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Which of the following ions(A and B respectively) is more stable? How can we explain this on the basis of resonance?

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Here's what the solution said:

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Structure (A) is a primary carbocation and has no hyperconjugative stability while (B) is a secondary carbocation having 2 alpha Hydrogens which indicated that (B) must be more stable. But when I looked at the given solution to the problem, I was a bit confused.

I don't get why there is no resonance possible in (B), aren't they basically the different resonance structures of the same intermediate?
I looked for something like this on the web, and it showed similar results saying (B) isn't planar and hence doesn't have resonance while (A) does, so (A) is more stable.

Obviously, if B wasn't planar then it wouldn't have any resonance but why isn't it planar? Is this about the chair conformation of cyclohexane?

I'm not able to understand these points and would appreciate if someone could help me understand this.

Prajwal Tiwari
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  • according to JEE level, I agree with your thought process, I think hyper-conjugation is the right way to decide, chair conformation is generally not a part of JEE Syllabus, at least, not till this extent. We generally assume it to be planar. – Soumil Gupta Sep 25 '21 at 02:24
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    They: I and II; you: A and B. Where is structure II – Karsten Sep 25 '21 at 03:36
  • Beside hyperconjugation, which is certainly at play here, be careful with the words used. At the root you can't evaluate stability of one limiting form by use of resonance. It is somehow a contradiction in terms. Pedantic: in the above, the limiting form is a hybrid itself,if hyperconjugation is involved. Of course practically no need to sketch it. But I think you get what I mean. – Alchimista Sep 25 '21 at 06:16
  • @KarstenTheis (A)->(I) , (B)->(II) they basically named the structures A and B in the question but started referring to them as (I) and (II) in the solution :/ – Prajwal Tiwari Sep 25 '21 at 17:30
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    No they did not. Carefully read the question and answer key again. – Karsten Sep 25 '21 at 18:41
  • @PrajwalTiwari about A B I & II: is indeed the pedantic point I've referred to! So I wasn't too pedantic – Alchimista Sep 26 '21 at 06:48
  • @KarstenTheis Oh yes I'm really sorry, I mistakenly cropped out that part from the question image, I have edited the question and added the details of A and B in the question statement. Really sorry for the confusion – Prajwal Tiwari Sep 27 '21 at 02:25

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