20
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What is the mechanism of the reaction between hexane-2,5-dione and nitrous acid?
As you may know from diazotisation reactions, $\ce{HNO2}$ is a generator of the nitrosonium cation, $\ce{NO+}$. Electrophiles like these can react with the enol tautomer of hexanedione:
Following ...
- 71.9k
20
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Does folic acid contain a benzyl or a phenyl group?
Does folic acid contain a benzyl or a phenyl group?
This is the question asked in the title. At the first glance to the structure, one would say folic acid consists of phenyl function but not benzyl ...
- 42.1k
17
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Which carbons in pyrrole have the highest electron density?
Interesting question, more subtle than I realized!
Theoretical approach: I would turn to resonance and induction as the rationale for electronic properties. I think all of your resonance forms may ...
- 2,244
15
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What is the mechanism of the reaction between hexane-2,5-dione and nitrous acid?
Orthocresol did a great job describing how to get to the isoxazole methyl ketone. However, nitrous acid can be an oxidant. The methyl ketone in the presence of mineral acid, which you need to get the ...
- 17.5k
14
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Which carbons in pyrrole have the highest electron density?
That is really not a fair question and even with a computational approach the differences are more or less marginal. The approach by electron pusher is certainly the way to go, and here is the ...
- 44.4k
14
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Reaction of substituted furan with methyl vinyl ketone with subsequent rearomatisation
Your Diels–Alder adduct is pretty much correct. Without any further evidence we cannot definitely say whether the exo or the endo adduct is formed (you have drawn the exo adduct, which generally ...
- 71.9k
14
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What is the mechanism of azulene synthesis?
The @orthocresol link to the Zincke reaction is a good start to the mechanism. You are correct about the first step. Dimethylamine adds to the electrophilic pyridinium salt 1 as illustrated in 1 $\...
- 17.5k
13
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How to check for geometrical isomerism in cyclic compounds?
I hope the statutes of limitation haven't run out. Structure 1 is a (Z)-alkene. Using Cahn-Ingold-Prelog (CIP) protocol, the rings are deconstructed as shown in diagram 2. The larger red arrow marks ...
- 17.5k
13
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Are nucleophilic aromatic substitutions stepwise or concerted?
TL;DR Most SNAr reactions proceed via concerted mechanisms without a discrete anionic intermediate. This is typically the case when there is a good leaving group (e.g. chloride or bromide) and if the ...
- 71.9k
12
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Regioselectivity in Electrophilic Aromatic Substitution of Pyrrole and Indole
The traditional explanation for the reactivity of indole at C–3 is that attack at C–3 does not disrupt the aromaticity of the benzene ring in the cationic intermediate (see any organic chemistry book; ...
- 71.9k
12
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What's special about the purine scaffold?
It is important to remember that the purine scaffold is one of the most fundamental organic structures in all lifeforms. From an evolutionary standpoint, this means that there must have been a simple, ...
- 2,010
10
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What's the mechanism of the reaction of (E)-methyl 3-(furan-2-yl)acrylate in acidic methanol?
Unfortunately I cannot agree with the currently accepted answer. This 1,5-hydride shift that was invoked seems to have a very strained transition state (the cyclic, planar system means that the "1" ...
- 71.9k
10
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Pyridine synthesis by tin(II) chloride reduction of 5-nitronorbornene
This reaction was conducted by Ho and Liao1. Nitro compound 1 is reduced to the nitroso compound 2 which undergoes a [3+3] electrocyclization to form 3 (4). Tautomerization of 4 to 5 is followed by a ...
- 17.5k
9
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What is the reaction mechanism between acetophenone and ethyl phenylpropiolate to form a 2-pyrone?
The general idea in the answer above is correct, but some of the details need to be looked at more closely.
The first step is as drawn in the original post. Deprotonation of the ketone, followed by ...
- 71.9k
9
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Acidity of metronidazole
There are no acidic groups in metronidazole. The $\mathrm{p}K_\mathrm{a}$ you are quoting relates to the protonated form of the molecule (usually hydrochloride or benzoate). The most easily removed ...
- 23k
8
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Is cyanidin aromatic?
No doubt it is aromatic.
The $4n+2$ rule is intended for a single cycle of π-electrons, which may possibly include multiple rings but can't have any interior atoms or pendant π- bonds (which would ...
- 62.6k
8
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Is this sydnone aromatic?
One of Paul Schleyer's students, Matthew Duvall, has studied the aromaticity (or lack thereof) of mesoionic compounds, such as sydnones and münchnones, using various techniques.[1] In his thesis, ...
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8
votes
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Is the term "heteroatom" reserved for exclusive elements?
The IUPAC Goldbook provides no 'official' definition of the term heteroatom,and as such you're somewhat free to use (and abuse) the term as you see fit.
Since no IUPAC definition exists, it may be ...
- 17.2k
8
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Why do dithiins have 8 π-electrons?
TL;DR Ab initio HF molecular orbital studies of the potentially antiaromatic $8\pi$-electron systems of distorted and planar 6-membered rings revealed that conformational rigidity (calculated or ...
- 38.5k
8
votes
Why are carbons of Inositol chiral centers?
Consider 2,3-butanediol.
This compound has 2 stereocenters. The meso version of this compound is achiral. However, there are still two stereo centers. As drawn, the left one is (R) and the right one ...
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8
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Comprehensive Functional-Group-Priority Table for IUPAC Nomenclature
Blue book would be indeed the reference to go to. Chemistry.se's page resources for learning chemistry though includes a contribution about nomenclature in general, including the freely accessible ...
- 31.4k
7
votes
Side chain hydroxylation of pyrrole
I'd like to propose a dark, non-radical pathway :)
Pyrroles, supposed that they are not fully substituted, undergo electrophilic aromatic substitutions with halogens.
For the given starting compound,...
- 44.2k
7
votes
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Comparing basicity of imidazole and 2-imidazoline
I was unable to find experimental $\mathrm{p}K_\mathrm{a}$ values of imidazoline. However, the tools one can use to calculate and thereby predict $\mathrm{p}K_\mathrm{a}$ values are pretty good ...
- 68.7k
7
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How to tell whether lone pairs in heterocycles contribute to aromaticity?
For the most common situations use this rule: a conjugated ring atom needs either a ligand or a localized electron pair to replace a missing ligand. Any remaining electron pairs are then part of the ...
- 62.6k
7
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Why does nucleophilic aromatic substitution occur at C-2 and C-4 of pyridine?
Nucleophilic aromatic substitution on pyridines (or related heterocycles such as quinolines or pyrimidines) regioselectively occurs at the 2- and 4- positions. These can be thought of as being "ortho" ...
- 71.9k
7
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Why is aniline more basic than pyrrole?
There would be no aromaticity in pyrrole after protonation since there is no lone pair to allow for Hückel's rule for aromaticity (the $4n+2$ rule). So, upon protonation, you are destroying ...
- 7,050
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What molecule is pictured on the cover of Dead Sara's album "Ain't It Tragic?"
I see two possible candidates: buprenorphine and thienorphine.
Both are strong opioid painkillers fitting the “art” theme.
Depending on how one draws the location of what appears to be a methoxy and a ...
- 38.5k
7
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Stability of hexazine
How can it be so much unstable when it's structure resembles so much to that of benzene which is exceptionally stable.
Benzene is not exceptionally stable to start with. As you substitute more and ...
- 42.3k
6
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What would be the mechanism for this condensation reaction?
Your 2-methyl-1,3-benzoxazole is a masked acetic acid.
Remember that one way to synthesize oxazoles actually starts from aldehydes (and uses TosMIC).
So, yes, the reaction is an aldol condensation ...
- 44.2k
6
votes
Removal of oxygen from pyridine N-oxide
I'm not sure whether $\ce{PCl3}$ can lead to the installation of a chlorine atom at C-2. I performed a cursory Reaxys search and in the first page saw several examples of deoxygenation without ...
- 71.9k
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