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Please tell if the 2 given conpound are Anti-aromatic or Non-aromatic, enter image description here

I have confusions arising due to incosistent facts all around internet some of them are as follow :

1.) Arguments for Cyclopropenyl Anion

a.) Wikipedia which under the heading of "Effects on reactivity" clearly states that :

"However, the cyclopropenyl anion has 4 π electrons in a cyclic system and in fact has a substantially higher pKa than 1-propene because it is antiaromatic and thus destabilized"

b.) This Answer on ChemSE which clearly states that its Non-Aromatic in Nature

c.) Also this NEPTL site which clearly states that:

Cyclopropene is not aromatic because one of its ring atoms is sp3 hybridized so it does not fulfill the criterion for aromaticity. But the cyclopropenyl cation is aromatic because it has an uninterrupted ring of p-orbital and (4n+2) π-system. The cyclopropenyl anion is antiaromatic as it has (4n) π-system.

2.) Arguments for cycloheptatrienyl anion

a.) This Question on ChemSE where the same question have 2 deflecting answer this answer is saying is that the anoin is antiaromatic and this states that the anion is nonaromatic

b.) Also my book (solomons and fryhle organic chemistry adapted for JEE) gives this as Antiaromatic

I don't know which one is correct, please help by providing a comprehensive answer with a reason that can be applied everywhere in such questions.

EDIT: Hello the one who closed the question can I ask the reason for closing as much I can do I abid by this guideline I asked my question straigthformward and then presented my research please tell me why my question is put on hold, I seek answers

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    $\begingroup$ Basically the SE answer you mention should fiv your current Q as well. Given the existance of a species that results in antiaromaticuty, then ist that the species avoid it. The key is that antiaromaticity is forced, it serves to determine if a formally conjugated system does indeed undergo delocalosation, not to establish its existence. $\endgroup$
    – Alchimista
    Feb 24, 2019 at 13:44
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    $\begingroup$ Well, in the past antiaromaticity was attributed to about as many structures as aromaticity, thing is it pretty much doesn't work at all. $\endgroup$
    – Mithoron
    Feb 24, 2019 at 18:53
  • $\begingroup$ chemistry.stackexchange.com/questions/45040/… $\endgroup$
    – Mithoron
    Feb 24, 2019 at 19:05
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    $\begingroup$ It would be better to just make a post about when antiaromaticity actually applies, but as you noticed, you could get pretty much any answer, ranging from not applying to anything to everything one might suspect. BTW it's technically a follow-up of two old posts, but such question shouldn't just repeat old question. $\endgroup$
    – Mithoron
    Feb 25, 2019 at 2:20
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    $\begingroup$ Both of them are antiaromatic as both of them has 4n π electrons.Also,I'm going to suggest you that if have to choose between internet and books,you should choose books as reference because there are a lot of people on the internet who might not know everything but nonetheless they post about that topic i.e. there's no one to verify all the stuff on the internet but the books are genuine. $\endgroup$
    – Abner Alfred Thompson
    Feb 25, 2019 at 3:14

1 Answer 1

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Whenever you want a definition of a chemical concept, you should refer to the IUPAC's Gold Book which in this case states that antiaromatic compounds are

compounds that contain 4 n(n ≠ 0) π-electrons in a cyclic planar, or nearly planar, system of alternating single and double bonds, e.g. cyclobuta-1,3-diene.

A corollary to this rule is that all the atoms must have an sp2-hybridization, so the orbitals can overlap. However, the carbon bearing the negative charge has an sp3-hybridization, i.e. they does not count as π-electrons but σ-electrons and that breaks the rule of alternating single and double bonds. So both anions are non-aromatic.

Edited after the OP opened my eyes on a big mistake I had made in answering his question. Sorry about that.

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  • $\begingroup$ as i know that alternating single and double bond means conjugation but as chemistry.stackexchange.com/a/51470/73826 this answer suggest the carbanion moves out of plane and hence can't remain in conjugation ......please clear this in the answer $\endgroup$
    – Advil Sell
    Feb 24, 2019 at 13:41
  • $\begingroup$ I dont know if I am wrong that some ring with a -ve charge are aromatic in which the electrons are considered as $\pi$ electron and thus the congugation is present , can you explain why they aren't considered as $\pi$ electrons here ??? $\endgroup$
    – Advil Sell
    Feb 24, 2019 at 14:17
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    $\begingroup$ Oh right, I get it. You actually wonder why the cyclopentadienyl anion is aromatic, and the anion center is sp2 in that case, whereas it is not in the case with cycloheptadienyl anion. Well hybridization occurs only if it helps getting a lower potential energy or, in other terms, if there is an incentive to do so. There is an incentive to change hybridization to go aromatic, but not to go antiaromatic. $\endgroup$
    – SteffX
    Feb 24, 2019 at 14:30
  • $\begingroup$ oh...Nice I think I got your point thanks for the answer $\endgroup$
    – Advil Sell
    Feb 24, 2019 at 15:42

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