texts: Why does depurination happen at a higher pH (or under less harsh conditions) than depyrimidation?

texts:
I've always wondered why the N-glycosidic bond, which connects the adenine or guanine purine bases to their sugars, was the easiest to cleave via acid hydrolysis, or why purines have the lowest ionization potentials?  What is it about the rings / resonance / etc. of purine vs. pyrimidine bases in nucleic acid polymers that makes this so?  For example, according to (Lindahl, Nature 362, pp. 709–715 (1993), http://www.nature.com/nature/journal/v362/n6422/abs/362709a0.html), at least in the context of deoxyribonucleic acid (DNA) at pH ~ 7 (probably the rate is much slower in RNA under the same conditions due to the 2'-OH) the rate of depyrimidation is $\approx 20$ fold slower than the rate of depurination.  Note that the actual base rate of depurination is $\approx 4 \times 10^{-9} \space \mathrm s^{-1}$ at 70 °C and pH ~ 7.4 (Lindahl & Nyberg, Biochemistry 11(19), pp. 3610–3618 (1972), http://pubs.acs.org/doi/abs/10.1021/bi00769a018), implying a base rate for depyrimidation of $\approx 2^{-10} \space \mathrm s^{-1}$ under the same conditions.

If I had to guess, I'd say that the reason has to do with purine bases (or the local context of the N9-glycosidic bond on purine bases) being less electrophilic, which is why I mention generally lower ionization energies for purines vs. pyrimidines.

Quoting from: http://www.nrcresearchpress.com/doi/abs/10.1139/o74-139#.U32-3vmSyDZ

"Contrary to previous suggestions, pyrimidine as well as purine deoxynucleosides are subject to base cleavage, the relative ease of thermolysis being 2′-deoxyguanosine > 2′-deoxyadenosine > 2′-deoxycytidine > 2′-deoxyuridine > thymidine."

Note that this actually seems to match the relative (experimentally measured) ionization energies of the bases --- Guanine (7.77 eV) < Adenine (8.26 eV) < Cytosine (8.68 eV) < Thymine (8.87 eV): Orlov, V. M., Smirnov, A. N., Varshavsky, Y. M. Ionization potentials and electron-donor ability of nucleic acid babes and their analogues. Tetra Lett. 1976;17(48):4377–4378.

If my guess regarding the lower electrophilicity of purine bases is true, it's not clear to me, however, why this is the case?

Update / Thought:

If we look at the four bases (where uracil is just missing the C5 methyl group on thymine) - (http://img.sparknotes.com/figures/7/749a4182b7527e44d289a612e420f40c/dna_bases.gif) - we can notice that the N9 nitrogen connecting purines to their sugars is only ever adjacent to carbon atoms with single- or double-bonds to nitrogen.  However, the N1 nitrogen connecting pyrimidines to their sugars is adjacent to a C2 carbon double-bonded with an oxygen atom.  Given that oxygen is more electronegative than nitrogen (oxygen has an electronegativity of ~3.44 vs. nitrogen's electronegativity of ~3.04) could this be a hint as to why depyrimidation is much less common than depurination?  Are there pyrimidine base analogues with a less electronegative group attached to the C2 carbon, and do depyrimidation rates here match or exceed depurination rates?

This could, of course, be completely off.  For example, maybe N7 protonation on purines presents a route to depurination, since guanine having a greater depurination rate than adenine (or lower ionization energy than adenine) is consistent with a decrease in the N7 nitrogen's basicity.  Maybe pyrimidines are much less prone to destabilizing protonation.  Etc.

*

My objective here: I'd like to know the "most significant" factor for (and hopefully most general reason for) the greater observed rates of depurination vs. depyrimidation.  For example, perhaps the aforementioned oxygen on pyrimidines decreases depyrimidation rates by a factor of two or so (this isn't meant to be an actual guess), but what explains the $\approx 20$ fold difference noted by (Lindahl, 1993)?


texts: Mechanism for reaction of enol ether with HBr

texts:
Please refer to the image for the question. I tried two different mechanisms for the reaction (1 and 2) and ended up with two different products. Now I can't decide which of the two mechanisms would give the major product.

I think that mechanism 1 should give the major product as it involves the formation of a double bond between $\ce{C}$ and $\ce{O}$ atom which is thermodynamically favorable. Is this reasoning correct?

The answer to the question had given product of mechanism 2 as major product. But I don't know if it is really correct or not.


texts: I Would like to know if its possible to get a reaction between KOH at ~50% (w/w) and an usual PVC pipe? If yes what kind?


texts: Readings about chiral resolutions at the undergraduate level

texts:
Does anyone know of a resource which clearly explains the scientific theory and experimental methods involved in chiral resolutions?

I have access to the American Chemical Society, Tetrahedron, Royal Society of Chemistry and many other journals and books.

I am an undergraduate student doing laboratory research. I am about to separate enantiomers, which are atropisomers. I am looking for something that I can understand with my limited experience, as I have only taken two semesters of undergraduate organic chemistry. Also, maybe something brief since I will have to do the resolutions in only a few weeks, but that is less important.


texts: Is the graph that is attached (a form of the arrhenius equation) only used when the temperature is varied?

texts:
determine the approximate value of Ea with its appropriate units.

In my lab course, I am doing an experiment on the rate of reaction, but all three of my trials were using the same temperature. That would just result in a straight vertical line, correct?

EDIT: It was brought to my attention that I would have to use varying temperatures for this form of graph. I will be using a similar form of the example shown, but I'll be using log instead of ln which can be seen in problem 6. Would this result in a positive slope? Am I able to estimate the activation energy of all 3 parts or
just the activation energy overall, and how do I go about doing it?


texts:
From  Costanzo's Physiology:

Osmosis of water is not diffusion of water: Osmosis occurs because of a pressure difference, whereas diffusion occurs because of a concentration (or activity) difference of water.

Also from Costanzo, describing two solutions 1, and 2 , seprated by a semipermeable membrane, and 1 having a higher concentration of solute:

The solute in Solution 1 produces an osmotic pressure and causes, by the interaction of solutes with pores in the membrane a reduction in hydrostatic pressure of Solution 1. The resulting hydrostatic pressure difference across the membrane then causes water to flow from Solution 2 into Solution 1.

My question is:
How does the solute produce an osomtic pressure, and what type of interactions with the membrane pores causes the reduction in hydrostatic pressure that ultimately drive water movement?


texts: Arrangement of elements in the reactivity series

texts:
I have seen a variety of reactivity series of elements online and also have consulted some books regarding the arrangement of the elements. I understand that the arrangement of elements is based on degree of reactivity of elements with cold water, steam, oxygen, dilute acids etc.
Lithium is less reactive with respect to the criteria mentioned above yet it is placed on the top of more reactive elements in the reactivity series that I have observed.
What is the reason for the position of Lithium above let us say potassium and sodium which are more reactive.
Link to one of the references:
https://kaiserscience.wordpress.com/chemistry/metal-reactivity-series/


texts:
Lead (II) sulfate precipitate can be dissolved if:
a) We add an acid
b) We add EDTA
c) None of the above is true.

I think EDTA is a ligand, and if you want to dissolve the sulfate, then Pb sticks with EDTA to form a complex. And so more Pb will be formed to balance the reaction.


texts: Is the ideal gas constant not a constant if Celsius is used instead of Kelvin?

texts: For example, Charles' law does not work with Celsius. Why is this? I can only think that the gas constant is not a constant when Celsius is used rather than Kelvin.


texts:
I understand how the nitrite $\ce{NO2}$ ion can be formed and have a negative charge, but the nitrate $\ce{NO3}$ ion is confusing me. I made some simple drawings to try to explain what I don't understand:

Does the "electron from outside" that the oxygen receives, as indicated in the drawing, comes from the nitrogen atom? If so, then the N atom would be left with only 4 valence electrons instead of 5, thus being able to form another covalent bond with the extra oxygen, forming $\ce{NO3}$. Is this the correct line of thinking?


texts: Bent's rule for Sulfur trioxide and Sulfur dioxide

texts:
How is Bent's rule applied on $\ce{SO3}$ and $\ce{SO2}$?

Bond length of $\ce{SO3}$ < $\ce{SO2}$. Is this a direct consequence of applying the Bent's rule?


texts: Why should I add lithium bromide to my GPC eluent?

texts:
I'm running gel permeation chromatography (GPC) of a polar, uncharged polymer (acrylamide-based) in a polar solvent (dimethylformamide). The literature recommends adding a salt to the eluent; for my particular experiment, I'm using 0.05 M LiBr (example). Other salts are reported (Sodium Sulfate, for example) in the literature, both for this eluent/polymer mixture, and for similar polymers and eluents. Why is this done? Most papers simply report the eluent and the additives they used, with no mention of their reasoning. One paper just identifies the eluent, with no mention of any added salts; given the prevalence of the use of salts, I'm not sure if this is an oversight on their part, or if they just didn't use a salt.

If I were working with a polyelectrolyte, I would know that adding a salt would screen the charges along the polymer, reduce the $A_2$ effect, and make my data much easier to interpret. One GPC column manufacturer claims (under "What additives are important...") that dipole-dipole interactions can have a similar effect, but I'm not not sure how much to trust that claim. In addition to confirming or denying that this is the reason, I would also appreciate pointers to any relevant literature.


texts: Electrolytic cell chemical composition during/after charging?

texts:
I have a pot with some (bottled) water and added (sea) salt. It has a pencil (graphite) and tin foil (aluminum). The pencil is connected to the positive outlet of a solar panel and the tinfoil is connected to the negative outlet of the solar panel (effectively 'charging' the electrolytic cell).

To ensure I don't come to harm, I would like to know:

A) What chemical(s) gas(es) are produced at the pencil?
B) What chemical(s) gas(es) are produced at the tin foil?
C) What will the chemical composition of the water generally be (assuming I've been charging it a while)? (Acidic, toxic, etc?).


texts:
I am working on organosulfur compounds where i have S-N bonding, according to literature it might be having an ir vibration of 1100cm-1, could anyone confirm it with reference. (the complete bonding will be like S-S-N-C)
Thanks


texts: Why does (2-methoxyethyl)benzene undergo nitration at the ortho position (major product)?

texts:
This is an option in a question in which we needed to mark all the correct reactions:

According to the answer key, this is a correct option.
As an alkyl group is directly bounded to the benzene ring, I thought that the reaction will have para product as the major product.
I have a similar doubt with the nitration of toluene. I am unclear as to why ortho product is the major product.
It's be highly appreciated if anyone could please explain the reasons behind the major products of both the reactions.


texts: What is the difference between "spontaneous" and "energetically favourable"?

texts:
I read somewhere that the difference between energetically favorable reactions and spontaneous reactions is that energetically favorable reactions are ones where energy is released, i.e., $\Delta H<0$, whereas spontaneous reactions are ones where the change in Gibbs free energy is negative, i.e., $\Delta G<0$. Thus it is possible for a reaction to be energetically favorable but not spontaneous if $\Delta H$ is negative, and yet $\Delta G$ is positive because $\Delta S$ is negative and the product of it and T is large enough to compensate for $\Delta H$ as per this equation: $\Delta G = \Delta H - T(\Delta S)$.

My questions are:

1) Is this true?

2) If so, what would be an example of a reaction that is energetically favorable but not spontaneous?


texts: How to calculate the pH of a redox reaction between nickel(IV) oxide and silver?

texts:
For the following reaction:
\begin{gather}
\ce{NiO2(s) + 4 H+(aq) + 2 Ag(s) -> Ni^2+(aq) + 2H2O(l) + 2Ag+(aq)}\\
E^\circ = \pu{2.48 V}
\end{gather}
Calculate the $\mathrm{pH}$ of the solution if $E = \pu{2.23 V}$ and $[\ce{Ag+}] = [\ce{Ni^2+}] = \pu{0.023 mol/l}$.

I know that there is the Nernst equation:
$$E = E^\circ-\left(0.0592/n\right)\log Q$$
Where $E^\circ$ is the standard cell potential, $E$ is the cell potential for non-standard conditions, and at non-standard pressures or concentrations,
$$Q = \frac{[\text{products}]}{[\text{reactants}]}.$$
I know that for this problem, $n(\ce{e-}) = 4\ \mathrm{mol}$, and that
$$Q = \frac{[0.023]^3}{[\ce{H+}]^4}.$$
So:
\begin{align}
  2.23
  &= 2.48 - \frac{0.0592}{4}\log\left(\frac{0.023^3}{[\ce{H+}]^4}\right)
  \tag{1}\\
  0.25
  &= \frac{0.0592}{4}\log\left(\frac{0.023^3}{[\ce{H+}]^4}\right)
  \tag{2}\\
  1.00
  &= \frac{0.0592}{1}\log\left(\frac{0.023^3}{[\ce{H+}]^4}\right)
  \tag{3}\\
  1.00
  &= 0.0592\log\left(\frac{0.023^3}{[H^+]^4}\right)
  \tag{4}\\
  \frac{1.00}{0.0592}
  &= \log\left(\frac{0.023^3}{[\ce{H+}]^4}\right)
  \tag{5}\\
  \frac{1.00}{0.0592}
  &= \log(0.023^3)-\log\left([\ce{H+}]^4\right)
  \tag{6}\\
  \frac{1.00}{0.0592} - \log(0.023^3)
  &= -\log\left([\ce{H+}]^4\right)
  \tag{7}\\
  \frac{1.00}{0.0592} - \log(0.023^3)
  &= -4\log\left([\ce{H+}]\right)
  \tag{8}\\
  \frac{\frac{1.00}{0.0592} - \log(0.023^3)}{4}
  &= -\log\left([\ce{H+}]\right)
  \tag{9}\\
  \mathrm{pH} &= -\log\left([\ce{H+}]\right)
  \tag{10}\\
  \frac{\frac{1.00}{0.0592} - \log\left(0.023^3\right)}{4}
  &= 5.45
  \tag{11}
\end{align}
Therefore, $$\mathrm{pH} = 5.45\tag{12}.$$
Yet, the online assignment here says my answer is wrong.

It even gives me practice versions for other variations of this problem, and yet I still always get a wrong answer using the same methods.  Would someone be so kind as to point out any errors I may have made while calculating this answer?


texts: In March's Advanced Organic Chemistry (6th ed.), it's stated that the above two are atropisomers. I don't get why is it so. How is the topmost $\ce{C}$ locked in its place? Surely, there's steric hindrance due to presence of two methyls but how does that prevent rotation? It can certainly rotate with the methyls being "rigid" in their positions. Also, are they chiral? I believe they aren't because they are superimposable mirror images.


texts:
"Acetylation (adding an acetyl group) and phosphorylation (adding a phosphate group) make the histones more negatively charged because acetyl and phosphoryl groups are negative. They are "glass is half empty" molecules. By making histones more negatively charged, their grip on DNA will be much looser because DNA is also negatively charged. Similar charges (negative and negative) repel one another".

I know oxygen and carbon have different electronegativities but that generates a partial negative charge and a partial positive charge. So why do we consider the negative charge prevails over the positive charge in order to histones "repel" DNA?


texts: How to derive these general formulae for number of stereoisomers of a compound with a possible plane of symmetry?

texts:
These formulae are used if the molecule has a possible plane of symmetry. One such example would be:

Here the carbons marked with an asterisk are stereogenic centres (the asterisk is not used to mark isotopes). We can clearly see that if carbon number 2 (in the entire longest chain) and the carbon number 4 have opposite stereogenic configuration, then the molecule will be achiral because it will have a plane of symmetry. For example, (2R,3S,4S)-pentanetriol will be a meso compound with a plane of symmetry. This compound clearly satisfies the criteria we have set for the type of molecules being discussed.
Let us take another example.

Again, we see that if the molecule has the same geometrical configuration at the first and the third double bond, then the molecule has a plane of symmetry. For example, (2,7)-diphenylocta-(2Z,4E,6Z)-triene clearly has a plane of symmetry.
Our goal is to find the total number of stereoisomers such compounds can have in total. We can assume that a molecule does not have both, a double bond and a chiral centre.
In our class notes, we have written these formulae:

For geometrical isomers (i.e. in case of polyenes),

If 'n' is even (here n is the number of double bonds):$$\text{Number of stereoisomers} = 2^{n-1}+2^{n/2-1}$$
If 'n' is odd, then: $$\text{Number of stereoisomers} = 2^{n-1}+2^{(n-1)/2}$$

And for optical isomers (molecules with chiral centres):

If 'n' is even (here n is the number of chiral centres): $$\text{Number of enantiomers} = 2^{n-1}$$ $$\text{Number of meso compounds} = 2^{n/2-1}$$ $$\text{Total number of optical isomers} = 2^{n-1}+2^{n/2-1}$$
If 'n' is odd: $$\text{Number of enantiomers} = 2^{n-1}-2^{(n-1)/2}$$ $$\text{Number of meso compounds} = 2^{(n-1)/2}$$ $$\text{Total number of optical isomers} = 2^{n-1}$$

How to derive these formulae?


texts: How does DeepHF (CRISPR sgRNA design tool) compute $\Delta G_{\text{binding}}$?

texts:
I am looking at the code of DeepHF that computes $\Delta G_{\text{binding}}$, and I see that it breaks a sequence into overlapping 2-mers and compute a weighted sum according to a dictionary with 16 key values:
def dG_binding(seq):
    seq = seq.lower()
    dG = {'aa': -0.2, 'tt': -1, 'at': -0.9,
          'ta': -0.6, 'ca': -1.6, 'tg': -0.9,
          'ct': -1.8, 'ag': -0.9, 'ga': -1.5,
          'tc': -1.3, 'gt': -2.1, 'ac': -1.1,
          'cg': -1.7, 'gc': -2.7, 'gg': -2.1, 'cc': -2.9}

    seq = seq.replace( 'u', 't' )
    binding_dG = 0
    dGi = 3.1
    for i in range( 0, len( seq ) - 1 ):
        key = seq[i:i + 2]
        binding_dG += dG[key]
    binding_dG += dGi
    return binding_dG

Where do the values of each 2-mer come from? I couldn't find where these values in dG stem from.


texts: Does NaOH react with O3 to produce NaO3?

texts:
I read two reactions which I want to specify first:

$\ce{Na2O2 + O3 + H2O -> 2NaOH + 2O2}$
$\ce{2KOH +  5O3 -> 2KO3 + 5O2 + H2O}$

Does $\ce{NaOH}$ also undergo a further reaction to produce $\ce{NaO3}$ or not? Since both are alkali metals and with relatively similar sizes(?), I thought it could, but Google doesn't show me anything apart from a reaction balancer site which just shows me the reverse equilibrium of the above reaction.


texts:
Humans typically achieve combustion by starting a chemical reaction of a fuel (often a carbon $\ce{C}$ containing fluid like methane $\ce{CH4}$), which is is brought into an an oxidizer (a gas containing $\ce{O}$, like air). For example, when you turn on a lighter.

What would happen if the situation were turned around?
We have an open space entirely filled with fuel and we let in some oxygen-containing fluid. How would the combustion look?

I know the (adiabatic?) temperature maximum of a flame will be achieved at conditions which are slightly on the fat side. But I have no idea how, for example, the production of unburned $\ce{C}$'s, soot production and so on, would look.


texts:
In my advisor's Ph.D. research, she used IR spectroscopy to (help) determine the conformation of a compound of interest (its structure is known.)

In organic chemistry, I learned about using IR as a way to identify functional groups (and in conjunction with HNMR, CNMR, & mass spec, I was able to determine the structure of a compound.)

How can one determine conformation using IR? What are the limitations of this? I feel like it could get messy really quickly.


texts: What are some of the more easily manipulated residues on an enzyme?

texts:
I am trying to attach a cross-linker to an enzyme and I am looking for candidates for reaction sites. I have several amino acids that are present on the surface of the enzyme (hydrophilic) but I am hoping someone can give some tips for amino acids that are easier to attach linkers to.

I originally was planning on attaching a linker to lysine because it is among the more reactive residues but my enzyme lacks a sufficient number of lysine groups.

Could any one give me some general advice on which amino acids would be better to investigate first? I know the specific residue I choose will depend mostly on the structure of the enzyme, but if you could give me a suggestion of which amino acids are typically easier to manipulate (ie. Lysine > glycine) I would greatly appreciate it.


texts: Quantitative Transfer of Volatile Standards

texts:
(Edited w/ updates) Okay, long story short I work in a lab which has been working on cannabinoid analysis (in the licensed Canadian market) and have had a lot of issues surrounding the standards/response factors varying over time.

They are only available in pure methanol or ACN, are very expensive, and only come in $\pu{1 mL}$ quantities. I currently micropipette $\pu{150 \mu L}$ of these into a vial and then dilute, though the vapour pressure of the solvent causes it to immediately push droplets back out of the pipette tip, meaning the volume changes slightly based on the speed at which you transfer, and I think this (among other things, like slow evaporation of retained stocks in storage) is causing variation. Relative response factors between cannabinoids vary up to 30% between different preparations on different days, which is unacceptable.

So I need to both conserve the liquid I use and find a way of transferring that can reduce the effect of volatility. I proposed weighing the ampule, transferring quantitatively to volumetric flask and weighing again, then back calculating the mass amounts using density, as the concentrations come per volume. I was confused about what my manager's issue with the idea was at first but clarified and it was about potential effect of the dissolved cannabinoids on the density of the solution via partial molar volume effects on the manufacturer's end. Aka how much would this affect density and are the concentrations they gave us reliable? They're FDA exempt, meaning they're unregulated and there is no one "gold standard" preparation or test method.

I wrote a pseudo-proof for this effect being negligible (TL;DR because 2.5mg solute of any kind out of 786mg solvent would produce a variation of <0.5% in density even when wildly exaggerating the partial molar volume effects) and our chief scientific officer reviewed and signed off on it so I'm going to be doing the gravimetric transfer.

Ampoule chips were not really a concern, they very reliably break cleanly and any chips are likely too small to be seen/matter much on that same ~782mg scale during my preparation.


texts: Why doesn't beta hydride elimination happen in alkenyl/aryl halides?

texts:
Beta hydride elimination is an important reaction in organometallic chemistry:

This reaction prohibits the use of saturated alkyl halides in coupling reactions, because it can take place after oxidative insertion of the metal. Alkenyl and aryl halides don't suffer from this unwanted reaction. Why? They also contain beta hydrogens, why aren't they readily eliminated?


texts:
This is going to probably be an easy question for an organic chemist, but I am looking for the proper terminology to describe the following reaction mechanism.

In particular, what is a more precise way than "hydrogen stripping" to describe the process where a photogenerated hole on an oxygen can pick off the hydrogen and its associated electron to create a radical that reforms to make formaldehyde?

Further, would I say something like "an HCO radical attacks an adsorbed methoxy to create methyl formate" or is there a more precise way to talk about it? The proper reaction names would be ideal.  Many thanks from a physical chemist who took orgo way too long ago!

EDIT: Thanks Orthocresol for the hint about hydrogen abstraction. Upon looking into things more, hydrogen abstraction aka hydrogen atom transfer (HAT), can be viewed as a subset of proton coupled electron transfer reactions (PCET). The difference is that HAT occurs with minimal solvent reorganization and between similar donors whereas PCET is more general where there can be heat transfer (i.e. it is diabatic versus adiabatic.) So I believe that PCET may be the proper name compared to "hydrogen/proton stripping".

One last question: does anyone know what the reaction between the HCO radical and the methoxy would be called?  Thanks again!


texts: Is it feasible to make dendritic crystals at home?

texts:
I've become interested in the forms of dendritic metal crystals from an aesthetic perspective, and I'm interested in whether it is feasible (from a cost, safety, resources) perspective to create metal crystals of this sort at home?

Would the energy involved, or the cost of materials, the difficulty of controlling conditions sufficiently, or the general complexity of techniques be prohibitive to a non-expert/ someone outside an institution? Are there some metals, or metal compounds (e.g. those with lower melting points - lead?) for which this might be easier?


texts: What copper oxide is being created upon electrolysis?

texts:
Whenever using copper as anode, I end up with cyan dust that doesn't dissolve in water.

What's that (presumably) oxide? Is it poisonous? Can I dissolve it in something to perform electroplating with it?


texts:
Methanol is slightly more acidic than water. Their $\mathrm{p}K_\mathrm{a}$ values, in water, are $15.5$ and $15.7$, respectively. All other aliphatic alcohols, however, are less acidic than water.

Is the following reasoning correct? This is my best rationalization; is there anything better or anything that can be added?

In both hydroxide and methoxide, we have an $\ce{O}$ bearing negative charge. In the former, we have a hydrogen attached to the $\ce{O}$. In the latter, we have a carbon attached to the $\ce{O}$. Carbon is more electronegative than hydrogen, therefore, carbon should be able to better withdraw electron density via induction from the $\ce{O}$. This is a stabilizing interaction.

We often think of methyl groups as inductively donating, but that's molecular profiling. They can inductively donate to a carbocation, partly because a carbocation is highly electronegative, so the carbocation pulls the electrons toward itself pretty well (so there's both pushing and pulling of electrons going on). When you have a methyl group attached to an $\ce{O}$, however, the methyl group is often inductively withdrawing. NMR data supports this.

Now the question is why aren't other aliphatic alcohols more acidic than water? In longer-chain aliphatic alkoxides, you don't just have a methyl group attached to the $\ce{O}$ bearing the negative charge - you have a bunch of methyl groups strung together. These lessen the amount of inductive withdrawal that the alpha carbon can do. Each$\ce{-CH2 -}$ unit attached to the alpha $\ce{-CH2 -}$ is somewhat inductive donating to the alpha $\ce{-CH2 -}$.


texts: Let's say I am seeking to find an alloy with certain properties, is there any method or process that enables one to backtrack from desired properties to actual structure and composition of a material?


texts: What's the energy density of liquid nitrogen?

texts:
Liquid nitrogen seems to be attracting a bit of attention at the moment as a medium of energy storage, both for electricity grid applications and for transport.
For example, Highview (via the Internet Archive) are doing round-trip electricity storage via liquid nitrogen.

The Dearman Engine Company (via the Internet Archive) are developing a "liquid-air" vehicle engine.
And the UK’s Institution of Mechanical Engineers has formed a Liquid Air working group (via the Internet Archive).
What is the energy density of liquid nitrogen, per unit volume and per unit weight, assuming we’ll be bringing it up to 20 °C, 1 bar? How does this compare to the energy densities of isooctane and of Li-ion batteries?


texts: Most useful reagent for gravimetric analysis of silver

texts:
My question reads as follows:

"What's the most useful reagent for the gravimetric analysis of silver from the options below:
A. Sodium nitrate
B. Barium carbonate
C. Potassium sulphate
D. Ammonium chloride"

I can rule out A and C as they do not form a silver precipitate with a solution containing silver. However, both B and D can form a silver precipitate so I am not sure which of them would be the most useful.


texts: Determine products of redox-reaction (KMnO4) by Standard electrode potential

texts:
I want to figure out a way how to determine the products of a redox-reaction by looking at the documented Standard electrode potential (for example here). But with my "way" I have some trouble/contradictions with common redox reaction, in my case the reduction of $\ce{MnO4-}.

Here is my procedure for the reduction of $\ce{MnO4-}$:

Collect all available reactions with their Standard Potential:*
\begin{align}
\ce{MnO4- + 2H2O + 4e- &-> MnO2 + 4OH-}&
E(\text{Red})&= \pu{0.83 V}\tag{a}\label{a}\\
\ce{MnO4- + H+ + e- &-> HMnO4^-}
& E(\text{Red}) &= \pu{0.72 V}\tag{b}\label{b}\\
\ce{MnO4- + 8H+ + 5e- &-> Mn^2+}&
E(\text{Red}) &= \pu{1.23 V}\tag{c}\label{c}\\
\ce{MnO4- + 4H+ + 3e- &-> MnO2 + 2H2O}&
E(\text{Red}) &=\pu{1.6 V}\tag{d}\label{d}
\end{align}
Then figure out the reaction with the highest reduction potential, because according to $E = E(\text{Red}) - E(\text{Ox})$, $E$ is maximal with the biggest $E(\text{Red})$ and the reaction is going to happen with the highest $E$.

In my example, $\eqref{d}$ has the highest potential, so according to my theory $\ce{MnO2}$ is formed in the reduction of $\ce{MnO4-}$ (in combination with for example the oxidation of $\ce{I-}$. But in all textbooks, internet sites, the reduction $\eqref{c}$ is named - not reaction $\eqref{d}$ which I had determined.

I am aware that these potentials are pH- and concentration dependent, I fit the $E(\text{Red})$-data with the Nernst-Equation to $\mathrm{pH} = 3$. Nevertheless, $E(\text{Red})$ of $\eqref{d}$ is always higher in $E(\text{Red})$ than $\eqref{c}$. According to my calculations (graph of $\eqref{d}$) which is dependent on the $\mathrm{pH}$ is always higher than $\eqref{c}$).

I have drawn a diagram which shows the $E(\text{Red})$ potential of the two reaction $\eqref{c}$ and $\eqref{d}$ (see legend). Reaction $\eqref{d}$ has always the higher standard potential - is the better oxidation reaction. Why does nevertheless reaction $\eqref{d}$ happen in acid solutions?

Functions calculated with Nernst-Equation:
\begin{align}
E(\text{pH}) &= 1.507 - \frac{0.059}{5} \cdot 8 \text{pH}\tag{c'}\\
E(\text{pH}) &= 1.7 - \frac{0.059}{3} \cdot 4 \text{pH}\tag{d'}
\end{align}
(other concentrations are assumed as equal)


texts: Regarding Analysis for CO2 Absorption in NaOH

texts:
Background

Lab experiment, packed glass column (random packing of metal/ceramic material), countercurrent gas absorption, flowrates measured using rotameters, $rt \approx 27^\circ C$.

2 N NaOH flows downwards at 10-30 mL/s; Air + $\ce{CO2}$ (~10% $\ce{CO2}$ (v/v)) flows upwards at total rate of ~350-500 mL/s.

Samples were collected as (I) 10 mL + (II) 10 mL from the bottom of the column. An excess of $\ce{BaCl2}$ was added to (II). Both are titrated against 0.5 N HCl with phenolphthalein ($\ce{HPh}$) as indicator.

Expected Reactions

$$\ce{2NaOH + CO2 \to Na2CO3}$$
$$\ce{Na2CO3 + BaCl2 \to BaCO3 + 2NaCl}$$

Colour changes:

$$\ce{HPh + HO- \to Ph- + H2O}$$

$\ce{HPh}$ is colourless and $\ce{Ph-}$ is pink

The Problem

The first few readings were as expected and no irregularities were observed. The volumes of HCl added were $<$ 15 mL.

Later

On adding indicator and waiting for some time, the colour disappeared
(pink $\to$ colourless) for both (I) and (II). Shaking sped
up the colour change process.
On adding indicator and starting titration immediately, the colour
lightened (did not fade away completely) for a considerable volume of
HCl added, then darkened considerably, and after a few more drops,
suddenly became colourless (white in case of (II)). The volume of HCl added was $>$ 40 mL. Such a great change is not expected.

One Possibility:

$\ce{CO2}$ from the atmosphere reacts with the sample to increase the acidic nature of the solution and causes the disappearance of colour.
This would explain speeding up of colour change by shaking.

But, is the rate of absorption of CO2 into a still sample of $\ce{NaOH + Na2CO3}$ this fast?

Other possibilities

Formation of buffer: $\ce{Na+}$, $\ce{CO3^{2-}}$, $\ce{HO-}$ ions are present in (I). (II) additionally contains $\ce{Ba^{2+}}$, $\ce{Cl-}$. The tap water used might be a source of $\ce{Cl-}$ as well. $\ce{HCO3-}$ formation during titration (?)
The packing material might have reacted into the system somehow. This seems unlikely, and the packings did not show signs of fouling.
The chemicals used contain impurities causing these weird effects, in which case, which type of impurites could cause this?

Note: Do comment if you more information is needed.


texts: What is the parent chain in a hydrocarbon with two different rings?

texts:
There is cyclopentyl attached to one terminal carbon atom and cyclohexyl attached to the other terminal carbon atom and there are three carbon atoms linking them. Since the cyclohexyl ring has the greatest number of carbon atoms, it should be the parent chain. So the name should be 3-cyclopentylpropyl cyclohexane.
But my book says that the middle propyl chain should be the parent chain, the cyclohexyl and cyclopentyl groups should be the substituents, and the correct answer is 1-cyclohexyl-3-cyclopently propane.
What is the correct name. And if my book is correct, why is it so?


texts: Galvanic cell using NaCl, Cu and Zn, why does it work?

texts:
Got a paper due tomorrow in chemistry, and my friends and I are totally stuck on this:
Basically we mixed some regular salt (NaCl) into a glass of water and stuck a zinc nail and a copper nail into the solution. We connected the nails and measured a voltage of .6V. Why does this happen?

I understand galvanic cells of other types and electrolysis to a pretty OK extent, but I can't for the life of me understand what's happening at a chemical level in this reaction. I also need chemical formulas and the likes. Thanks in advance!


texts:
What is the pH of a solution prepared by mixing 25.00 mL of 0.10 M methylamine, $\ce{CH3NH2}$,
with 25.00 mL of 0.10 M methylammonium chloride, $\ce{CH3NH3Cl}$? Assume that the volume of
the solutions are additive and that Kb = 3.70 × 10-4 for methylamine.

1) First, I multiplied 0.025 L with 0.10 M and received 0.0025 moles. I then divided 0.0025 moles with 0.050 L (The total volume of the solution) and received 0.05 M, the molar concentration of the methylamine and its conjugate acid in this mixture.

2) I then created an ICE Chart (my reactant was the methylamine so that I would not need to find the Ka) and I solved for "x" (which would give me the concentration of $\ce{OH}$ ions at equilibrium). First, I solved for "x" but I assumed that is was insignificant. In the end I received 10.57 as the pH, which was the wrong answer. Then when I solved for "x" using the quadratic formula (assuming that "x" was significant), I got 0.0003646 as my "x".

3) When I took the negative log of 0.0003646, I got a pOH of 3.46. I subtracted this number by 14, and I still received a pH of 10.57

4) I even attempted to use the Henderson Hasselbalch equation and still received 10.57 because the ratio of the base and acid is 1, meaning that the log is 0.

I don't understand what I am doing incorrect. The answer is supposed to be 10.87, can someone please assist me?


texts: Use of cryolite and fluorspar in electrolytic reduction of pure alumina by Hall-Héroult process

texts:
Cryolite $\ce{(Na3AlF6)}$ and fluorspar $\ce{(CaF2)}$ are added to alumina to lower the temperature of the mixture from $\pu{2000 °C}$ to about $\pu{900 °C}$ and also to increase the conductance.

But my question is about the specific effect these compounds are producing. I mean, out of the two mentioned effects, which compound is doing what?


texts: Appropriate ways to remove aluminum from the surface of glass?

texts:
I'm looking for a way to treat the surface of borosilicate glassware such that it won't contaminate solutions of puriss reagents in conditions that pure $\ce{SiO2}$ wouldn't, yet keep the bulk physical properties (and low cost) of standard borosilicate glassware.
What are appropriate ways (i.e. without etching or contaminating the glassware) to remove aluminum from the surface of borosilicate glassware to avoid it contaminating solutions?
One (inappropriate way) would be to use an $\ce{NaOH}$ solution I guess, but that would etch the glass to some extent, and thus expose more impurities in the glass.


texts: Sulphuric Acid in Esterification Reaction

texts:
Why is it that adding the sulphuric acid slowly to a solution of alcohol and carboxylic acid (making an ester) will increase the yield of the product? It seems that not only does the rate at which it is dispensed affects the yield of ester, but really does change the colour of the solution when heated. For example, my team used it slowly and the colour was a more faint peach colour whilst everyone else, who added it quickly, produced pure black solutions!

What is happening? Why does adding the acid slowly increase yield and purity of the ester?


texts:
In a nucleophilic substitution reaction , which one of the following undergoes complete inversion of configuration ?
(A) $\ce{C_6H_5CCH_3C_6H_5Br}$
(B) $\ce{C_6H_5CHCH_3Br}$
(C) $\ce{C_6H_5CHC_6H_5Br}$
(D) $\ce{C_6H_5CH_2Br}$

Clearly, the question was asking which of the following compounds underwent $\mathrm{S_N2}$ most easily, i.e the case in which the nucleophilic approach was least sterically hindered.
I eliminated (A) and (C) immediately. I then went with option (B). We had pushed the phenyl group far away from the carbon to which the bromine was attached. It would thus not sterically hinder the nucleophilic.
However, the correct answer was (D) . The explanation: The PhEt group is bulkier than the PhMe group, and hence causes more steric interference.
So , what is the fallacy in my argument? Does pushing bulky groups away  have any effect on steric interference? If so, then how far away should we push them? If not, then why not? I guess my key doubt is, under what circumstances would approach of the nucleophile be sterically compromised?


texts: Titration of H2SO4 w NaOH: Solving for the molarity of H2SO4?

texts:
I am given $\ce{H2SO4}$ in a reaction vessel of about $50~\mathrm{mL}$. I need to solve for the molarity of $\ce{H2SO4}$. A $10~\mathrm{mL}$ sample of $\ce{H2SO4}$ is removed and then titrated with $33.26~\mathrm{mL}$ of standard $0.2643\ \mathrm{M}\ \ce{NaOH}$ solution to reach the endpoint. How do I solve for titration of the $50~\mathrm{mL}$ sample?

Obviously I can use the formula:
$$M_i \times V_i = M_f \times V_f$$

Which brings me to

$$M_i \times 10~\mathrm{mL} = 0.2643~\mathrm{M} \times 33.26~\mathrm{mL}$$

Thus:

$$M_i = (0.2643~\mathrm{M} \times 33.26~\mathrm{ml}) / (10~\mathrm{mL})$$

This will find the molarity of the $10~\mathrm{mL}$ sample of $\ce{H2SO4}$.

Now, how do I find the molarity of the $50~\mathrm{mL}$ sample of $\ce{H2SO4}$ from this? Would I just do five times the $10~\mathrm{mL}$ sample's molarity?


texts: How do amines react with flue gases to absorb CO₂?

texts:
I'm reading this article about carbon capture from the combustion of fossil fuels.  In this article, it says that amines are used as a chemical absorbent to capture the $\ce{CO2}$ from the exhaust of the combustion.

In particular, I have read that N-Methyl diethanolamine (MDEA) is used (a  reference  lists the formula as $\ce{CH3N (C2H4OH)2}$).  I am curious if anyone can explain what happens during the reaction with $\ce{CO2}$ and how it absorbs the $\ce{CO2}$ from the flue gas.


texts: Rutherford projected $\alpha$-rays onto the gold foil. $\alpha$-rays are the same as a $\ce{He^2+}$ nucleus and they can ionize atoms. Therefore, why are gold atoms not ionized when the $\alpha$-rays collide with them?


texts: Mechanism for Amino-Imidazole Ring Fission

texts:
A reaction I've tried several times in the past is the hydrogenation of nitroimidazole derivative shown below. The amino product is extremely unstable and rapidly decomposes.

This instability is noted in may pieces of literature and the explanation tends to only go far as saying 'ring fission' occurs.

Question: What is the mechanism of this ring fission? To be clear, I am not interested in getting this reaction to work.... It is no longer a target of mine.

Perhaps the entire mechanism is not determinable, but I presume the amine of one molecule attacks another molecule's imidazole ring? Where would this be? How is fission occuring?

EDIT: Possibly something to do with the apparently favoured tautomerism between these two forms:

http://imgur.com/tZMLWkG


texts: Mass number of isotopes of copernicium denoted with 'm'

texts:
On this website:

http://en.wikipedia.org/wiki/Isotopes_of_copernicium

there is a sentence "This isomer is unconfirmed" as a footnote explaining two isotopes.
What do they mean by 'isomer' in this context?

Is it possible that an element may have different spatial distribution of neutrons and protons that could have an impact on its stability?


texts: Why do Ketones Have Lower Wavenumbers than Esters?

texts: The average wavenumber for a ketone is about $\pu{1720 cm-1}$ and the average wavenumber for an ester is about $\pu{1740 cm-1}$. This, however, does not make sense, as the carbonyl group of an ester should have a greater single bond character than the ketone due to resonance from the adjacent oxygen atom. This greater single bond character should thus result in a lower wavenumber for the ester, but it does not. Is there an explanation for this?


texts: How to convert 1,4 pentadiene to 1,3 pentadiene?

texts: Are there any 'conjugating agents' to accomplish the above transformation? If not, then how to proceed?


texts: Are pKa values of acid and conjugate base the same?

texts:
When you look at $\mathrm{p}K_\mathrm{a}$ table, you can read $\mathrm{p}K_\mathrm{a}$ values of acids. Do conjugate bases also have $\mathrm{p}K_\mathrm{a}$ values?

If both can have $\mathrm{p}K_\mathrm{a}$ values, why $\mathrm{p}K_\mathrm{a}$ value of conjugated bases are same as acids?
Can acid have only $\mathrm{p}K_\mathrm{a}$ values, not $\mathrm{p}K_\mathrm{b}$ values?


texts: How far has "self-organizing chemistry" gone?

texts:
This is my first question here so, please, bear with me if I go out of the style or the scope of the SE section. I think I am quite new here, so I am prone to make mistakes.

I am a molecular biologist (not a chemist, that's why I really don't know where to look for references) who wants to know more about the field of very complex chemistry-I mean the possible real experimental designs producing an increase in the number, size and network topology (as a measure of organization) of the chemical system in question. My primarily research interests have been (and still are) in the fields of theoretical, system and synthetic biology with implications for the origins of life so I could say I'm pretty aware of all the progress going on with our attempts of replicating the processes occurring in the living cells and to synthesize "artificial living organisms" related to biology. But what I'm not very aware of (because I'm not a chemist and don't know all the possible places I could look for) are other chemical reaction systems which could possibly lead to complex self-organizing behaviour. By these words I mean reactions able to produce molecules of increased dimensions (both in size and molecular weight), increased number of different reaction products (e.g. reactions generating diversity) and reaction networks able to produce increased organization between the reactions participating in them (e.g. reactions the products of which can interact with each other and form new reaction networks among themselves and even their reaction products can repeat the process generating an increase in the relationships among the reactions of the network).

I am aware of complex self-catalyzing reactions like the Belousov-Zhabotinski's reaction which are far from equilibrium but my point here isn't "only" to generate a system out of equilibrium but to understand what chemicals ("real-world" chemicals we know exist, not some hypothetical compounds we design for our needs in computer database) could potentially form a network of self-organizing reactions which can replicate and enlarge itself if given enough "raw materials". I'm not talking here about replicating biological molecules, In fact the point of my question is can such "self-organizing" networks be created with chemicals that have nothing to od with biomolecules? Can we (even in theory) use some other class (or classes) of organic molecules that could form complex interactions among themselves able to produce a network able to replicate (and even diversify) itself given enough "raw materials", e.g. substrates? Have any such experiments been done (or at least proposed) for any class of molecules different than the biomolecules we know today?

In short, can we use any class (or classes) of organic molecules to design "artificial biochemistry" and has anybody in the chemical literature explored (or even only proposed) such options? Is there any papers (in journals specialized in only in chemistry) exploring (or even only just mentioning) the idea for any particular chemicals (or interactions among classes of chemicals) you are aware of? Has such research ever been done and if so which chemicals it explored? To be as concise as possible has any chemist in any journal ever tried to propose the idea of building an "artificial biochemistry"  of any kind?

Thank you very much.


texts: Where do the rate laws for the Chlorine Dioxide-Iodine-Malonic Acid reaction come from?

texts:
After reading a section on this particular oscillatory reaction, something started bugging me about it.

However, let me lay out the basis of my question.  From what I've researched, Lengyel and Epstein proposed a model that captures the overall behavior of the system. There are a few different versions of the model in regard to the dimensions, but this seems to be the most popular:

$\ce{MA+I_2 \rightarrow IMA + I^- + H^+;\hspace{1mm} \frac{d[I_2]}{dt} = -\frac{k_{1a}[MA][I_2]}{k_{1b}+[I_2]}}$

$\ce{ClO_2 + I^2 \rightarrow ClO_2^+ + \frac{1}{2}I_2; \hspace{1mm}\frac{d[CLO_2]}{dt} = -k_2[CLO_2][I^-]}$

$\ce{ClO_2^- + 4I^- + 4H^+ \rightarrow Cl^- + 2I_2 + 2H_2O}$

$\ce{\frac{d[CLO_2^-]}{dt} = -k_{3a}[ClO_2^-][I^-][H^+]-k_{3b}[CLO_2^-][I_2]\frac{[I^-]}{u+[I^-]^2}}$

Personally, I am much more familiar with the mathematics than the chemistry.  First, are these rate laws empirical or were they derived from physical laws? Pardon me if this is a naive question, but I am not as familiar with chemistry than the other hard sciences. In basic cases, rate laws are a straight multiplication of the concentrations of the present species. However, that neglects situations involving, for example, autocatalycity.  My suspicion is that it is a mixture of processes that I'm not familiar with and simple observation.

Obviously, these reactions don't violate the laws of thermodynamics. My assumption is that the overall free energy of the system continues to decline - meaning that the system eventually reaches equilibrium.  Unfortunately, I've been at a loss to find good sources on oscillatory chemical reactions.


texts: HPLC Lab Report: Why is weight/purity % sometimes over 100%?

texts: I help with the supply chain of a small supplement company, sometimes the HPLC lab reports we get back have a weight % over 100%. What does this mean, how does this kind of thing happen? Obviously the sample can't be over 100% pure.


texts: What would be the mechanism of the given reaction?

texts:
Problem:

  $\ce{A}$ can be?

  concentrated sulphuric acid
  alcoholic potassium hydroxide
  triethylamine
  potassium tert-butoxide

My comments:

Option (A): Conc. $\ce{H2SO4}$, is an acid, it gives $\ce{H+}$ ions which must act like electrophile and add to the double bond, which must produce a carbocation and then, $\ce{HSO4^-}$ ion must act like a nucleophile and form a bond with the carbocation. Hence, the reaction must be addition of $\ce{H+}$ and $\ce{HSO4^-}$

Options (B),(C),(D): are bases, with basicity order: (D) > (B) > (C). But what would they do to an alkene?

Answer given in the book is A. How is this so?


texts:
Question: Why is ionic lattice energy inversely proportional to the radius of the atom?

Most heterogeneous covalent molecules are polar to some extent. The degree of polarity, or the dipole moment, depends on the difference in electronegativity difference between the two atoms. The larger the dipole moment, the higher the ionic character.

What I know: Electronegativity decreases as you go downward in a group, however, the size increases, usually, as you go downwards in a group. Thus, ionic character will increase upon going downward, but the ionic lattice energy will decrease? This seems contradictory. Is this true? And if it is, why is it so?


texts: Ozone layer: why shouldn’t there be holes at the poles?

texts:
Just read "What property allows ozone to absorb uv light" together with excellent answers.
The driver here, i.e. the source of both the short and long wave UV, is of course sunlight. This is notably absent for six months of the year at the poles, so can anyone explain why one would "not" expect holes in the layer there?

Also, is it true that there have never been measurements of the layer that did "not" reveal holes at the poles?


texts: What kind of equilibrium constant we use for Gibbs free energy and Van't Hoff equation?

texts:
We know that the Gibbs free energy is related to the equilibrium constant by the following equation:
$$\Delta_\mathrm{r}G^\circ=-RT\ln K$$
We also know the Van't Hoff equation:
$$\ln\left(\frac{K_2}{K_1}\right)=\frac{-\Delta H^\circ}{R}\left(\frac{1}{T_2}-\frac{1}{T_1}\right)$$

$\left(R = 8.314\ \mathrm{J~mol^{-1}~K^{-1}}\right)$

My question is: what kind of $K$ do we use for these equations? Concentration quotient ($K_c$) or pressure quotient ($K_p$)?


texts: Do the products in exothermic reactions have higher kinetic energy than the products? Do they also have lower chemical energy?

texts:
I understand that in an exothermic reaction energy is transferred to the surroundings. More energy is produced from making bonds than absorbed to break bonds.

I would imagine that the products have lower chemical energy (bond energy perhaps?) but have higher kinetic energy as measuring the temperature of the surroundings is effectively measuring the kinetic energy of the specific molecules? I only doubt myself because on enthalpy change graphs the products are always lower than the reactants in an exothermic reaction, so increasing KE doesn't seem likely. If someone could clear up my confusion that'd be great!


texts: Why does this reaction proceed this way?

texts:
I am confused as to why this molecule changes its structure.
Also, I am confused why instead of OH, CHO is attached.

I would have thought that the double bond would break and OH would attach at each end via syn addition.The example:

Shouldn't this be the answer?


texts: Reduction of nitrobenzene with LiAlH4 and NaBH4

texts:
After searching a lot on the internet I've found that nitrobenzene is reduced by LiAlH4 to the following compound whose naming I couldn't do.

I couldn't find the mechanism for this reaction anywhere.
Can someone tell what is the mechanism for it?


texts: Isoptope effect on electrophilic aromatic substitution

texts:
My book reads

  Sulphonation will be the most effected electrophilic aromatic substitution reaction when benzene is replaced by hexadeutrobenzene.

I am not able to figure out how. All EAS reactions proceed by formation of an arenium ion and then the loss of an $H^+$ ion to regain aromaticity so all of them should be equally effected ( textbook does not mention how they are effected). I feel the only effect should be due to difference in bond enthalpies of $C-D$ bond and $ C-H$ bond.

I came across this reaction mechanism from chemlibretexts:

The hydrogen released is taken up by the $-SO_3H^-$

Can someone explain how and in what ways the replacement of hydrogen by deuterium effects the reaction ?


texts: Which is the currently accepted mechanism of a Wittig reaction?

texts:
The Wittig reaction is one of the most significant advances in synthetic organic chemistry in the 20th century and rightfully won its discoverer, Georg Wittig, the Nobel Prize in Chemistry.

A Wittig reaction is the addition of a phosphorus ylide (previously thought to be an ylene with a $\ce{C=P}$ bond) to an aldehyde or a ketone resulting in a $\ce{C=C}$ double bond.

Mechanistically, there is little debate that the final step is a cycloreversion of an oxaphosphetane liberating a phosphane oxide. However, as far as I know there is no agreement on the preceeding step(s) to form said oxaphosphetane; with two different competing mechanistic proposals:

Nucleophilic attack of the ylide onto the carbonyl carbon to give a charge-separated betain structure. This rotates around the newly-formed $\ce{C-C}$ bond until oxide and phosphonium are in proximity whereupon a bond is formed to close the oxaphosphetane (stepwise mechanism)
[2+2] cycloaddition of the ylide and the carbonyl to immediately form the oxaphosphetane in a concerted manner.

Wikipedia just presents these two mechanisms side by side hence it is not really helpful.

Which of the two mechanisms is, at present, considered the most likely reaction pathway? Which principal pieces of evidence point towards it and disfavour the competing mechanism?

Please answer including references to the corresponding journal articles.


texts: How is fluorine gas contained and transported, why aren't the metal cylinder and tube in this video attacked?

texts:
I included the GIF below as part of an answer to Can paper burn without oxygen or air?. It was made from the video Fluorine - Periodic Table of Videos.

I noticed that the cylinder containing the fluorine gas "filled up on the roof" in the video looks like it is made out of metal, as is the tube feeding the gas to the combustion sample.

The liquification experiment also shown in the video uses a flexible tube that appears to be plastic.

I know hydrofluoric acid will dissolve gas, but can dry fluorine gas be contained in glass? Since metals, even precious metals are generally attacked by fluorine, how is it stored, and how are the metal cylinder and tube in the video not also consumed?

Incidentally you can look up individual elements on Periodic Table of Videos at http://www.periodicvideos.com/


texts:
I want to ask a question about the MO diagram of BN.

I was provided with the following question and answer and describe the situation occurring:

After performing the s-p mixing for BN, I found this diagram worked as the $\ce{1\pi}$ MO was the HOMO, but I thought using atomic structure knowledge that as B and N are in the same group, and N has a greater nuclear charge (and hence greater effective nuclear charge) its orbital size would be smaller, not bigger as the diagram shows above.

Am I right in saying that the label above for these orbitals are wrong, so it should be showing $\ce{N-B}$ from left to right?

The whole question is given here below


texts: I've seen in a lot of books that biphenyl is not planar. I don't know why that is because both the carbon are $\mathrm{sp^2}$ hybridized so it should be planar. Can someone explain it to me?


texts: What type of reaction is this? (Modified organic nucleoside synthesis)

texts:
What type of reaction is shown in step F of this patent image?
I tried looking it up in SciFinder, but I didn't get any results, and I have not seen this before.

Thank you!
Edit 1: I'm also wondering if there is a specific name for this reaction, so that I can look it up.
Edit 2 Yes I'm sorry I forgot the reagents. The patent number is WO2014078463A1 (Bennett et al.) and I included a screenshot below of the relevant description.


texts: 1,4 addition to α,β-unsaturated carbonyls?

texts:
This is a numbering problem.

This is a 1,2-addition to an α,β-unsaturated carbonyl:

This is a 1,4-addition to an α,β-unsaturated carbonyl:

I don't see why the second reaction would be called 1,4. I'd call it rather 3,4, so obviously I am not getting the numbering rule. Help?


texts: What's the source of "2.303" in Van't Hoff equation?

texts:
I've seen a "2.303" term multiplied to $R$ in Van't Hoff equation several times.

Here is one example:

http://en.wikipedia.org/wiki/Van_%27t_Hoff_equation#Error_propagation

  $$\Delta H^\circ=2.303R\frac{\log K_1-\log K_2}{\frac1{T_2}-\frac1{T_1}}$$

What is this number and where does it come from?


texts: Atomic emission spectra: classical vs. quantum mechanics

texts:
In class, we were first introduced to classical mechanics, and how Bohr used the hydrogen electron to explain the atomic emission spectrum of that element. And it made sense. But then classical mechanics fails to explain other things, so we jump to quantum mechanics. And we learn about Newton's ideas of particles of light, and how Einstein said that light quanta are called photons, and how Louis de Broglie suggested that particles of matter can also behave like waves.

But I'm frustrated because, while the book does explain the history of quantum mechanics and the Heisenberg uncertainty principle, it doesn't explain how quantum mechanics has anything to do with atomic emission spectra. So my question is, how does quantum mechanics explain the atomic emission spectrum of elements better than classical mechanics does?

And how much of classical mechanics fails to account for what quantum mechanics does? So is the idea that an electron moving from one high energy level to a lower energy level in an atom releases energy/light is only true for hydrogen, and false for all the other elements? How can this be true?


texts: How do I determine the equilibrium concentration given Kc and the concentrations of component gases?

texts:
I feel my method for solving it is correct and I've checked my calculations yet I can't get the right answer.

Nitrogen and oxygen gases may react to form nitrogen monoxide. At 1500 °C, $K_c$ equals 1.0E-5.

$\ce{N2_{(g)} + O2_{(g)} <=> 2 NO_{(g)}}$

If $2.75 \times 10^{-2}$ mol $N_2$ and $2.75 \times 10^{-2}$ mol $O_2$ are sealed in a $0.886 L$ flask at $1500 °C$, what is the concentration of $\ce{NO_{(g)}}$ when equilibrium is established?

Notes: $K_c$ = equilibrium constant

a) 1.38E-7 M
b) 4.35E-5 M
c) 3.85E-5 M
d) 8.70E-5 M
e) 2.30E+4 M

I set up the problem with $(2x)^2$ as a numerator and $(.03104 - x)^2$ as the denominator

I took square root of both sides and did algebra and got $4.9*10^{-5}$

For the record the answer is $8.7 \times 10^{-5}$


texts: Why the products of combustion of Cu2S are Cu2O and SO2?

texts:
$$\ce{Cu2S + 2 O2 -> 2 CuO + SO2}$$

Why are not these oxides $\ce{Cu2O}$, $\ce{SO}$ or $\ce{SO3}$?
Is it connected to the stability of these molecules?


texts:
Can bromide ion reduce ferric ion ?

Just a query.
In my opinion it can since bromide ion can undergo oxidation.
Is my answer correct?


texts: Does increasing # of hydrogen bonds decrease the strength of these bonds?

texts:
I saw the question, "Is the strength of hydrogen bonding greater in hydrogen peroxide or water?" and it made me think of a question on hydrogen bonding:
If an oxygen on a water has a hydrogen bond to another water (or anything else), would adding another hydrogen bond to that water (perhaps by introducing another water), decrease the strength of the first hydrogen bond?
My initial thought is it that it wouldn't because oxygen is electronegative enough that is can attract another hydrogen bond with minimal effect to the other bond.
However, if a single water could attract an unlimited number of other waters to it (ignoring space constraints), wouldn't the strength of hydrogen bonds weaken as the number of bonds to the oxygen increase as it's dividing up its electronegativity across multiple bonds?


texts: Helmholtz Free Energy Minimization Proof

texts:
In the proof that Helmholtz free energy is minimized at equilibrium, we use the fact that $$\mathrm dS_\text{total}=\mathrm dS_\text{system}+\mathrm dS_\text{bath}\geq 0$$
But we also use the fact that
$$\mathrm dS_\text{bath}=\frac{\mathrm dU_\text{bath}}T=-\frac{\mathrm dU_\text{system}}T$$
Why does this not imply that $\mathrm dS_\text{system}=\frac{\mathrm dU_\text{system}}T$ and therefore $\mathrm dS_\text{total}=0$?
Is this because only the bath is always at temperature $T$, so we can imagine a reversible path, whereas the system may have some temperature fluctuations during the process of heat exchange with the bath?


texts: Chemical incompatibility between aluminum hydroxide [Al(OH)3] and carbomer polymer [-CH2-CH] N-COOH]

texts: I am currently adsorbing proteins to an aluminum hydroxide gel.  By adding a carbomer (polymer of acrylic acid cross-linked with allyl sucrose), I achieve a somewhat synergistic formulation.  Shortly after adding the carbomer, a granular precipitate forms that adheres to glass.  Questions: 1) What is this precipitate?; 2) Will my adsorbed protein release from the aluminum hydroxide after carbomer addition?; 3) Is there possible long-term instability of this mixture?  Thank you!


texts: Is there a method to separate ions from water other than by double displacement precipitation?

texts: I'm working on a problem for school where we have to detect Fe3+, Ca2+, Cl-, and SO42- ions in water, and we have been given AgNO3, KSCN, BaCl2, and a HC2H3O2/Na2C2O4 mixture (all in solution) to do so. We have already determined the ion content by precipitating them out using successive double displacement reactions, but we also have to do it using another method. Is there another way to separate or detect ions in solution?


texts: What is the priority for numbering alkyl side chains?

texts: I'm wondering why the above image is named 5-ethyl-3,3-dimethylheptane rather than 3-ethyl-5,5-dimethylheptane. I thought an ethyl substituent has a higher priority (I know this is true when arranging the final name, but what about numbering the parent chain)?


texts: Kinetics of a simultaneous parallel radioactive decay

texts:
Question:

A radioactive isotope, A undergoes simultaneous decay to different nuclei as:
\begin{array}{cc}
\ce{A->P}&\,(t_{1/2}=9\ \mathrm h)\\
\ce{A->Q}&\,(t_{1/2}=4.5\ \mathrm h)
\end{array}
Assuming that initially neither P nor Q was present, after how many hours, amount of Q will be just double to the amount of A remaining?

My solving:
I got the $t_{1/2}$ for $A$ as $T=\dfrac{T_1T_2}{T_1+T_2}\ =\pu{ 3 h}$
Now from Rutherford-soddy law the number of atoms left after $n$ half lives are,
$$N=N_0\left(\frac{1}{2}\right)^n$$
and number of half lives $n=\dfrac{\text{Total time of Decay}}{\text{effective half life}}$
For isotope $A$, $\dfrac{N_A}{N_{0_A}}=\left(\dfrac{1}{2}\right)^{n}=\left(\dfrac{1}{2}\right)^{T/3}$ where $T$ is the common time of decay for $\mathrm A$ and $\mathrm Q$
For $\mathrm Q$ I had to assume that $\mathrm Q$ is also undergoing radioactive decay to form a relation between $\mathrm A$ and $\mathrm Q$
Now using the same formula as above $\dfrac{N_\mathrm Q}{N_{0_\mathrm Q}}=\left(\dfrac{1}{2}\right)^{T/4.5}=\left (\dfrac{1}{2}\right )^{2T/9}$
Now applying the condition in the question, $$\left (\frac{1}{2}\right)^{2T/9}=2\cdot \left (\dfrac{1}{2}\right)^{T/3} $$
Raising by power $9$ on both the sides,
$$\left (\dfrac{1}{2}\right )^{2T}=2^9\cdot \left (\frac{1}{2}\right )^{3T}$$
which implies,
$$ 2^{-2T}=2^{9-3T}$$
Therefore,
$$9-3T=-2T$$
$$
{\bbox[10px, border:2px solid red]{
 T=9\ \mathrm h.
}}
$$
Although I have got an answer and it satisfies the condition I still think it's wrong because of the assumption made for $\mathrm Q$ and something else needed to be done to make the relation between $\mathrm A$ and $\mathrm Q$ Moreover, it's given in the question that initially neither $\mathrm P$ nor $\mathrm Q$ was present and I guess the assumption violates that.


texts:
I recently setup a heating apparatus for the large antechamber in my glovebox (i.e., large amounts of heating tape). Eventually, I want to do bake-outs for my moisture-sensitive chemistries (e.g., battery electrolytes).

What is the standard procedure for bake out in an antechamber? I know that many commercial entities like mBraun sell heating add ons for their boxes, so I'm sure that best practice exists.

Is it best that I put the chamber under slight vacuum so that pressure doesn't build up? Is it best that I keep argon in the chamber to help with heat transfer? What are other considerations I should have when running a bake?


texts: Spacing between adjacent planes of a given set in a simple cubic crystal

texts:
Today I learned about Miller indices in a cubic crystal, and I learned that adjacent planes $(hkl)$ in a simple cubic crystal are spaced a distance $d_{hkl}$ from each other, with $d_{hkl}$ given by:

$$d_{hkl} = \frac{a}{\sqrt{h^2 + k^2 + l^2}}$$

For example, take the origin any of the below vertices of the cube with z axis directed upwards, the $(0 0 2)$ plane cuts horizontally the middle of the cube, and for this set of planes, $d_{hkl} = \frac{a}{2}$.

May be a silly question, but if we followed the rule of spacing, we would get that the next $(0 0 2)$ plane is the very upper horizontal plane in the cube, which - i guess - is not true since the latter plane has $(0 0 1)$ and not in any case $(0 0 2)$ miller indices. However, if we considered that $(0 0 2)$ planes are only those passing horizontally through the middle of unit cells, then the distance between them will equal $a$ and not $\frac{a}{2}$ (using imagination and not rules).

I must be missing something very trivial here, but it is only today that i started learning these stuff and i am really confused. Thanks for help.


texts: Why stepwise dissociation for acids but not hydroxide bases?

texts:
My son asked this over the weekend and I didn't have a good answer: how come with polyprotic acids we assume that the release of each $\ce{H+}$ is progressively harder, but with bases like $\ce{Ca(OH)2}$ we write $\ce{Ca^2+}$ and $\ce{2OH-}$ as the products?

What I know about, say, sulfuric acid, seems to suggest that when we put calcium hydroxide in water we should get $\ce{CaOH+}$ and a single hydroxide, and it should be much harder to release that second hydroxide.  What am I missing?


texts: Why does the helium hydride ion have such a large dipole moment?

texts: According to Wikipedia, the helium hydride ion $\ce {HeH+}$ has a dipole moment of 2.26 or 2.84. What contributes to this large dipole moment in this molecular ion?


texts: Finding out the composition of seawater/brine?

texts:
As part of a project, I am working on precipitating salts from seawater and brine. I have a sample of seawater and I need to measure the concentrations of $\ce{Mg^2+, Ca^2+ and Li+}$ present in the sample. As well as being able to measure $\ce{MgCl2, CaCl2 and LiCl}$.

What analytical instrument would be best for this experiment? We have a decent budget but dont want to invest in equipment too large (i.e ICP-AES or ICP-MS) as the laboratory isnt very big.

I have looked into ion-chromatography and can get one for about 20k USD, anyone else got any better ideas or reasons not to go for ion chromatograph?


texts: Why when I add jam to my tea it stops producing thin "membrane" on top?

texts: Thin "membrane" is created if I leave cup of tea for hour or more. And it usually sticks to the inner sides of the cup. But I noticed that when I drink tea with jam or syrup then the cup always clean inside as if the syrup contains some kind of acid that remove that tea-thingy.


texts: Decarboxylation mechanism and stability of α,β-unsaturated and α-hydroxy acids

texts:
I was wondering why α,β-unsaturated and α-hydroxy acids undergo decarboxylation. Also, I'm aware of neither the products nor mechanism. All I know is that β-keto acids and α-nitro compounds have resonance stabilized anions and have stable transition states.

But α,β-unsaturated have none of those and it isn't that electronegative as its sp2. Someone please help me out; I can't find the answer anywhere else.


texts: In Diazonium Ion why does N contain 4 bonds?

texts: Nitrogen's valenc number is 3. Sometimes it can form a co-ordinate bond by donating it's lone pair electrons. In diazonium ion N has 4 bonds, then one of those 4 bonds must be a co-ordinate bond. Actually I can't define the co-ordinate bond in diazonium ion.Again In diazonium structure, it is shown the first N with 4 bonds is positive but why??


texts:
I was taking a chemistry test and I encountered the following question:

  How many electrons can an orbital of type f hold?

  A. 6
  B. 10
  C. 2
  D. 14
  E. 1

Since there can be [-ℓ, ℓ] orientations and since the orbital type f has ℓ = 3, we should have 7 possible orientations with 2 spins, so ${7 \times 2 = 14}$, so I thought the correct answer was D (14).

However, I got it wrong and the correct answer is marked as C (2). Is it an error in the test, or am I missing something?


texts: IUPAC Nomenclature of Benzene+Aliphatic chain

texts:
What is this compound's IUPAC name?

1) 2-phenyloctane.
2) octan-2-ylbenzene.

Is using phenyl correct or is taking benzene as the base correct?


texts: Why does molten plastic (PLA) stick to metals (AL)?

texts:
I know this is broad so I will narrow:
Why does molten PLA stick to Aluminum?

I ask because I'm looking for a way to prevent/reduce the friction of the plastic inside the aluminum barrel of a 3D Printer. I believe that I can treat the surface of the aluminum with a High Temp enamel however I need to be sure of the physics of why the plastic sticks in the first place. Is it the surface finish, or is the molecular attractiveness? If it is the finish, then I can make it smooth. If it is static attraction then I can charge the barrel etc.


texts: What will eventually happen to uncovered vegetable (seed) oil exposed to the air?

texts:
If I leave some olive oil uncovered and fully exposed to indoors air for enough time (though away from UV exposure or any other environmental factors), what will happen to the oil?

I read here that some of its constituents ('lighter' molecules) will start to evaporate but that heavier ones will be left behind, which will 'not quite' evaporate.

If that is true (it may not be), would the non-evaporative part of the oil eventually harden and assume a cake-like consistency, almost like wax or hardened animal lard stored at refridgerator temperatures?


texts: Even one letter can make a huge difference in Chemistry Nomenclature. So I am looking for credible resources that is specifically published for explaining Nomenclature rules, examples in Spanish. Any suggestions?


texts: Why is the smell of car exhaust much stronger in winter?

texts: I noticed that in winter, the smell of cars (to be precise the smell of the exhaust gases) is much stronger in winter. I just can't figure out why. Has this got something to do with the air temperature or with the humidity?


texts: Symmetry representations for acetonitrile (CH3CN)

texts:
Can anybody share the symmetry labels for acetonitrile ($\ce{CH3CN}$), please?
I mean to assign the symmetry labels to orbitals of acetonitrile


texts: Explaining the oxidation states of palladium

texts:
Palladium follows an exception to normal electron filling-up rules and so has the electron configuration of $\ce{[Kr]  4d^{10} 5s^0}$

The oxidation states of palladium are $\ce{+II}$ and $\ce{+IV}$.
How can these oxidation states be explained by looking at the special electron configuration of $\ce{Pd}$?


texts: A book like Feynman's Lectures to Physics, which deals with Chemistry and provides insights

texts: I have been reading The Feynman Lectures, and it provides a lot of basic knowledge in physics. I would like to know if there exists a book for chemistry like this too.


texts: How to calculate the enthalpy change of water?

texts:
Calculate the $\Delta H$ of the reaction where $2.6\:\mathrm{g}$ of water, $C_\mathrm{s}= 4.184 \mathrm{\frac{J}{g\:K}}$ is heated, raising the temperature increases from $298\:\mathrm{K}$ to $303\:\mathrm{K}$.

I used the following equation: $\Delta H=mC_\mathrm{s}\Delta T$

$m = 2.6~\mathrm{g}$, $C_\mathrm{s} = 4.184~\mathrm{J/g}$, $\Delta T= 5$

What I got: $(2.6)(4.184)(5)= 54.392~\mathrm{J/g}$

Did I solve this correctly?


texts: What are the signs for work done by (on?) a gas during isothermal reversible compression?

texts:
For the expansion of a gas, isothermally and reversibly, what is the sign taken?
Do I use this equation
$-nRT\ln  (Vf/Vi)$
or this one
$nRT\ln  (Vf/Vi)$ ?
Moreover, when I'm asked about the 'work done', what exactly does the work? The gas itself? The surroundings? I'm confused about this because my text says one thing and the guidebook, another.
Thanks.


texts: What Would Hypochlorite Ions Prefer to React with, Hydrogen Ions or Ozone?

texts: If I had a box that had inside it a UV light an equal quantity of ozone ($\ce{O3}$), and $\ce{H3O+}$, which would be broken down because of the UV light to $\ce{O}$, and $\ce{O2}$, as well as $\ce{H2O}$, and $\ce{H+}$ because that is what the $\ce{H3O+}$ would be broken down into. If I introduced one hypochlorite Ion ($\ce{ClO-}$) or a chloride Ion ($\ce{Cl-}$), what would the chloride Ion or hypochlorite Ion react with? Would it react with the $\ce{H+}$, or the $\ce{O}$ & $\ce{O2}$?


texts: Base Peak Intensity different than higher value in Mass Intensity Map

texts:
I've been working with mass spectrum data analysis (but my field is computer science).

I'm using a library that allows me to get the entire Mass Intensity of the MS1 scan (such as [time, intensity]). However, by searching for the highest value for intensity, it is always a few integers lower than the base peak intensity.

I'm retrieving the information from a mzXML file, and the library that I'm using is ms-data-core-api. The method used to retrieve the intensity map, in case anyone has ever used this library, is this one: public double[][] getMassIntensityMap(). I retrieve the highest peek in the map by iterating the matrix returned and updating a variable with the highest value found in the y axis (given double [x = time][y = mass].

Examples of the difference of data include the following:

scan 1 (MS1): Highest peak in map: 789991.875 / base peak intensity: 793728.0
scan 2 (MS1): Highest peak in map: 714475.5  / base peak intensity: 719125.0
scan 3 (MS1): Highest peak in map: 673152.6875  / base peak intensity: 680567.0

From what I can tell, the instrument used for these scans is a fourier transform ion cyclotron resonance mass spectrometer, using Xcalibur as the  software.

Does this makes sense, and why?


texts: Why does my metal phone ring stand becomes iridescent, and turns back to normal after a while?

texts:
I got this metal phone ring stand from online. When I was meddling with it, I notice the ring started to produce iridescence. (See photo-only the centre portion, the moveable ring is not affected) I believe the mild heat from my hand caused this to happen. I left it alone on a table overnight, and the next morning, the iridescence disappeared. Te ring is back to normal.

Whenever I applied mild heat again (I placed it at the back of my vacuum cleaner for 5seconds), the iridescent will appear, but will then disappear again after I leave it overnight.

The iridescent consists of greenish, pinkish and purplish hues. It doesn’t seem to be forming at the surface, but rather it seems to be forming in the interior.

The seller claims that the ring is made up of zinc alloy, but it is magnetic. Some guesses of the material that might be in the product: zinc alloy, nickel, steel, chrome plating (the centre portion is very reflective like a mirror) Please correct me if my guesses are wrong.

I am just very perturbed by this phenomenon occurring in such simple object and am curious to find out what causes this!!

Thank you!!


texts: Why would decreasing ionic strength of buffer disrupt hydrogen bonds

texts:
I'm reading about cDNA synthesis in my textbook and it mentions that:

  The captured mRNAs are subsequently released and collected, for example, by decreasing the ionic strength of the buffer so that the hydrogen bonds will be disrupted

So my question is why would this happen? What does the ionic strength of the buffer have to do with the hydrogen bonds the mRNA has formed?


texts: Is 4-nitrobenzaldehyde or 4-aminobenzaldehyde more likely to be hydrated?

texts:
Of 4-nitrobenzaldehyde and 4-aminobenzaldehyde, which has the higher $\ce{K_{eq}}$ of hydration?

 $\qquad \qquad$

Steric factors can likely be ignored in this problem since we are dealing with rather structurally similar compounds.

I suspect the problem comes down to recognizing that a more polar compound is more favorably solvated by water.

I know that the nitro group is always electron-withdrawing, and I drew a few resonance structures as well. The resonance structures for both, however, seem to suggest that both are rather polarized (given the distribution of formal charges).

Resonance forms for 4-nitrobenzaldehyde

I expect the ones with the oxygen possessing the incomplete octet are very minor resonance contributors.
Therefore it seems that the main thing about this molecule is that the nitro group is withdrawing electron density from the ring and the aldehyde group.

Resonance forms for 4-aminobenzaldehyde

The resonance structures here are all somewhat reasonable.


texts: Carbocation rearrangement involving three membered rings

texts:
Question:

Taking into account of various carbocations and, as well as the rules governing mechanisms of carbocation rearrangements, which reaction is most likely to occur during the given reaction?

My take on the question was this mechanism:

I'm torn between this mechanism and option (b). How do I judge between anchymeric assistance  and stabilization of the intermediate through 5 alpha hydrogens. How will the carbocation rearrange?
Source: MS Chouhan, Chapter: Alkenes, Q.17
This inadequate solution was given:


texts:
Superheated water refers to water that is heating well beyond its usual boiling point under extreme pressure. This cause it to display anomalous property.

I noticed that as temperature increases, so does the self-ionization of water, that is, the concentration of $\ce{H3O+}$ and $\ce{OH-}$.

It appears to me that the above phenomenon is caused by increased "freedom of movement" in hydrogen cation, or protons, allowing them to leap from one charge-neutral molecule to another, ionizing both their source and destination.

My question is, what would happen if the pressure and temperature of water is taken to the extreme? Would there be sufficient kinetic energy in the material to allow essentially free movement of $\ce{H+}$ among particles of $\ce{O^2-}$? Which makes it so that the water essentially behave like a plasma consisting of the two types of ions? Or would the energy required to reduce $\ce{OH-}$ be so enormous that some other phenomenon will take place before this is possible?


texts: What is the meaning of an oxide being 'Higher' or 'Lower'?

texts:
To put it simply, many books use the term 'Higher Oxide' or 'Lower Oxide'.

What does this mean?


texts: Why do better π-acceptor ligands cause smaller Δ(T) d-orbital splitting?

texts:
Consider a formazanate ligand. Then imagine an electron-withdrawing group added to it. I expect a small σ-donating effect, and good π-accepting properties.

My supervisor tells me that an electron-withdrawing group causes a lowering of the π*-orbital energy, leading to a smaller $\Delta_\mathrm{T}$ in the d-orbital splitting of the resulting iron-based molecular orbitals. Why would this be the case?


texts: Is it correct to say that ethenol is an alcohol?

texts:
IUPAC Gold Book defines alcohols as:

  Compounds in which a hydroxy group, $\ce{–OH}$, is attached to a
  saturated carbon atom $\ce{R3COH}$.

However, Wikipedia says that:

  Vinyl alcohol, also called ethenol (IUPAC name), is an alcohol.

Is Wikipedia wrong about this?

And if ethenol is not an alcohol, what would be the correct name for compounds in which an $\ce{–OH}$ group is attached to an unsaturated carbon atom?


texts: Why does Pb have a higher electronegativity than Sn?

texts:
I recently learnt that electronegativity generally decreases as I move down a group and from right to left within a period. However, according to the table below, Pb has an electronegativity of $2.33$, which is higher than $1.96$ of Sn. There are also a lot other elements, such as Au, Hg, and W, that does not follow the general rule of electronegativity.

  Can someone offer an explanation of why some elements have a higher electronegativity than the elements directly above them?


texts: Will disodium EDTA effectively destroy Tollens' reagent?

texts: As I understand it, if I mix $\ce{[Ag(NH3)2]NO3}$ and $\ce{Na2EDTA}$ the silver will complex much more strongly with the EDTA than the ammonia, and the hydrogen ions will protonate the ammonia, leaving $\ce{AgEDTA^{3-} + 2NH4+ +NO3- + 2Na+}$, preventing the formation of silver nitride. Does that make sense? I'm concerned that the nitrate is incompatible with the EDTA somehow (that is, that it will oxidize something and break it apart).


texts: Is the following rate law possible for the given reaction?

texts:
A researcher is investigating the following overall reaction:
$$\ce{2C + D -> E}$$
The researcher claims the rate law for the reaction is written as follows: $\text{Rate} = k[\ce{C}][\ce{D}]$.

Is the rate law equation possible for the given reaction?
If so, suggest a mechanism that would match the rate law. If not, explain why not.

The answer is yes. I don't know how to arrive at this answer. From what I  have learned, the following must be true for a) to be true:

The rate law for the slow step agrees with the experimental rate law
The elementary steps of add up to the overall reaction.

I would assume the following elementary steps from the rate the researcher has confirmed:
$$
\begin{align}
\ce{C + D &-> CD}\\
\ce{C + CD &-> E}
\end{align}
$$
But since $\ce{CD}$ has a larger size than $\ce{D},$ wouldn't it be less likely to have the proper alignment in a collision to enter the active state? Thus, wouldn't it be a slower reaction than $\ce{C + D}?$
Please inform me where my logic is wrong and why the answer is yes.


texts: Why is chloridric acid used in salt bridges?

texts:
I've been planning an experiment on how to make galvanic cells and during my research I came across an article in which chloridric acid was used, along with a soluble salt and agar-agar,  in salt bridges.
Since then, I've been wondering why chloridric acid was added to agar-agar.

Thanks in advence.


texts: In what order should the compounds containing Ru and Os, or Mo and W be named?

texts:
According to IUPAC recommendations for naming of inorganic compounds, the more electropositive element is written first with a suitable prefix, and the more electronegative element is written at the last with a suffix -de and a prefix. For example, $\ce{H2O}$ (Water) can be called dihydrogen monooxide. [this is an modified statement extracted from the wiki encyclopedia-IUPAC nomenclature of inorganic chemistry]
  In the above example, $\ce{H}$ (Pauling scale = 2.20 or Allen scale = 2.300) is less electronegative than $\ce{O}$ (Pauling scale = 3.44 or Allen scale = 3.610). So, $\ce{H}$ is placed first, followed by $\ce{O}$.

If suppose we were needed to name the compounds containing

$\ce{Ru}$ (Pauling scale = 2.2) and $\ce{Os}$ (Pauling scale = 2.2)
$\ce{Mo}$ (Allen scale = 1.47) and $\ce{W}$ (Allen scale = 1.47)

, in what order should we write the elements?

If we use pauling scale as referance, we would face difficulty in naming $\ce{Ru}$ and $\ce{Os}$, if we use allen scale, we would be in trouble with respect to the elements like $\ce{Mo}$ and $\ce{W}$, etc, as we can see that elements have same electronegativity value. I don't know whether the compounds with the above mentioned elements exist or not, but if we suppose, assume that, they exist, in what order should they be named?


texts: I'm looking for a reducing sugar such as glucose or maltose (any reducing sugar will do) for some home chemistry experiments. Is there a readily available reducing sugar that I might source without contacting a chemical company? A simple "synthesis" of glucose from sucrose would work as well.


texts: In a weak acid-strong base titration why is [H+] no longer equal to [A-] after addition of the base? (A2 level chemistry)

texts:
I understand that before any base is added $\ce{[H+]}$ is equal to $\ce{[A-]}$ but why is $\ce{[H+]}$ no longer equal to $\ce{[A-]}$ when the strong base is added?

If all the following reactions below are occurring in solution and both $\ce{CH3COO-}$ an $\ce{H+}$ are able to react in either one of two of these different reactions then why should the $\ce{[H+]}$ no loner equal $\ce{[A-]}$ if both have equal opportunities to be consumed? (I am aware that not all the $\ce{CH3COOH}$ will have dissociated but surely this would not affect the concentrations of either $\ce{[H+]}$ or $\ce{[A-]}$?)

$$\ce{Na+ + CH3COO- -> CH3COONa}$$
$$\ce{CH3COO- + H+ -> CH3COOH}$$
$$\ce{H+ + OH- -> H2O}$$

Is it because the salt $\ce{CH3COONa}$ is much more likely to dissociate than $\ce{CH3COOH}$ and $\ce{H2O}$ meaning more $\ce{CH3COO-}$ remains in solution than $\ce{H+}$?


texts: Acidity comparison between cyclopropene and cyclopropane

texts:
There many sources on the internet saying that cyclopropane is more acidic than cyclopropene because the conjugate base in latter would have antiaromaticity which would destabilize it.

But in this explanation we are assuming that the central $\ce{C-H}$ bond in cyclopropene ionizes. I argue that the $\ce{C(sp^2)-H(s)}$ bond should ionize because of two factors:

The $\ce{sp^2}$ carbon would better accommodate the negative charge than the central $\ce{sp^3}$ carbon.
Consequent conjugate base would not contain anti aromaticity.

My logic can also be rationalized by considering acidity order between straight chain alkanes and alkenes.

This would mean inversion of the order which is incorrect according to experimental data. What is the flaw in my reasoning?


texts: Is sodium nitrate a covalent or ionic compound? This is a test question. I put the answer ionic compound but my teacher says that statement is false because it is only partially ionic as there is covalent bond between nitrogen and oxygen in the nitrate ion. Is that true?


texts: What is the principle of “scrubbing” in liquid extraction or solvent extraction?

texts:
There are many steps in solvent extraction:

Extraction
Scrubbing
Back extraction

I understand the 1st and the 3rd.
What is the principle of scrubbing?
Is it just washing the organic phase?
How undesirable species get removed from organic phase?


texts: How to label atoms or groups "backwards" in ChemDraw

texts: I'm trying to draw L-tyrosine with the hydroxyl part of the phenol as HO instead of OH as it appears in the ChemDraw image. Everytime I type in HO, it automatically corrects to OH. I have the settings in ACS Document 1996 style. Is there anyway to make the format render my "backwards" type?


texts: Reaction mechanism of imine reduction to amine using an aluminium amalgam

texts:
I can not find any good resources on the Internet except for some shady drug syntheses. I was hoping that someone could provide me with some more educational information.

I'm interested in imine-amine reduction methods, but it was hardly discussed in my class. It would be very nice if someone could explain the exact reaction mechanism of the imine-amine reduction in the presence of an aluminium amalgam.

I also found that the very dangerous compound Mercury(II) chloride was used a lot in this method and I was wondering why for example Mercury sulfide is not used, as I thought it would be a lot safer since it is hardly soluble in water and is therefore less likely to do any physical harm.


texts:
Can you tell me what is a burst nucleation process, and how can it be used for synthesising uniform nanoparticles?

Can you also provide (if possible) any links to papers or materials regarding mechanism of nanoparticles growth?


texts: Do chemists refer to water as "dihydrogen monoxide"?

texts:
Is the name "Dihydrogen monoxide" actually what chemists would use to refer to $\ce{H2O}$ (assuming there was no common name, "water")?

Of course, this is all over the internet. I'm a little skeptical though because the similar chemical $\ce{H2S}$ is called "hydrogen sulfide", not "dihydrogen monosulfide".


texts:
Different websites say different things on the matter.

 For example:

 This Website   Holds that pitchblende is also known by the name Uraninite.

This Website   Holds that pitchblende is a type of Uraninite.

My question is, which website is correct? I have always known the first site to be a reputable source, so I assume that this is a contentious topic.


texts: Investigating a factor affecting buffer capacity

texts:
I'm preparing for an experiment to investigate some factor affecting buffer capacity. At the moment, I'm looking at using a $\ce{NH_3}$ ($2\,\mathrm{M}$) $+$ $\ce{NH_4Cl}$ buffer, but I'm not sure which factor to test. My research tells me that only the concentrations of each will affect buffer capacity, and that the ratio of their concentrations will affect the $\mathrm{pH}$ of the buffer (by the Henderson-Hasselbalch equation). Are there other factors which I can test, because I'm trying to make it a bit more interesting? As far as I can tell, something like temperature won't affect buffer capacity.

As far as the actually experiment goes, what would be the best way to measure buffer capacity? I could just do a titration and record the $\mathrm{pH}$ as I go, but I'm thinking of using an indicator and measuring absorbance. I'm open to any ideas here, because I'm struggling to think of anything "out of the box"?


texts: Does Fluoroborate gets used up in Electroplating

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I've been working on Tin electroplating on the side for a while now. I've formulated a mix from my usual electroplating formula template. The mix stubbornly keeps on having the Tin ions form Tin Hydroxide with water. I've tried adding different organics and complexes in hopes of preventing this. But the Hydroxides keep on forming and so the mix does not provide enough Tin ions to allow electroplating at relatively low voltages (at least 16V DC is necessary).

So I finally relented and poured in my "Liquid Tin" http://www.mgchemicals.com/downloads/pdf/specsheets/421.pdf into the mix. Liquid Tin has Stannous Fluoroborate and its the Fluoroborate that keeps the Tin from forming Hydroxides. The effect was really good as plating happens at less than 1V, but then again Liquid Tin is for Electroless plating. After a while it needs higher voltage to electroplate.

So that got me wondering, does the Fluoroborate ion get used up in Electroplating? If there's a danger with Fluorine gas escaping, please also tell me.


texts: Which of the following elements forms a water-soluble, alkaline oxide?

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An element burns in oxygen to form a solid oxide which dissolves in water. The pH of the resulting solution is greater than seven. Which one of the following could the element be?

A. sulphur

B. phosphorus

C. magnesium

D. sodium

E. carbon

The right answer is sodium. But I don't really understand why it can't be magnesium as well.


texts: Assumptions made in calculating melting point from thermodynamic data

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I'm fine with doing these questions, such as:

For ammonia, enthalpy of fusion is 5.65 kJ/mol, and entropy of fusion is 28.9 J/K.mol

Hence find an approximate melting point:
Well $\Delta G = \Delta H - T\Delta S = 5.65*10^3 - T(28.9)=0$ Which yields $T=196K$. This is quite close to Google's value.

What I'm thinking, though, is that we shouldn't be able (in real life) to determine a melting point so easily, because $\Delta_r H$ and $\Delta_r S$ both vary with temperature, so in reality this isn't as simple as solving a linear equation for T?

I'd just like some confirmation here, as my textbook isn't giving much away on this point :)


texts: Why isn't hydrochloric acid typically made via the photochlorination of hydrogen?

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I understand that in large quantities the reaction is explosive but couldn't the flow of gas just be regulated to control the reaction? It seems like producing hydrogen chloride like this then dissolving it would be a very straightforward way to make hydrochloric acid.

To clarify, when I say 'typically' I mean on an industrial scale.


texts: Measuring volume change from change in mass

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I want to measure the expansion (by change in volume) of a material in liquid. However the shapes are so complex that I can only measure their mass. Is it possible to compute the volume of the expanded shape by measuring its mass alone?

Given mass $m_0$ at $t_0$ and mass $m_1$  at $t_1$ and the density $\rho_\mathrm m$ of the material and $\rho_\mathrm l$ of the liquid, can I find the volume change of the object from $t_0$ to $t_1$?

One could assume that $(m_0-m_1)/\rho_\mathrm l$ is the correct answer, but I am not sure if this is the right way to go about it?


texts: Theoritical amount of Sodium Bicarbonate

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I have to find the theoretical amount of sodium bicarbonate. The steps I followed in order to produce it are:

15g $\ce{NaCl}$ are added to a beaker. Then we add 87.5 mL of $\ce{NH3}(12M)$
We add 115g of dry ice(whose density is 1.5 g/mL)
Then the solid is taken with filtration and we rinse it first with 9mL of cold water and then with 6mL of acetone.

Then we put the solid in the oven. I know that the product after we take it off the oven will be sodium bicarbonate.
I believe that in order to find the theoretical amount of sodium bicarbonate I have to write down the reactions that are taking place.

$\ce{NaCl + NH_3 + CO_2 + H_2O → NH_4Cl + NaHCO_3}$

But I'm confused as to if there is another reaction where $\ce{NH_4Cl}$ and $\ce{NaHCO_3}$ react with water or acetone. Also, working with the stoichiometry of the reactions, from which reactant is it better to conclude about the moles of NaHCO3?


texts: I've been manipulating certain chemical properties and I've come up with a new formula that doesn't seem to already have been discovered. How would I go about publishing my findings?


texts: What are the alternatives to the Periodic Table of the Elements?

texts: What are the different diagrams/tables used to organize the elements other than the Periodic Table? What are the advantages/disadvantages of each?


texts: Fluoride concentration in LiF and CdF2 solutions

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Trying to learn how to use $\ce{K_{\mathrm{sp}}}$ values and not understanding. See question below:

Two saturated aqueous solutions are prepared at $\pu{25^\circ C}$
Solution1 is made by dissolving cadmium fluoride ($\ce{CdF2}$, $\ce{K_{sp}} = \pu{6.44E−3}$) in $\pu{100.0 mL}$ of water until excess solid is present.
Solution 2 is prepared by dissolving lithium fluoride ($\ce{LiF}$, $\ce{K_{sp}} = \pu{1.84E−3}$) in $\pu{200.0 mL}$ of water until excess solid is present.
Which solution has a higher fluoride ion concentration?"

I used the $\ce{K_{sp}}$ given for $\ce{CdF2}$ to get $s = 0.11720$, so $\ce{[F]} = 2s = \pu{0.2344 M}$, is that right? I guess I'm not sure what to do after that to get find the concentration in $\pu{100 mL}$.  Wouldn't it be $\pu{2.344 M}$?  I am told this answer is incorrect.


texts: Resonance of lone pair of nitrogen in 4‐nitroaniline and piperidin‐2‐one

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While working out some questions on comparing the basic nature of various compounds, I came across the following two compounds:

In case of A I could see several resonating structures, and also the −M effect of the nitro group. So justifying based on the number of resonance structures, I could tell that the lone pairs are more delocalized in A than in B. Hence B is more basic.
However, on verifying my answer I found that A was more basic.
The only reason I could come up with is that in compound A, majority of the resonance includes a negative charge on carbon, but in compound B, the negative charge lands on the more electronegative oxygen, which better succeeds in stabilizing it.
But it doesn't seem right for me.
Can anyone please tell me the correct reason for this?


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I need to make a solution that has a 15% (wt/wt%) HCl acid concentration and a 6% (wt/wt%) NaI concentration. I'm not sure yet how much of this solution I will be required to make so a general recipie would be awesome.  I would also like to know how to make the concentrations wt/vol% as well.

Additional information:

I have a bottle of Muriatic Acid. Its label says the contents are HCl acid, 20 degree Baume (31.45% by weight). The product's MSDS sheet says its 65-75% water and 25-35% HCl, and its specific gravity is 1.16 (1.16 g/ml).

I have Sodium Iodide (a brick of it). Its label says 99+%, pure, anhydrous.


texts: heat capacity at constant volume and internal energy

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I read that heat supplied at constant volume to a system containing ideal gas changes the internal energy of system i.e $q=n C_v \Delta T= \Delta U$

But what happens if I heat a system and change its temperature from $T_1$ to $T_2$ with system not being at constant volume,can I still say that $\Delta U = n C_v \Delta T$?
Is there any proof regarding this?