STUDY ON THE EFFECT OF THE STRUCTURE OF THE LEAVING GROUP IN THE E1CBMECHANISM OF BASE-PROMOTED BETA-ELIMINATION REACTIONS FROM N-[2-(P-NITROPHENYL)ETHYL]ALKYLAMMONIUM IONS

Studies of acid-base catalysis, H/D exchange, and solvent isotope effe ct on the P-elimination reactions with formation of p-nitrostyrene in acetohydroxamate/acetohydroxamic acid buffers at pH 9.05, H2O, mu = 1 M KCl, 25 degrees C, from N-[2-(p-nitrophenyl)ethyl]alkylammonium ions with different leaving groups, such as N-methylpyrrolidine 1,N-ethylp yrrolidine 2,N-isopropylpyrrolidine 3, N-methylpiperidine 4,N-isopropy lpiperidine 5, and N-methylazepane 6, show a change from a partially r eversible E1cb mechanism with 1, 2, and 4 to an irreversible E1cb mech anism with 3, 5, and 6. The change in the rate-determining step is rel ated to the increased steric requirement of the leaving group. A steri c acceleration from the carbanion intermediate to product step is prop osed.