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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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41 views

Confusion with IUPAC naming of Morphine

I'm having trouble understand what sections of the molecule morphine relate to what sections of its corresponding IUPAC name of (4R,4aR,7S,7aR,12bS)-3-methyl-2,4,4a,7,7a,13-hexahydro-1H-4,12-...
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1answer
69 views

Why does coumarin predominantly exist in keto form?

By applying the logic that phenol exists in enol form rather than keto form as it attains aromatic character, why is it not the case in coumarin?
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24 views

Favoured position in nitration of pyrrole [duplicate]

I try to figure out the preferred position of nitration (determine whether compound A or B is the major product) by looking at the resonance structures of the intermediate cation. The solution then ...
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2answers
250 views

What is the IUPAC preferred name of this tetracyclic natural product?

On page 819 of Vollhardt, Organic Chemistry 7th Ed., the following "subunit of the antibacterial platensimycin" appears. I have attempted to apply von Baeyer and skeletal replacement ('a') ...
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1answer
77 views

What is wrong in this reaction? [closed]

What is wrong in this reaction? I cannot find anything wrong, please help. Any hints would be appreciated.
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3answers
335 views

Why are carbons of Inositol chiral centers?

I was asked to draw all possible stereoisomers of inositol (1,2,3,4,5,6-cyclohexanehexol). To obtain the answer I had to assume that all six carbons of the molecule are asymmetric, which (bearing in ...
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1answer
349 views

What is the mechanism of azulene synthesis?

In the Organic Syntheses preparation of azulene (http://www.orgsyn.org/demo.aspx?prep=CV7P0015) there are two reactions. First is a clevage of the C-N bond in pyridine and the second one is the ...
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50 views

Exceptionally weak basicity of pyridine [duplicate]

It is often explained that the relatively lower basicity of pyridine, relative to most amines, is due to the fact that the $\ce {N}$ lone pair resides in an $\ce {sp^2}$ hybridised orbital, instead of ...
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2answers
100 views

How do dibromopyrazolones undergo base-promoted decomposition?

I was not sure but seeing the base as NaOH I used the fact that it will take most acidic hydrogen that is N-H and electron pair will come over it and it will resonate from two sides. I could make upto ...
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1answer
161 views

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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210 views

Reaction between Salicylaldehyde and 2-Benzoylpyridine

In a paper by Sheng et al (10.1016/j.dyepig.2018.07.036) the authors synthesize the compound MZC as shown in the scheme below. I'm looking for information about what the reaction mechanism is that ...
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1answer
547 views

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
366 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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1answer
104 views

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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90 views

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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150 views

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
573 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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1answer
185 views

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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190 views

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
137 views

Heterocyclic Compounds - Glucose

Why cyclic glucose is not a heterocyclic compounds if it consist Oxygen as a Heteroatom ?
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1answer
435 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
282 views

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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1answer
109 views

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
718 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
206 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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2answers
3k 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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1answer
3k views

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
82 views

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
729 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
836 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
587 views

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
282 views

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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76 views

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
183 views

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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1answer
186 views

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
2k views

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
3k views

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
496 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
660 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
495 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
903 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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1answer
530 views

Reaction of substituted furan with methyl vinyl ketone with subsequent rearomatisation

I am supposed to provide a mechanism for the above transformation. I observed that the order of substituents on the product is same as that on furan, and since furan undergoes Diels–Alder reactions, I ...
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0answers
532 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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2answers
619 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
206 views

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
2k views

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
738 views

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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2answers
735 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
236 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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0answers
114 views

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 ...