Kinetics and mechanisms of nucleophilic displacements with heterocycles as leaving groups. Part 22. Reactions with various nucleophiles and a study of the effects of substrate concentration, traces of water, and nature of the gegenion on the rates

Abstract

First- and second-order rate components for the nucleophilic displacements of a variety of N-(primary alkyl), N-(secondary alkyl), and N-benzyl substituents from mono-, bi-, and tri-cyclic pyridine leaving groups by various nucleophiles are indepnedent of substrate concentration, of the nature of the gegenion, and of traces of water in the solvent. Thus assumptions implicit in the reasoning of earlier papers of this series are confirmed, and the conclusion that these nucleophilic displacements can, proceed by five independent mechanistic pathways is strengthened.

First-order rate components are invariant with the nature of the nucleophile. Second-order rate components vary with nucleophile nucleophilicity in a way that parallels Menschutkin reactions. Activation enthalpies for first-order components are less negative than those for second-order components, in agreement with previous data.