The carbonyl-carbon kinetic isotope effect (KIE) and the substituent effect were measured for the reaction of lithium pinacolone enolate (CH2 C (OLi) C (CH3) 3) with benzaldehyde, and the results were compared with those for other lithium reagents such as MeLi, PhLi, and CH2 CHCH2Li. Ab initio MO calculations (HF/6-31+ G*) were carried out to estimate the equilibrium IE on the addition to benzaldehyde. A carbonyl addition reaction, in general, ...