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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
4
votes
1answer
386 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 ...
17
votes
1answer
197 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 ...
6
votes
2answers
260 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 ...
9
votes
1answer
185 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 ...
11
votes
1answer
200 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 ...
4
votes
1answer
3k views

How is purine aromatic?

If we count the total number of π electrons, there are 10. But to apply Hückel's rule to this molecule, we should count only the electrons of the outer periphery and there are 8 of these. How can the ...
6
votes
1answer
411 views

Is a pyrylium ring aromatic?

I am trying to figure out which rings in callistephin are aromatic: I know that the benzene rings definitely are aromatic, but I'm not sure about the ring with the positively charged oxygen (...
17
votes
2answers
1k views

Is this sydnone aromatic?

Is the following molecule aromatic? It does seem like it will be aromatic because it is similar to furan. I am confused because of the positive charge on the $\ce{N}$.
9
votes
3answers
4k views

When do lone pairs on nitrogen contribute to aromaticity?

I've been told that 1,2,4-trimethyl-1⁠H-imidazole is aromatic. As it has four obvious pi electrons (in the double bonds), I assumed that it was anti-aromatic as opposed to aromatic. I've been ...
5
votes
2answers
8k views

Why is only one lone pair in imidazole delocalised?

I was wondering why only one of the nitrogen lone pairs in imidazole is involved in the delocalized π-system. Specifically, I was wondering why it is that lone pair B in particular is delocalized, ...
4
votes
2answers
711 views

Why isn’t azete aromatic?

I’m confused, because it seems like Hückel’s rule is satisfied (two electrons from the nitrogen lone pair and four from the double bonds) and that the molecule should be aromatic. Where am I going ...
5
votes
1answer
958 views

Do lone pairs contribute towards the pi electron count of heterocycles?

I'm not able to understand how the following compounds are aromatic. When should the lone pairs on heteroatoms be taken into consideration when counting the number of π electrons?