Q1(h). Pinacol rearrangement with ring expansion

Answer in brief

Pinacol rearrangement with ring expansion gives spiro[3.4]octan-5-one .

Key points

• H⁺ protonates one OH; loss of H₂O (rate-determining) gives a tertiary carbocation on a cyclobutane carbon.
• A ring C–C bond of the other cyclobutane migrates to C⁺ (1,2-shift). That ring becomes five-membered, and the carbon carrying OH becomes C⁺ stabilised by O.
• Driving forces: relief of cyclobutane strain and formation of the oxocarbenium ion (all atoms with octets), which loses H⁺ to give C=O.
• The cation's own ring is kept, so the product is a spiro ketone with C=O next to the spiro carbon: C₈H₁₄O₂ → C₈H₁₂O + H₂O.