JEE Main · 2023 · 29 Jan 2023 · Shift 2 · Alcohols Phenols and Ethers

Acid protonates the hydroxyl group and water leaves, generating a secondary carbocation on the carbon just outside the five-membered ring. This cation is relieved when a ring carbon$-$carbon bond migrates to it, expanding the cyclopentane ring to a cyclohexane ring and shifting the positive charge onto the more stable tertiary centre, which now carries a methyl group next to a second methyl-bearing carbon. Loss of a proton in accordance with Zaitsev's rule then forms the most highly substituted alkene, with the double bond lying between the two methyl-bearing ring carbons. The major product is 1,2-dimethylcyclohex-1-ene.