Mechanism and proton activating factors in base-induced beta-elimination reactions of N[2-(4-pyridyl)ethyl]quinuclidinium and N-[2-(2-pyridyl)ethyl]quinuclidinium salts

beta-Elimination reactions of N-[2-(4-pyridyl)ethyl]quinuclidinium and N-[2 -(2-pyridyl)ethyl]quinuclidinium salts (N) in acetohydroxamate-acetohydroxa mic acid buffer, H2O, mu = 1 M KCl, 50 degrees C, with the formation of 4- or 2-vinylpyridine, respectively, proceed by an E1cb mechanism with carbon deprotonation occurring in the substrates protonated at the pyridine ring ( NH+). The formation of the intermediate carbanion has a high degree of reve rsibility. The systems consistently present H/D exchange. NH+ is much more reactive than N; this can be attributed to the strong stabilization of the intermediate carbanion formed from NH+ due to resonance.