - I don't know. Upon adding Fehling's solution both solutions (which were originally colourless) turned a blue colour. I then heated the solutions very gently for about 5 minutes and after this time one had completely formed a red precipitate, whereas the other still had the blue solution left in it (while forming some red precipitate). After waiting for about 20 minutes both solutions had completely formed a brick red precipitate and were the same. I assume this is to do with rate of the oxidation reaction occurring. Is there any explanation as to the rate of reaction in each solution or an explanation which is not to do with rate at all perhaps?


texts: Calcium dynamics and its relationship with nitric oxide

texts: I know that in synaptic transmission nitric oxide release leads to a reduction of calcium inflow. But how does this phenomenon happen quantitatively (for example: I suppose that when the nitric oxide concentration increases, the time derivative of calcium concentration becomes negative and viceversa)? Does a numerical relationship between nitric oxide and calcium concentrations exist, in this sense?


texts: Product of the addition of 1 eq. bromine to 1-methylcyclohexa-1,4-diene

texts:
When we add one equivalent of $\ce{Br2}$ then which double bond will get brominated?

The double bond in the molecule with methyl group will be more stable as it will have more hyper conjugating structures. Thus the other double bond should get brominated.
But my textbook says the double bond with methyl group will get brominated. Can someone explain why?


texts:
I do some experiments with liquid mercury and I use a special bottle that was 3d printed (ABS plastic). To prevent leaking of mercury I use 502 glue layered around the bottle.

I want to know, if it is safe to store mercury in this bottle?

Does mercury interact with something in 502 glue?

502 glue: Methylene Chloride , Ethyl acetate, Toluene, Cyclohexane

I am not a professional at chemistry.


texts: Is brass combustible in high pressure oxygen environment?

texts: Some metals are particularly ignitable in high pressure oxygen environments, like stainless steel and aluminum. Copper and nickel, on the other hand will self-extinguish when ignited. Does anyone know about brass?


texts: stability of a negative charge in halogens and that of orbitals

texts:
when we talk about stability of halogen anions we say,
$\ce{I-} \gt \ce{Br-} \gt \ce{Cl-} \gt \ce{F-}$, and the reason is that "the negative charge (the electrons) have more space to move about in the larger halogen". But when we talk about stability of a negative charge on an orbital, why do we say that the negative charge on the $sp$ hybridized orbital (which is the smaller one) is more stable than $sp^2$ and then $sp^3$ as the least stable where as the  $sp^3$ orbital is the biggest orbital among all of the three and can allow the electrons to spread out more.


texts: Standard state conditions in thermodynamics

texts:
Standard state conditions for standard Gibbs energy change stipulate (among other conditions) that partial pressure of each gas = 1 bar.
e.g. 2A + 3B = 4C + 5D (all gases)
Then for standard Gibbs energy change calculations partial pressure of A or B or C or D is same = 1 bar.
What I want to know is that if we are calculating standard enthalpy change for the above reaction are the partial pressures still 1 bar for every gas? Or is the external pressure = constant = 1 bar ? Because if the external pressure = 1 bar then partial pressure for every gas can't be 1 bar [ if 2 moles of A are at 1 bar then 3 moles of B will have a higher pressure, if they are all present in the same closed container]


texts: Cycloaddition of Silyl Dienol Ethers with Sodium Bromodifluoroacetate: What's the scope?

texts:
I have recently came across this article "Copper(I)-Catalyzed [4 + 1] Cycloaddition of Silyl Dienol Ethers with Sodium Bromodifluoroacetate: Access to
β,β‐Difluorocyclopentanone Derivatives". (Org. Lett. 2016, 18 (18), 4502–4505)

Can anyone explain what is the use of these β,β‐Difluorocyclopentanone Derivatives or where can I find more information about this cycloaddition procedure.
Thanks in advance!


texts: Does dichlorobis(triphenylphosphine)nickel(II) have a d⁰ electron count?

texts: I am currently in dilemma because I'm trying to construct an octahedral splitting diagram for the $\ce{NiCl2(PPh3)2}$ complex. If the complex is $\mathrm{d^0}$ system, how would I determine whether the isomer is paramagnetic or diamagnetic?


texts:
Question:

  A reaction involving two different reactants can never be a

  unimolecular reaction
  bimolecular reaction
  second order reaction
  first order reaction

The answer as per my book is 1. unimolecular.
But the nucleophilic substitution SN1 is unimolecular but it involves two different reactants. Let us take an example,
$$\ce{(CH3)3C-Cl + Br- -> (CH3)3C-Br + Cl-}$$ This follows SN1 mechanism. Yet, it involves two different reactants even though the R.D.S depends only on the formation of carbocation and the rate law expression being
$$\text{rate} = k[\ce{(CH3)3C-Cl}]$$ where $k$ is the rate constant.
So, is the answer that unimolecular reactions can never involve two different reactants wrong? Or am I missing something trivial?
Also it would be great if other options are discussed.


texts:
I want to understand the mechanism of desilylation of trimethylsilyl under fluoride conditions in methanol, because I can't find any useful info that makes me understand the mechanism that takes place.

I did find this:

But my case is a little bit different because a terminal alkyne is bonded to the silyl group instead of oxygen:

Why would that bond be broken and not any other carbon-hydrogen bond?

Thanks in advance!


texts: Decomposition of CaCO3 in a sealed vessel

texts:
For the equilibrium

$$\ce{CaCO3(s) <=> CaO(s) + CO2(g)}$$

$\Delta H^\ominus = 178\ \mathrm{kJ\ mol^{-1}}$ and $\Delta S^\ominus = 160\ \mathrm{J\ mol^{-1}}$.

I'm asked to suppose that $1\ \mathrm{mol}$ of $\ce{CaCO3}$ and $1\ \mathrm{mol}$ of $\ce{CO2}$ are heated reversibly in a closed vessel under a pressure of one bar.

How much $\ce{CaCO3}$ is present in the container when the temperature reaches $1100\ \mathrm K$?

I know that at this temperature $\Delta G^\ominus = 2\ \mathrm{kJ\ mol^{-1}}$ and $K_p = 0.80$. I'm thinking that since the equilibrium constant $K = p(\ce{CO2})/p^\ominus$ is less than $1$, then the $\ce{CO2}$ would combine with any $\ce{CaO}$ around to make $\ce{CaCO3}$, but since there isn't any the composition must remain unchanged at $1\ \mathrm{mol}$ $\ce{CaCO3}$ and $1\ \mathrm{mol}$ $\ce{CO2}$. Is this right?

Now suppose the temperature reaches $1120\ \mathrm K$, at which $K_p = 1.14$. Some of the $\ce{CaCO3}$ will start to decompose, right? Suppose $n$ mol do, so that I have $1-n$ mol of CaCO3, $n$ mol of $\ce{CaO}$ and $1+n$ mol of $\ce{CO2}$.

How do I find $n$?


texts: Copper sulphate, Benedict's Reagent and albumin

texts: When my student's add Benedict's Reagent to albumin and heat it, the solution turns purple (as if testing for proteins).  Is it possible that the copper sulphate in the Benedict's is reacting with the protein in the albumin?


texts:
In transition elements shielding effect is observed . Due to this zinc shows abnormality in atomic size.
But at the same time we also say that gallium has same similar size as  aluminium due to poor shielding effect of d electrons . Why is it that d electrons have good shielding effect in case of zinc but poor shielding effect in case of gallium?


texts: Do molecules with a hexagonal planar geometry exist?

texts:
I recently read an article on Wikipedia about pentagonal planar geometry.

There are only two molecules with this kind of geometry $\ce{XeF5-}$ and  $\ce{IF5^2-}$  and it has two electron pairs at the axial positions.

As soon as I looked at this, I thought that hexagonal molecular geometry can also exist much the same way i.e. 6 substituents bonded to the central atom and two lone pairs at the axial positions opposite to each other.

On the page, its given that arrangement of 6 atoms in a plane is found in higher coordination states but that does not help either as they have not given any examples of that.

Do hexagonal planar molecules exist, and if they do, what are they?


texts: Additives to allow wax to melt in the microwave?

texts:
I'm working with microcrystalline wax that I would like to be able to microwave to heat up. I've found that wax doesn't seem to microwave, with the most common answer I've come across for why being that it doesn't contain any water.

Adding water doesn't seem like a valid solution in this instance, since even if I could add it to a wax mixture, it would eventually dry out anyway. Therefore, I'm looking for an additive that, once mixed in with the melted wax, will allow me to microwave it after that point. The mix ratio isn't all that important as long as it's kept below 30 percent or so, although this would depend on the additive.

In searching for a potential solution, I came across a concept called the "dielectric constant". Unless I'm misunderstanding, the higher this number the greater the capacity for heating in a microwave. Looking up numbers, this seems to make sense as the DK of paraffin (the closest material I could find to microcrystalline) is around 2, whereas water is around 80.

A potential material I found was titanium dioxide. I'm getting different numbers, but it seems to have a DK somewhere in the 100-300 range. Before going out and buying some, is it feasible that I could use this as a filler for my wax that would allow it to be microwaved?

If not, or if I'm on a completely wrong track with the dielectric constant concept, are there are other suggestions on how I could solve this problem?


texts: If a good choice of a unit cell should be the one of most symmetry ,then why keep body centered tetragonal if face centered cubic exists?

texts:
For any lattice a good choice of a unit cell is the one that is the most symmetric.
Now if every lattice made by a body centered tetragonal unit cell can be made by a face centered cubic unit cell ,which is more symmetric ,then why keep the body centered tetragonal unit cell as a class of Bravais lattice ?


texts: Cooking with vinegar and lemon juice (Carpaccio)

texts: I know the Maillard reaction to cook at 140–160 °C. I know the low temperature cooking reaction to cook at 70 °C. But which is the reaction that allow us cooking meat or fish with vinegar or lemon juice?


texts: How to take a sample of a hot salt solution without it precipitating in the cooler glassware due to the difference in solubilities at different temps?

texts:
I'm doing an investigation to see the effect of temperature on the solubility product of strontium hydroxide.

I made a supersaturated solution left in the oven overnight at 85°C for equilibrium to be reached. Now, I want to titrate it against $\ce{HCl}$, but when I try to pipette a 25 mL sample of the (very hot) solution, it quickly crystallises in the pipette due to the large difference in solubility at 85°C compared to room temperature.

(NOTE: doing at lower temperature is not an option.... )

One idea I can think of is to keep the glassware in the oven overnight with the solution so that it's more or less at the same temperature. (Then, I'd have to handle with a cloth, of course). However, I do not have access to an oven that is big enough to fit a pipette.

Hence, the only option I have is to use a cylinder rather than a pipette, but that would increase my uncertainties by A LOT.

Can anyone think of anything else that I could do?
Would really appreciate any help.


texts:
Steric hindrance is important for understanding regio-selectivity and stable conformation of molecules. I know the general definition, but can somebody explain to me in detail how does phenomenon of steric hindrance come about?

Like, to give a simple, hypothetical example, $\ce{CH4}$ is said to have no steric hindrance. But why does attacking molecule have no trouble squeezing past $\ce{H}$ atoms and attack center carbon atom. I know hydrogen atom is said to be small, but seriously how small is it?

I am asking this because when examples go beyond $\ce{H}$ atom and alkyl atoms I can't judge whether steric hindrance is present or not and thus what products are formed. Like in $\ce{(CH3)3CHOH^+}$, is there steric hindrance. It is a primary carbon cation but instead of two hydrogen then is $\ce{OH^-}$ group?


texts:
Heat of formation of aqueous $\ce{H+}$ is taken to be zero, by convention. Heat of formation is energy released or absorbed when 1 mole of a compound is formed from its elements in their standard states.
$$\ce{1/2 H2(g) -> H(g) -> H+(g) -> H+(aq)}$$
Since heat of formation of $\ce{H+(aq)}$ is assigned to be zero, this would imply that this reaction has $ΔH = 0$. Wouldn't this imply that:
$$\text{Enthalpy of atomization} + \text{Ionization energy} + \text{Heat of hydration} = 0~?$$
However, this doesn't seem to be the case:
$$435 + 1312 - 1091 = \pu{656 kJ/mol}$$
Where am I going wrong here?


texts: How are the two formulas for enantiomeric excess/optical purity equal?

texts:
I’ve been given two formulas to use for enantiomeric excess or optical purity:
$$\frac{\text{observed rotation}}{\text{specific rotation of pure enantiomer}}\:\:\:\:\:\times\:100\%\tag{1}$$
$$\frac{|d-l|}{d+l}\:\times\:100\%\tag{2}$$
However, I cannot figure out how they are equal to each other. You could rewrite equation (1) as
$$\frac{\alpha_d-\alpha_l}{[\alpha]}\:\times\:100\%$$
and because $\alpha=[\alpha]cL$,
$$(c_dL-c_lL)\:\times\:100\%$$
However, that’s as far as I got. I can’t see how you would eliminate L, and even doing so would not bring it to resemble the second equation. I would appreciate it if someone could offer a mathematical proof or—if this isn’t even a matter of mathematics at all but rather a conceptual misunderstanding—clarify things for me.

EDIT

$d$ is the mass of the dextrorotary enantiomer and $l$ is the mass of the levorotary enantiomer. $c$ refers to concentration, $L$ the pathlength travelled by light, [$\alpha$] specific rotatio, and $\alpha$ (without the brackets) means observed rotation.


texts:
What is the major product when the following compound undergoes Étard reaction?

Is it acetophenone or a terminal aldehyde.
The mechanism discussed in Mechanism for an Étard reaction (chromium complex) does not give any conclusive prediction.


texts:
Would an alternating electric field cause net motion of ions in a liquid in the case of the electrodes being placed outside the liquid?

Generally speaking, what happens if you apply an external electric field to an ionic liquid, taking into account that there are no electrodes places inside the liquid itself, but are separate from the liquid container in the same manner you have a parallel plate capacitor.


texts:
This seems like a farce...

  Quantum gas goes below absolute zero
  Ultracold atoms pave way for negative-Kelvin materials.
  by Zeeya Merali, Nature News 03 January 2013, DOI: 10.1038/nature.2013.12146

I have seen several recent articles like this one  and I am extremely skeptical. Perhaps my skepticism is based upon an ignorance of physical principles, but I am less offended by apparent violations of the speed of light than by considering that temperatures below absolute zero could exist. I have studied under scientists who were using advanced techniques and vast amounts of energy to get small samples cooled down to a few nanokelvin. The physics seems to imply that if a sample were to reach zero, even the nuclear forces cohering the particles would cease. This was hypothesized in hushed tones, in awe and reverence. Now this article (which seems akin to scientific blasphemy) is causing an existential crisis. What is the deal with negative absolute temperature?


texts: First Order Degradation Constant (λ)(d^-1)

texts:
Can you please tell me the First Order Degradation Constant (λ)($d^{-1}$) for 1,3,5-Trimethylbenzene (mesitylene)?

If you don't have this value, can you please tell me which VOC in 35 Illinois Administrative Code 740. Appendix A. Table A. is "most similar" to 1,3,5-TMB that I may use its First Order Degradation Constant? Please provide an explanation. Thank you!


texts: n-Chlorobutane addition to benzene by Friedel-Crafts mechanism

texts:
I recently had an exam question, pictured below, regarding a Friedel-Crafts alkylation of benzene. The question wants to know what would form as the major product. I responded that the second option, sec-butylbenzene, would form as the major product. This response was marked incorrect. I discussed the item with the professor, who told me that the correct answer (last option) was that "more than one of these products" would form.
I located a textbook example, also pictured below, which lists the sec-butyl product as the major (49% yield), and the n-butylbenzene as the minor (29% yield). This sums to 78% of the yield. I wholly agree that more products will form, but I see no evidence to suggest that they could be considered a majority product.
I have searched Reaxys and ACS for clarifying literature, but have not found anything helpful. Is anyone aware of literature which would offer experimental data to support either position, or perhaps another way that I should be thinking about this reaction?


texts: What is the ANO-RCC basis set and how does it work?


texts: Why do SN2 reactions of alkyl halides proceed differently with KCN and AgCN?

texts: Alkyl halides react with $\ce{KCN}$ to form alkyl cyanides as the main product, whereas the use of $\ce{AgCN}$ leads to isocyanides as the chief product. Why does this happen?


texts: Why does treatment of a geminal dihalide with sodium amide lead to an alkyne and not an allene?

texts:
I've come across the following problem in Klein's Organic Chemistry, 2nd edition:

However, I'm a little bit confused about why the terminal alkyne is produced. I believe that an allene should be formed via stepwise elimination of HBr, using the strong base NaNH2. The first elimination should give the more substituted, more thermodynamically stable alkene (Zaitsev's rule):

Why does the former occur instead of the latter?


texts:
I came across this structure which has got pi bonds only in its canonical forms (which are also unstable compared to the Ist structure), is it aromatic?

Also, is it compulsory for an aromatic compound to contain a carbon ring? Can't a conjugate system without carbon be aromatic (as in this case)?


texts: Reaction between n-butylithium and either an aromatic bromide or an alkylbromide

texts: What exactly happens? Does the butylithium chain add to the carbon where the bromine is attached? or do the 2 undergo halogen metal exchange?


texts: Why is Density Functional Theory notoriously bad at describing oxygen molecules?

texts:
I read in several papers that DFT is notoriously bad at describing free oxygen molecules but in none of them an explanation or reference concerning the problem has been provided. I guess this has something to do with its triplet ground state but I haven't come across a good explanation yet. Could you help me out?

Update: If someone wants to know the papers I'm refering to, here are the links and the passages that are most relevant (both groups use gradient-corrected (GGA) density functionals, so maybe this isn't a general problem of DFT but only of GGA- or LDA-functionals):

Rossmeisl et al. have devised a method for calculating the Gibbs Free Energy of the intermediate in the oxygen evolution reaction. The intermediates are treated with DFT but in order to calculate the Free Energy of the final products, including desorbed oxygen molecules, they use tabulated values.

  The free energy change of total
  reaction: $\ce{H2O -> 1/2 O2 + H2}$ is fixed at the experimentally found value of 2.46 eV per water molecule. This is done in order to avoid calculations of $\ce{O2}$, since this molecule has a complicated electronic structure, which is not described accurately with DFT.

There are other groups studying water splitting that use the experimental value too, instead of calculating it with DFT.
The paper by Bloechl includes calculations of the binding energies of a hydrogen molecule, which are in rather good agreement with experiment (4.338 eV (DFT) vs. 4.448 eV (exp.)), and of an oxygen molecule, where the DFT value is off by 0.795 eV.

  The binding energy of an oxygen molecule is calculated to be 5.912 eV, including the zero-point vibartion energy of 0.110 eV, which is comparable to the atomization energy of 5.906 eV, obtained with the Becke-Perdew-Wang gradient-corrected density functional. At 5.116 eV, the experimental binding energy is substantially smaller (by 0.795 eV) than the theoretical prediction.


texts: Mechanism for reaction of an allene with the Grignard Reagent(RMgX)

texts:
How does the Grignard Reagent($\ce{RMgX}$) react with an allene $\ce{CH_2=C=CH_2}$ and what are the products formed?

This is exactly what I tried to do.

Any help will be appreciated.


texts: How to synthesize t-Boc protected derivative of PVA

texts:
I've been toying with different potential recipes for DIY photoresist. My current favored design is a chemically amplified resist based on PVA (poly(vinyl alcohol)). For those who are unaware, a CAR works like this: a polymer is functionalized with a protecting group, and is mixed with a photoacid generator (PAG), which as the name suggests, generates acid upon exposure to light. The acid then cleaves the protecting group (in this case, t-Boc), rendering the polymer soluble in the developer. Basically, my question is how to functionalize PVA with the t-Boc group.

References are scant, but I did find one, which is unfortunately extremely vague. It says to react fully hydrolyzed PVA with di-tert-butyl dicarbonate (boc anhydride) and sodium hydride in N-methylpyrrolidone. However, the paper itself says that this reaction is not very predictable, and the authors are (were?) looking for better options.

Not being satisfied, I decided to lookup the reaction used for functionalizing poly(hydroxystyrene), which is the polymer used in the original CAR, APEX. Unfortunately, I wasn't really able to find anything on this either, save for even more vague references.

Anyhow, I have looked up information on how amino acids are protected with t-Boc, but the problem here is that I'm not sure if that would even work on PVA.

Does anyone have any idea how I would I go about doing this? Even more preferable would be a method not involving dangerous/explosive and for that matter, expensive substances such as Sodium hydride, or dangerous solvents (although NMP is not really that bad).

I did find one option  that simply involves reacting amino acids directly with molten boc anhydride. Is it likely this procedure would work with PVA?


texts:
In my current job we use gloveboxes, but unlike most we use disposable PVC bags on the entry ports instead of fixed gloves. The bags have an O ring which is stretched onto a spigot proud of the porthole and are then clamped into place. They get disposed of and replaced after every use.

^ Like this but our glovebox is permanent ^

The problem with the PVC bags is that they are releasing hydrogen chloride. I'm in a team investigating a replacement material; however none of us are chemists or material scientists!

The material needs to be able to fit over 6” and/or 10" spigots, allow hydrogen to pass, and contain no halides.

So far we have considered using HDPE + plasticizer, and are trying to find a way to make it, although we are not sure it will work until we try it. We have also looked into using polyester, but we couldn’t find a clear and stretchy version.


texts: What kind of plastic is (really) safe to store vegetable oil?

texts:
Storing colza or olive oil in a plastic bottle might be risky since the oil can leach out phthalates and BPA (and others molecules?).

Some manufacturers sell "phthalates and BPA free bottles", but are they safe to store oil?

What kind of plastic would you use to store oil?


texts: How to use NMR readings to determine the molecular structure of a compound?

texts:
A question in my exam came as follows:

How is NMR used in the determination of structure of organic compounds?

I have studied NMR spectroscopy and I know how to determine values using an NMR spectroscope. However, none of my textbooks talk about how to actually use these readings to determine the actual molecular structure of the compound that is under study. My professor has not taught this either. I was unable to find any external sources that talk about this as well.
Could someone explain the steps on how to determine the molecular structure of a compound after knowing the spectrum?


texts: Is there anything akin to molecular chirality for crystalline?

texts: For example, in hexagonal closed-packed (HCP) structure, the atoms may be arranged in ABAB stacks or ACAC stacks. Can these two be considered enantiomers? Do they possess different solid state properties?


texts:
I have a hot and cold water dispensing machine from my water company. I use 5 gallon water jugs delivered ever 3-4 weeks. The machine has a tank in it where water is kept cold until dispensed by gravity into whatever container I choose to use.

In the bottom of the tank I found a gelatin looking liquid in the bottom.  There was also ice formed where that tank is cooled. My company says its from the hot part of the machine heating water then the cool part cooling it causing the minerals to separate and not dissolve back into the water. I have never seen gelatin minerals before but wondered it this is something I need to look into further.


texts: Transposition in vicinal diols dehydration

texts: In this reaction, I don't know how I could place a methyl in the benzyl carbon. My first idea was to treat the compound with OsO4/H2O2 to form the vicinal diol, and then dehydrate in acidic medium and heat, but in this way I assume that carbocation is formed in the most substituted carbon, so I suppose that it should form in the other carbon and transpose a methyl, then with an oxidation get the carbonyl in the desired position, but this is It contradicts my idea of the formation of carbocation in the most substituted carbon. Any other idea?


texts: Could Carbon Monoxide be reduced by oxidising a more reactive metal?

texts:
After studying displacement at school, I wondered if it is possible to reduce the toxic gas of carbon monoxide to less harmful and more useful substances, like so:
Carbon monoxide + metal -> Carbon + metal oxide
Where the metal is of course more reactive than carbon, higher in the reactivity series, and so would displace it.
Is this chemically possible, or does it require too much energy? Forgive me if I appear foolish, but I just wonder if it could actually happen.
After researching extensively online, the main things which come up in searches are reduction of carbon dioxide, rather than carbon monoxide.


texts: What happens to copper(II) hydroxide when it's heated? what's inside its decomposition?

texts:
So just wondering, copper(II) hydroxide undergoes thermal decomposition when it's heated. But isn't it a solid by itself too? Why does it turn into another solid and water all of a sudden?

Can someone please explain to me the reason behind it, thank you!!


texts: Determination of the most acidic hydrogen in an organic compound

texts:
Identify the most acidic hydrogen in the compound below:

Can someone please explain why is $\ce{H^\mathrm{a}}$ in the compound below more acidic than $\ce{H^\mathrm{b}}$?
This is what is written in the answer key although the conjugate base obtained from losing $\ce{H^\mathrm{b}}$ is stabilized by both resonance, and the inductive electron withdrawing nitro group.


texts: Why Mn atom show maximum valency of 4 with F atom?

texts:
Mn ($3d^5$, $4s^2$) can have maximum 7 unpaired electrons in excited state so it should have formed MnF7 molecule but it can form only MnF4 molecule.

Is it because:
$d_{xy}, d_{yz}, d_{zx}$ orbitals are not axially oriented and therefore not suitable for head on sigma overlap but can form pi bonds as in Mn2O7 molecule.


texts: Is there a diagram/flow chart available that shows which atoms fused together to make each of the elements?  I can find examples for some elements, but nothing which shows all the combinations of atoms which make up each of the naturally occurring elements.


texts: Activity of different positions in phenol with respect to electrophilic aromatic substitution

texts:
Which of the statements below is correct?

  a) The ortho and para positions are more active than the meta position.

or

  b) The ortho and para positions are activated while the meta position is deactivated.


texts: Variation of compressiblity factor with temperature

texts:
While I certainly understand the order of temperatures, I can't find a reason for the curves to intersect at one common point.

Why do the curves intersect at one point? or do they really intersect at a common point or is it a coincidence that they are intersecting in this diagram?


texts: Thermophysical properties of liquid Galden LS 230 between 25 °C and 230 °C

texts:
I'm looking for thermophysical properties of Galden LS 230, a liquid polymer (PFPE) produced by Solvay (https://www.solvay.com/en/markets-and-products/featured-products/Galden.html) at temperatures above 25 °C. Solvay only publishes properties at 25 °C.

I asked them for properties at higher temperatures, with no answer in three weeks. I also couldn't find other free online sources (this is a vapor phase soldering hobby project).

The properties published at 25 °C are:

boiling point: 230 °C
density: 1820 kg/m³
kinematic viscosity: 4.4 cSt = 4.4 × 10-6 m²/s
vapor pressure: 453.3 Pa
specific heat: 973 J/kg K
heat of evaporation at boiling point: 63 kJ/kg
thermal conductivity: 0.07 W/mK
coefficient of expansion: 0.0011 1/K
surface tension: 20 dyne/cm = 0.02 N/m
average molar weight: 1020 a.m.u
some others that I don't expect to need for thermodynamics: dielectric strength, dielectric constant, volume resistivity.

Vapor density

Using the ideal gas law to calculate the density of saturated vapor at 1 bar yields about 24.4 kg/m³, which is within the range I found in some other inofficial sources and also in a pretty hard to read plot in a solvay presentation.

Viscosity

the wikipedia page on the temperature dependence of liquid viscosity (https://en.wikipedia.org/wiki/Temperature_dependence_of_liquid_viscosity) lists a number of models that might also apply to Galden, but I'm not sure which ones would yield reasonable results. I'd be glad if someone could shed some light on this. The solvay FAQ (https://www.solvay.com/en/markets-and-products/featured-products/galden-pfpe-faq.html) shows a plot of viscosity vs. temperature for Galden HT 230, which has the same nominal boiling point as the "LS" grade, but has higher tolerances for the molecular weight distribution. The HT grade also starts with the same viscosity at 25 °C as the LS grade. If all else fails, I might use that value.

Specific heat

I'm not sure if it's reasonable to assume specific heat to remain close to constant. My gut feeling is "probably".

Thermal conductivity

Since Galden is a non-metal, I'd expect thermal conductivity to remain more or less constant, or to increase slightly. How large or how significant the change would be, I don't know.

Surface tension

I expect surface tension to decrease with increasing temperature, according to the Eötvös Rule (https://en.wikipedia.org/wiki/E%C3%B6tv%C3%B6s_rule), but to really calculate values I'd need information about the critical point of this polymer (if that even exists, anyway).

A bit more technical background

In vapor phase soldering, a printed circuit board with solder paste and components is immersed into high temperature vapor (such as that of Galden). To create this vapor, the liquid has to be heated and evaporated. This must be done carefully because Galden starts to decompose at 290 to 300 °C. All the properties above are required to calculate a Nusselt number for nucleate boiling, so that I can determine the actual temperature at the heating surface, which will be higher than 230 °C.


texts: what is the mass of chromium in this sample?

texts:
If the total number of atoms in a sample of potassium dichromate is $2.13\cdot10^{24}$ , then the amount of chromium in this sample is?
the answer that I've come up with is $367.64\ \mathrm g$
but in fact the solution in my book is $33.4\ \mathrm g$.


texts: How to control the potential of an electrode?

texts:
I Have been reading about redox potential and Nernst equation. However, I got the understanding that the potential for the material is fixed (excluding Temperature).
My Problem: I have two electrodes and I want to increase the potential difference between them. I do not want to replace the material of the electrodes yet. Any tips!
Also, is there a list of chemical components based on their redox potential?


texts:
I poured some water in a balloon, inflated, and tied it up.  Over a period of couple weeks, all water in the balloon is gone.  But the balloon is still at about 2/3 of original inflated size.

I thought the the air molecules are much smaller than water vapor.  Why the water is all vaporized?


texts: How does an acid prevents or discourges oxidation of iron?

texts: In the titration of $\ce{KMnO4}$ with Mohr's salt, I have learned that sulphuric acid prevents oxidation of $\ce{Fe^2+}$ to $\ce{Fe^3+}$ in the solution before the actual titration. How does the acid hampers oxidation?


texts:
I was going through the mechanism of Arndt-Eistert synthesis and got stuck in the step where silver ion is used in the rearrangement step.
If anyone can clarify the use of silver ion?
It would be a great help!


texts: Why does the excitation and emission spectrum of a fluorescent molecule have overlap?

texts:
Question is rather self-explanatory. Came up during a lecture without a concrete answer.

I understand that the differences in emission wavelengths is due to relaxation to the lowest energy level of S1, but why do fluorescent molecules necessarily overlap in their excitation and emission spectra?


texts: Is there a liquid crystal or similar material that gets cloudy when an electric field is applied, but is otherwise clear?

texts:
Is there a way to make a liquid, such as a liquid crystal material, transition from cloudy or clear and vice-versa using only electric current?

By cloudy, I mean, similar to the effect that cholesterol or 5CB exhibits, thermally.

If so, where could this be obtained, and how quickly does it switch between states?

If not, how else might such an effect be achieved using electric current? I've read about the Kerr effect, but it didn't change opacity so much as refractive index, and it also appeared to use a great deal of electricity. I'm thinking something within the single volts.


texts:
I have a pair of natural rubber dishwashing gloves. These particular gloves were brand new but sitting loose out of the package on top of the supplies under the sink.

I pulled them out today & found that one of them had developed small blisters all over the hand area, covering about four square inches. The blisters are not really concentrated in one area, although there are more along the thumb-forefinger. They are about two millimeters in diameter, some go in and some go out.

The only chemicals under the sink are vinegar, Bon Ami (mostly crushed limestone), Goo Gone (tried it; did not cause the blisters), liquid dish soap & detergent. I can't think of anything hot enough to cause that blister pattern that would have been down there. Any ideas? I'm totally stumped.


texts: How to identify the most stable Lewis adduct of boron trichloride?

texts:
Which of the following is the most stable Lewis acid–base adduct?
  (a) $\ce{H2O\bond{->}BCl3}$
  (b) $\ce{H2S\bond{->}BCl3}$
  (c) $\ce{H3N\bond{->}BCl3}$
  (d) $\ce{H3P\bond{->}BCl3}$

This is a question from KVPY 2016 examination. In my first attempt, I focused on the positive charge that is going to appear on the donating atom. So the less electronegative the donor, the better it is at donating its lone pair to the vacant orbital on boron. However, the answer key states that the answer is option (c).

I am unable to rationalize why (c) is the most stable adduct.


texts:
Can you explain to me:

What are Cis-Trans, E-Z and Syn-Anti Isomerization?
What is the difference between them?
How many functional groups is cis-trans isomerism applicable to?

I  know mostly about cis trans and E-Z but have no idea about syn- anti isomers. Correct me if needed: I think cis and trans isomers respectively occur when identical atoms or groups are on the same or opposite side of the double bond respectively. E and Z isomers are for trans and cis in complex cases where more functional groups are involved.

Also, I couldn't follow the Wikipedia Link.


texts: In electrolysis, why does each atom wait to turn into gas until they reach a particular electrode?

texts:
More specifically why don't bubbles of both oxygen and hydrogen appear everywhere?
If the electricity just breaks apart bonds wouldn’t the hydrogen and oxygen just immediately turn into gas and bubble up wherever they split apart? Why does each atom wait to turn into gas until they reach a particular electrode?


texts: What causes mercury to expand equaly unregarded what the temperature increase is?

texts: Mercury seemed to be a good liquid to use in thermometers. But why are most liquids expanding non-linearly with increase of temperature compared to other liquids?


texts: Carbon Capture Absorption with Henry's Law

texts:
Assume the Henry’s coefficient for water at $\pu{20 °C}$ is $\pu{1.6E8 Pa}.$ What is the mole fraction of $\ce{CO2}$ that will be dissolved in water assuming that it is at equilibrium with a flue gas containing $0.11$ mole fraction $\ce{CO2}$ at atmospheric pressure $(\pu{10^5 Pa})?$

My understanding is that we can use Henry's law

$$y_i\cdot p = x_i\cdot H$$

where $H$ is the given Henry's coefficient. This yields a solution for $x(\ce{CO2}) = \pu{6.89E-5}.$

  A coal plant emits $\pu{120 kg s-1}$ of $\ce{CO2}$ at a mole fraction of $0.11$ and atmospheric pressure $(\pu{10^5 Pa}).$ Assuming that the flue gas and water come fully into equilibrium during separation, what flow rate of water $[\pu{m3 s-1}]$ would be needed to capture $95\%$ of the $\ce{CO2}?$

For this part, I'm a bit confused as to where our $x(\ce{CO2})$ and the $95\%$ capture rate comes into the play. I assume after you calculate a new mole fraction, some dimensional analysis is involved to get from $\pu{kg s-1}$ to $\pu{m3 s-1}.$

Any insight to this would be appreciated.


texts: How can antibonding orbitals be more antibonding than bonding orbitals are bonding?

texts:
In molecular orbital theory, the fact that a bonding and antibonding molecular orbital pair have different energies is accompanied by the fact that the energy by which the bonding is lowered is less than the energy by which antibonding is raised, i.e. the stabilizing energy of each bonding interaction is less than the destabilising energy of antibonding. How is that possible if their sum has to equal the energies of the combining atomic orbitals and conservation of energy has to hold true?

  "Antibonding is more antibonding than bonding is bonding."

For example, the fact that $\ce{He2}$ molecule is not formed can be explained from its MO diagram, which shows that the number of electrons in antibonding and bonding molecular orbitals is the same, and since the destabilizing energy of the antibonding MO is greater than the stabilising energy of bonding MO, the molecule is not formed. This is the common line of reasoning you find at most places.