Past exam of the chemistry B course of the University of Cambridge / 2024 / Paper 1 / B1 / a / i / Solution

An enolate is an ambident nucleophile: the negative charge is concentrated toward oxygen, while its occupied conjugated orbital also has substantial reactive amplitude at the alpha carbon. An alkyl iodide presents an accessible, polarizable carbon electrophile. carbon attack through an SN2 reaction is generally kinetically favorable, while the more strongly charged oxygen is often coordinated to the counterion or solvated. The carbonyl reforms as the new C–C bond is made.carbon alkylation restores the carbonyl and makes the new C–C bond. oxygen alkylation instead gives an enol ether. The two outcomes are not resonance contributors of one product, and their ratio is not determined just by where the largest formal negative charge is drawn. electrophile, counterion, solvent and aggregation can change selectivity; hard silicon electrophiles and suitable acylating reagents often favor oxygen trapping. Product stability alone would not explain an irreversible kinetic choice.