Comments on: Carbocation Rearrangement Reactions (2) – Alkyl Shifts

By: Aadya

Aadya — Thu, 26 Mar 2026 05:42:36 +0000

Angle strain…. i think

By: James Ashenhurst

James Ashenhurst — Sat, 21 Feb 2026 09:32:09 +0000

In reply to A James. There is really no driving force for ring opening. If it is going from a secondary carbocation to a tertiary carbocation in doing the ring expansion, then there would be a driving force, but the ring expansion going from 5- to 6- does not provide one.

By: A James

A James — Sat, 21 Feb 2026 08:23:31 +0000

In an electrophilic addition reaction , say there is a carbocation which is on a 5 membered ring. It is in a position to expand to 6 membered, but on doing so its stability (via hyperconjugation) decreases. What product should we mark as major in that case?

By: James Ashenhurst

James Ashenhurst — Sun, 24 Nov 2024 13:30:43 +0000

In reply to Aadity. Hydride shifts are faster.

By: Aadity

Aadity — Sat, 23 Nov 2024 04:19:16 +0000

Thanks for the post!
If in a situation both alkyl and hydride shifts can lead to more stable carbocations (example: secondary carbocation adjacent to tertiary and quaternary carbon) which one will give the major product(s) ?

By: Soham Saha

Soham Saha — Mon, 27 May 2024 07:06:45 +0000

Thanks for this wonderful website. I am not able to go for the membership plan, but all the information you’ve laid out for free is staggering and truly wonderful. I have learnt (and am learning) a lot from here.

I have a question too. If we take this molecule (https://www.wolframalpha.com/input?i=smiles+identifier+C1C%28%5BC%2B%5D%28C%29%28C%29%29C1), will it do ring expansion? Or will sigma-resonance stabilize it enough?

By: James Ashenhurst

James Ashenhurst — Mon, 18 Mar 2024 17:41:55 +0000

In reply to Pratistha Bhattacharjee.

In real life, both can occur.

In an exam-type situation, if you are faced with expanding a 4-membered ring to a 5-membered ring *or* doing a methyl shift to give a tertiary carbocation, you should expand out the 4-membered ring due to relief of ring strain.

There is very little relief of ring strain on going from 5- to 6-, and for that reason the two possibilities are a lot less clear cut in that case.

By: Pratistha Bhattacharjee

Pratistha Bhattacharjee — Thu, 07 Mar 2024 07:13:01 +0000

If there are possibilities of both tertiary carbonation and ring expansion then which one gets more preference?…which one forms?

By: James Ashenhurst

James Ashenhurst — Sat, 24 Feb 2024 18:30:48 +0000

In reply to CHANDRU. Almost certainly the hydride would migrate preferentially. It's just easier from a principle of least motion standpoint.

By: CHANDRU

CHANDRU — Sat, 24 Feb 2024 13:51:47 +0000

hi James if there were possibilities to form a tertiary carbocation in two ways in one way it’s an alkyl shift and another is a hydride shift, both leading to a stable carbocation (tertiary) which is likelyto occur …?