The aldol addition of acetone to aldehydes 1-5 is catalyzed by primary amine 14. The pH profile is consistent with catalysis by the free amine, with PKa= 8.55 for its conjugate acid. The catalytic cycle involves rate-determining coupling of the aldehyde with enamine I11 formed by condensation of the amine and acetone. Condensation with the aldehyde to form imine 16 inhibits catalysis (Kl6= 7.8 mM). Assembly of amine 14 with an antibody against ...