Operationism, mechanism, and high pressure (Modern aspects of physical chemistry at high pressure : the 50th commemorative volume)

Abstract

A critique of the Langford-Gray operational approach to ligand substitution mechanisms is given. Difficulties arising from the manner in which associative and dissociative interchange (I_a I_d) processes are defined are examined. Alternative operational criteria based on pressure effects give a clear categorization of solvent exchange reactions which corresponds to the traditional S_N1/S_N2 dichotomy and which correlates well with other evidence regarding the modes of activation of net substitution reactions at the same centres. Conflicts between mechanistic assignments based on ostensibly equivalent but independent operational criteria illustrate fundamental limitations of operationism.