3
$\begingroup$

Why do vinylic carbocations generally not undergo hydride rearrangement from neighbouring sp3 carbon to get more stability?

According to me, a rearrangement would lead to an allylic carbocation, which is more stable than vinylic, hence the rearrangement should be favorable.

$\endgroup$
1
$\begingroup$

(Wikipedia has a very extensively detailed section on vinyl cation rearrangement, so be sure to give it a read as well for a more in-depth view. I'll base my answer on that section)

1,2-hydride shifts are very uncommon in vinyl cations. "The interacting orbitals during the conversion of a linear vinyl cation to a non-linear allyl cation are orthogonal and passes through a non-planar transition state". This leads to a very high activation energy for such a rearrangement. 1,2-methyl shifts too have a very high activation energy.

Hence, even though such a rearrangement would lead to a thermodynamically favorable product, it is uncommon.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.