Pyridine nitrogen reactivity

Abstract

Pyridinium pK_a values and rates of quaternization with ethyl iodide in various solvents are used to evaluate the effect of substituents on the pyridine nitrogen reactivity. Substituent effects on nitrogen reactivity are found to be intrinsic properties of the pyridine system independent of specific reaction type or solvent. The relevance of hydrogen-bonding in methanol and its influence on pyridine quaternization is discussed. The influence of potential resonance acceptors is shown to be due to their inductive effect alone, and the general question of the applicability of the dual substituent parameter equation to substituent effects on nitrogen reactivity in pyridine is considered.