Questions tagged [heterocyclic-compounds]

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

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Why electrophilic attack at thiazole takes place at C-5? [closed]

Why electrophilic attack at thiazole takes place at C-5 instead of C-4. Generally electrophilic attack at azoles take place at C-4.
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1answer
66 views

Proton NMR splitting in 2-substituted furan

I have recently run proton NMR on 1-(furan-2-yl)ethan-1-ol I synthesised in the lab. My 400 MHz spectrum consists of the following peaks: 7.36 ppm (dd, J = 1.9, 0.9 Hz, 1H) 6.31 ppm (dd, J = 3.3, 1....
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52 views

Fischer indole synthesis: significance of choice of acid catalyst

Lately, as a matter of interest, I have been studying sigmatropic rearrangements. I came across the Fischer indole synthesis, whose Wikipedia article states: The Fischer indole synthesis is a ...
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53 views

Type of chirality in polycyclic compounds

Ignoring whether or not this molecule could exist, is there a name for this type of chirality? This molecule's mirror image cannot be superimposed on itself but there are no chiral centres. Even ...
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1answer
212 views

Pyridine: Protic or Aprotic

I know pyridine is a polar aprotic solvent (owing to a permamnent dipole generated), but if acidified it forms pyridinium cation. So, does it then function as polar protic solvent?
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108 views

Why is aniline more basic than pyrrole?

In a question asking to compare the basicity of pyrrole and aniline, the explanation given for aniline being more basic than pyrrole was as follows: Basicity depends on the availability of lone pair ...
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1answer
73 views

Why does magnesium bromide transfers from a carbon atom to nitrogen in piperidine?

In this reaction, why does $\ce{MgBr}$ goes to the $\ce{>NH}$ group and form a bond with nitrogen by removing $\ce{-H}$. Also where does the negative charge go?
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1answer
53 views

Acidity of thiamine - how comes hydroxide anion with pK about 15 ionizes thiamine with pK about 18?

Textbooks say removing proton from thiamine's C atom will produce a resonance stabilized carbanion which is hence bioactive. That's OK, but how comes that 1) we abstract the acidic proton with the OH ...
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1answer
158 views

Pyridine synthesis by tin(II) chloride reduction of 5-nitronorbornene

What is the reaction mechanism here? I guess the $\ce{SnCl2}$ reduces $\ce{NO2}$ to $\ce{NH2}$ but then what happens?
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1answer
351 views

Regioselectivity in Electrophilic Aromatic Substitution of Pyrrole and Indole

If we look into the structures of Pyrrole and Indole, they are very similar. Only Indole has one extra Benzene ring attached to it, i.e. if we attach one Benzene ring to Pyrrole, what we'll have is ...
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68 views

Stubborn CuAAC reaction as derivatization for ESI-MS

Problem description I have a substance that is extremely non-polar and therefore does not ionize in the ESI source, which makes it impossible to quantify small amounts. The substance contains only two ...
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1answer
68 views

Friedel-Crafts acylation of furan [closed]

Can furan undergo Friedel–Crafts acylation with benzoyl chloride? Some people say it will have no reaction. Is it true? If so, why cannot it undergo Friedel–Crafts acylation like other ketones?
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Can Diels-Alder reaction occur using reagents of Robinson annulation?

Robinson annulation seemed somewhat like the Diels-Alder reaction to me, if all ketonic groups were to be represented as enol then cyclohexanone would be like diene and the Michael acceptor as a ...
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Metalation of thiophene

So lately I've been studying the concerted metalation-deprotonation of thiophene and I came to the conclusion that the alpha positions of thiophene are the most reactive, which is why one of those ...
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96 views

Reaction of diamines with carboxylic acids to form imidazole

I've recently came across this reaction and my guess is that firstly an amide forms that later reacts with the second amine group. Is this a general reaction? Does it matter if the compounds used are ...
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127 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
164 views

Name of “the” benzodiazepine

Wikipedia has a thorough article on the benzodiazepines. Of course, it is written primarly from the pharmacological point of view; but there is also the "Chemistry" section, which includes the IUPAC ...
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1answer
152 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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146 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
359 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
82 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
960 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
680 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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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
115 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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284 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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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
2k 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
470 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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95 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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191 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
847 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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356 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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298 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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181 views

Heterocyclic Compounds - Glucose

Why cyclic glucose is not a heterocyclic compounds if it consist Oxygen as a Heteroatom ?
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729 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
362 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
130 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
1k 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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253 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
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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
93 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
1k 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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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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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
344 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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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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238 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 ...