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.


(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.


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