Propose a mechanism for the following reaction:
Step 1 of 4</p>
The mechanism is shown as follows:
Heterolytic cleavage of carbon and halogen gives a stable carbocation.
Step 2 of 4</p>
Even though the rearrangement step transforms a stable tertiary carbocation into a less stable secondary cation, relief of strain in expansion forms a four five membered ring makes the alkyl migration favorable. Five membered rings are more stable than four membered rings due to less strain.