Study on the Effect of the Structure of the Leaving Group in the E1cb Mechanism of the Base-Promoted β-Elimination Reactions from N-alkylammonium Ions

Article abstract of DOI:10.1021/jo00131a011

Studies of acid-base catalysis, H/D exchange, and solvent isotope effect on the β-elimination reactions with formation of p-nitrostyrene in acetohydroxamate/acetohydroxamic acid buffers at pH 9.05, H2O, μ = 1 M KCl, from N-<2-(p-nitrophenyl)ethyl>alkylammonium ions with different leaving groups, such as N-methylpyrrolidine 1, N-ethylpyrrolidine 2, N-isopropylpyrrolidine 3, N-methylpiperidine 5, and N-methylazepane 6, show a change a partially reversible E1cb mechanism with 1, 2, and 4 to an irreversible E1cb mechanism with 3, 5, and 6.The change in the rate-determining step is related to the increased steric requirement of the leaving group.A steric acceleration from the carbanion intermediate to product step is proposed.