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Questions tagged [heterocyclic-compounds]

For questions concerning compounds possessing rings with two or more different types of atoms.

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Are nucleophilic aromatic substitutions stepwise or concerted?

Recently, there has been a lot of discussion about nucleophilic aromatic substitution (SNAr) reactions apparently being concerted instead of stepwise (e.g. Krämer, K. Textbook aromatic substitution ...
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1answer
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Why does nucleophilic aromatic substitution occur at C-2 and C-4 of pyridine?

In the following reaction of 2,3,4-tribromopyridine with sodium methoxide in methanol,[1] why are only the C-2 and C-4 bromines replaced with methoxy groups? Why doesn't the bromine at C-3 also get ...
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1answer
176 views

Aromaticity of heterocyclic compound [closed]

This is a question of JAM 2017. According to the answer key the answer is 4. But I found only the last 3 as aromatic . So which one is the 4th aromatic compound? Please explain
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Are crown ethers “recycled”, typically?

I know that crown ethers have the interesting property of strongly complexing alkali metals, which allows them to be used in organic solvents (eg. as "dissolving-activity enhancing agents" for ...
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Why does 2-pyridone with chlorine gives 3,5-dichloro-2-pyridone?

Why does 2-pyridone react with chlorine to give 3,5-dichloro-2-pyridone? I thought that 2-pyridone is resistant and will yield only 5-chloro-2-pyridone or even a combination with 3-chloro-2-pyridone
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Mechanism of heterocyclic ring formation

I saw a question here about the mechanism for a heterocyclic ring formation: What is a reasonable mechanism for the following reaction?. I tried solving the mechanism but I am missing something. Let ...
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1answer
117 views

IUPAC of heterocyclic compounds terminology

During my studies of heterocyclic compounds I learned that monocyclic compounds has prefix+ stem+ suffix. the prefix is coming from the heteromolecule name (e.g oxgen --> oxa- ) however the stem and ...
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What is SO2Ar as a functional group and how is it relevant in this reaction? [closed]

This reaction came up in one of my problem sessions and I had never seen an SO2Ar function group before. What are it's general properties and how is it relevant to this reaction? Any help is greatly ...
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What is a reasonable mechanism for the following reaction?

Hello all! I'm stuck on this one question and am not sure how to finish the mechanism. What I did was attack the alkyne first with the N farthest to the left. I'm not sure what do to after that though....
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1answer
74 views

Heterocyclic Compounds - Glucose

Why cyclic glucose is not a heterocyclic compounds if it consist Oxygen as a Heteroatom ?
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264 views

How to tell whether lone pairs in heterocycles contribute to aromaticity? [duplicate]

How can I decide whether lone pair electrons take part in the continuous overlap of electron or not? For example, the lone pair in pyridine is not a part of the conjugated system, whereas the lone ...
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2answers
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What are the IUPAC names for singly- and doubly-protonated piperazine?

If ammonia, $\ce{NH3}$, is protonated, it becomes ammonium: $\ce{NH4+}$. If piperidine is protonated, it becomes piperidinium: If piperazine is protonated once, what does it become? By analogy, I ...
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One-pot synthesis of pyrazole [closed]

I am trying to follow a published paper. It is a one-pot synthesis of pyrazole from a ketone and and acid chloride via a diketone intermediate. Here is the produre from the paper: General Procedure:...
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1answer
252 views

Why is the rate of nitration greater for thiophene than toluene?

Toluene has a $\ce{CH3}$ group attached to the benzene ring and as a result due to the +I effect of $\ce{CH3}$, the electron density in the ring increases and it undergoes nitration faster than a ...
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1answer
165 views

Directionality of ring current-induced magnetic fields in purines

What would be the directions of ring current-induced magnetic fields in purine-like heterocycles in a ​strong magnetic field? Would be the antiparallel state be a default state for these substances in ...
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2k views

What is the mechanism of the reaction between hexane-2,5-dione and nitrous acid?

I don't understand the mechanism of the first reaction; I tried different ways but I can usually find how to make the ring without the double bonds, but it's obviously not the right thing; I think ...
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Understanding smoke chemistry of tobacco and/or marijuana

In an effort to understand the effects of tobacco vs marijuana smoke on health, the chemistry of smoking plants, and remembering some of the chemistry I took in college, I came across a 2007 study ...
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1answer
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Separation of alkylated 1,2,4-triazole in solution

I was looking into heterocyclic compounds and their alkylation (i.e. the regioselectivity of the alkylation of the compound). People are able to give pretty exact numbers, for an experiment done in ...
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1answer
425 views

How can nucleophilic substitution happen at the sp²-hybridised carbon of 4-chloropyridine?

Why can substitution of the C–Cl bond occur at the sp2-hybridized carbon in the following reaction (taken from Clayden et al., Organic Chemistry (2nd ed.), p 700)? Ordinarily, SN1- and SN2-type ...
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1answer
532 views

pKa of imidazoles

I was looking for the $\mathrm{p}K_\mathrm{a}$ of imidazole and found this $\mathrm{p}K_\mathrm{a}$ table [1]: \begin{array}{ll} \text{Compound} &\mathrm{p}K_\mathrm{a} \\ \hline \text{...
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1answer
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Nucleophilic aromatic substitution on pyrimidines: C2 vs C4 selectivity

[There are many similar questions on Chemistry.SE (e.g. 1, 2) and a quick search will reveal all of them, but nothing on this in particular.] The reaction of 2,4-halopyrimidines with nucleophiles ...
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2answers
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Why do dithiins have 8 π-electrons?

It is mentioned on Wikipedia that dithiins have 8 π-electrons. Why is this so? I was thinking it would suffice for just one of the lone pairs on one of the sulfur atoms to participate in resonance ...
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Separation of Regioselectively Alkylated Ionic Solid

How would one go about separating a solid mixture of regioselectively alkylated solids. I'll give a specific example. Take the hypothetical alkylation of methylpentazole with MeI. There are three (...
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1answer
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Ring opening of aziridinylmethyl and oxiranylmethyl radicals

When a radical is alpha to a three-membered ring, it is common for the ring to open via β-scission (to relieve ring strain): When the ring contains a heteroatom there are a couple of different ...
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Is the middle ring of this organic compound aromatic?

Is the middle ring with 5 atoms of (4⁠Z)-4-[(4-methoxyphenyl)methylidene]-5-methyl-2-phenyl-2,4-dihydro-3⁠H-pyrazol-3-one aromatic? The carbonyl group could become a negatively charged oxygen, the ...
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1answer
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Why is the 2-position of pyridine electron richer than the 4 position

I am wondering about the electronic structure of pyridine. If we look at nucleophilic substitution, which favored on electron poor centers, for 2-chloro and 4-chloro pyridine we see that the ...
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3answers
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Comparing basicity of imidazole and 2-imidazoline

I recently sat for an exam in which I was asked to compare the basicity of the above compounds. I thought imidazole would be more basic because it is aromatic but according to the answer key 2-...
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1answer
426 views

Which rings of this heterocyclic compound are aromatic?

I am wondering which of the inner two rings of this compound are aromatic? I know the rules for aromaticity. But this case is difficult for me. Regarding the smaller ring, I guess the sulfur ...
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2answers
436 views

Is the conjugate base of pyrrole resonance stabilised?

This is something I am conceptually struggling with, if I deprotonate pyrrole on the nitrogen in the ring, is it true that the conjugate base is not resonance stabilised, because the orbital is ...
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1answer
281 views

Why is 2-pyridone so much more acidic than a regular amide?

I am comparing the structures of 2-pyridone and a regular (cyclic) amide-what is the main factor contributing to the increased acidity of 2-pyridone compared to a normal amide. For pyridone, I thought ...
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2answers
656 views

Is the term “heteroatom” reserved for exclusive elements?

From my experience, typically in organic chemistry, the implication of "hetero-atom" in some molecule is understood as B, N, O, S, P or a halogen -- or any nonmetallic element, perhaps. If one ...
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Reaction of substituted furan with methyl vinyl ketone

I recently came across this organic chemistry problem. I just observed that the order of substituents on the product is same as that on furan. I know furan undergoes Diels-Alder reaction and so I ...
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236 views

Reaction of 3-Chloropyridine

I've given a question , 3-chloropyridine + NaNH2 gives out A . Compound A on further reaction with furan gives compound B. What I think now , First step is simple elimination addition reaction . So ...
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1answer
387 views

Reaction of coumarin with phenylmagnesium bromide

I came across this problem.. I thought that the Grignard reagent, PhMgBr, would cleave the lactone and then subsequently add to the ketone formed, giving an allylic tertiary alcohol after aqueous ...
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1answer
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Is cyanidin aromatic?

The structure of cyanidin is as follows: There are eight double bonds in the entire compound, and hence $8 \times 2 = 16$ π-electrons, which does not satisfy the $4n + 2$ rule. However, the molecule ...
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1answer
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Regioselectivity in Friedel–Crafts acylation of thiophene

In the above reaction, I understand that $\ce{AlCl3}$ is acting as a Lewis acid to generate an acylium ion, which is a strong electrophile. Would this electrophile attack at carbon 2 or 3? I think ...
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1answer
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Hybridization of heteroatom

Why is the hybridization of oxygen in the seven membered ring pictured below $sp^3$, while the oxygen has a hybridization of $sp^2$ in the 5 membered ring? This also may be an error in the answer key ...
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557 views

Reaction of potassium cyanide with 2-(chloromethyl)furan

What would the mechanism for the reaction between 2-(chloromethyl)furan and potassium cyanide be, as detailed below? I know that for 6-membered rings like pyridine, a $\mathrm{S_NAr}$ reaction can ...
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3answers
203 views

Mechanism for Amino-Imidazole Ring Fission

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 ...
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How many stereoisomers of octahydroquinoline are there?

I am trying to work out how many stereoisomers there could be of the following... As indicated, I think there are two sites of varying the stereochemistry. The top site can have the hydrogen in ...
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1answer
755 views

Mechanism for the synthesis of 2-pyridone from pyridine N-oxide

I'm specifically interested in the pathway from pyridine N-oxide, where there is some kind of reaction and rearrangement with acetic anhydride. I'm assuming there is first a substitution (by the ...
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1answer
195 views

What happens when pyridine N-oxide reacts with dichlorocarbene?

It seems that the combination of sodium methoxide (a base) and chloroform will generate dichlorocarbene, $\ce{CCl2}$, by α-elimination. What happens after that, though? It is an ortho formylation ...
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1answer
179 views

Regioselectivity of an amination reaction of 2,6-dichloro-3-nitropyridine

In the formation of ethyl 4-(6-chloro-3-nitropyridin-2-yl)piperazine-1-carboxylate G, why is the substitution favoured at the 2-position? I would have said that the 6-position substitution is ...
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1answer
87 views

Regioselectivity in the formation of an imidazo[1,2-a]pyrimidine

In the heterocycle synthesis below (taken from Org. Process Res. Dev. 2006, 10 (3), 398–402), a 5,6-fused heterocycle (an imidazo[1,2-a]pyrimidine) is formed by treating 2-amino-4-(trifluoromethyl)...
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Which carbon in pyrrole has the highest electron density?

In pyrrole, which carbon atoms have the most electorn density I know that the electron density will be maximum on that carbon in which there is a maximum mesomeric or resonance effect. Here the ...
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2answers
259 views

Numbering in phenolphthalein versus ascorbic acid

According to Wikipedia, the recommended IUPAC name for phenolphthalein is 3,3-bis(4-hydroxyphenyl)-2-benzofuran-1(3⁠H)-one, and for ascorbic acid is (5⁠R)-5-[(1⁠S)-1,2-dihydroxyethyl]-3,4-...
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2answers
461 views

What would be the mechanism for this condensation reaction?

Below is the reaction in question. Will it go like an aldol consensation would, where the base would deprotonate the methyl group of the benzoxazole moiety, the negative charge would be transferred ...
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2answers
278 views

Side chain hydroxylation of pyrrole

What reagents are required to form 1-[1,5-dimethyl-3-phenyl-4-(propan-2-yl)-1⁠H-pyrrol-2-yl]propan-1-ol with 1,2-dimethyl-4-phenyl-3-(propan-2-yl)-5-propyl-1⁠H-pyrrole as starting material? Is it ...
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1answer
72 views

Reaction of 2-ethyl-5-methyl-3-phenylfuran under acidic conditions

I was asked: Does protonation occur to the electronegative oxygen? What is the function of the heat? I think that there will be protonation at C-3 which will break the aromaticity and the ...
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1answer
992 views

Multiplet shape in proton NMR of morpholines

I recently carried out a Buchwald–Hartwig reaction to attach a morpholin-4-yl group to an aromatic ring: In the proton NMR of the (columned) product, I found the peaks corresponding to the morpholine ...