Which of the following alkyl halides is most likely to undergo rearrangement in an sn1 reaction?

(a) 1-bromo-4-methylcyclohexane

(b) 2-chloro-3,3-dimethylpentane

(c) 3-bromopentane

(d) bromocyclohexan

(b) 2-chloro-3,3-dimethylpentane

Explanation:

A rearrangement occurs in a SN1 reaction when the carbocation is formed. More substituted carbocations are more stable because of the electron-donating effect of alkyl groups and the hyperconjugation.

An alkyl halide with a carbon more substituted than the carbon where is the C-X bond, is most likely to undergo rearrangement.

(a) 1-bromo-4-methylcyclohexane

In this molecule could occur a rearrangement but the carbocation need to jump three bonds.

(b) 2-chloro-3,3-dimethylpentane

This alkyl halide is most likely to occur a rearrangement because the near carbon is a quaternary carbon.

(c) 3-bromopentane

Can't occur a rearrangement because all carbons are secondary

(d) bromocyclohexane

Also, can't occur a rearrangement because all carbons are secondary.

Thus, the most likely to undergo rearrangement in an SN1 reaction is (b) 2-chloro-3,3-dimethylpentane

I hope it helps!