See image — Haloalkanes and Haloarenes Chemistry Question

💡 Solution & Explanation

Concept: Moist Ag2O acts as a mild base/nucleophile source and promotes intramolecular rearrangement (ring expansion) via a carbocation or neighboring-group-participation mechanism when a suitable substrate is present. Step 1 – Identify the substrate: The starting material is 1-(bromomethyl)-1-methylcyclopentane, i.e., a cyclopentane ring bearing both a –CH2Br (primary alkyl bromide) and a –CH3 group on the same ring carbon (C1). This is a neopentyl-type (primary) bromide that cannot easily undergo simple SN2 due to steric crowding at the adjacent quaternary carbon. Step 2 – Reaction with Ag2O (moist): Silver oxide (Ag2O) with moisture acts as AgOH in situ. Ag+ abstracts Br– to ionize the C–Br bond, generating a primary carbocation at the exocyclic –CH2+ position adjacent to the quaternary ring carbon. Step 3 – 1,2-Ring expansion (Wagner–Meerwein shift): The primary carbocation at –CH2+ is very unstable. A 1,2-alkyl shift occurs: one of the C–C bonds of the cyclopentane ring migrates to the exocyclic carbocation center. This converts the 5-membered ring into a 6-membered ring, simultaneously moving the positive charge onto a tertiary carbon (the former ring carbon that bore the methyl group). This gives a tertiary carbocation on a cyclohexane ring with a methyl group at that carbon (C1 of the new cyclohexane). Step 4 – Trapping by OH–: The tertiary carbocation (1-methylcyclohexyl cation) is trapped by the hydroxide (from moist Ag2O/AgOH) to give 1-methylcyclohexan-1-ol, a tertiary alcohol. Step 5 – Why the other options fail: - Option (a): Simple SN2 substitution at the primary carbon without rearrangement. This is disfavored because the adjacent quaternary carbon blocks backside attack; moreover, the ring expansion to a more stable tertiary carbocation is strongly preferred. - Option (b): Would require a different kind of rearrangement product inconsistent with the ring expansion pathway. - Option (d): 2-methylcyclohexan-1-ol would arise from a secondary carbocation intermediate, which is less stable than the tertiary carbocation formed in the ring expansion; thus it is not the major product. The ring expansion from cyclopentylmethyl to cyclohexyl system (Wagner–Meerwein) giving the tertiary alcohol is the major pathway. Therefore, the correct answer is C.