Acid-catalyzed hydration (H₃O⁺) of 1-vinylcyclobutane leads to a rearranged alcohol as the major product. What is the structure of this product?
- 1-ethylcyclobutanol
- 1-vinylcyclobutanol
- 1-methylcyclopentanol (correct answer)
- 2-methylcyclopentanol
Explanation: The mechanism begins with protonation of the vinyl group's terminal carbon, following Markovnikov's rule, to form a secondary carbocation on the carbon attached to the cyclobutane ring. This carbocation is adjacent to a strained four-membered ring. A ring expansion occurs where a C-C bond in the ring breaks and reforms with the cationic carbon, expanding the four-membered ring to a less-strained five-membered ring. This rearrangement produces a tertiary carbocation on the cyclopentane ring (at the carbon that was originally part of the vinyl group). Water then attacks this stable tertiary carbocation, and after deprotonation, the final product is 1-methylcyclopentanol. The stereocenter is not formed as the carbon attacked is prochiral and the intermediate is planar, leading to a racemic mixture if applicable, but the question asks for the structure.