Question

Question: Sometimes carbocation rearrangements can change the size of a ring. Draw a stepwise, detailed mechanism for the following reaction.

Short answer

Answer

Step-by-step solution

Step-by-Step SolutionStep 1: Dehydration of alcohols

The incorporation of acid like ${\mathbf{H}}_{\mathbf{2}}{\mathbf{SO}}_{\mathbf{4}}$to alcohol leads to the formation of alkene. These reactions belong to the category of elimination reactions.

Carbocation rearrangement

The transformation of the carbocation from its unstable state to a stable state can be referred to as carbocation rearrangement. Alcohols can be turned into carbocations with the help of carbocation rearrangement.

Stepwise mechanism for the reaction

The first step is the protonation of the oxygen atom that converts a poor leaving group to an excellent leaving group.

The first step of the reaction mechanism

The second step involves the cleavage of the C-O bond leading to the formation of a carbocation intermediate. This step is slow and is the rate-determining step

The second step of the reaction mechanism

A secondary carbocation is not stable and gets stabilized by 1,2-shift leading to the formation of a tertiary carbocation.

The third step of the reaction mechanism

The third step is the abstraction of a proton from a carbon adjacent to the carbocation to form the desired alkene.

The fourth step of the reaction mechanism