Molecular complexes. Part 18.—A nuclear magnetic resonance adaptation of the continuous variation (job) method of stoicheiometry determination

Abstract

An n.m.r. counterpart of the classical Job method for determining the stoicheiometry of molecular complexes by spectrophotometry is derived. It is applied to the fluoranil–hexamethylbenzene and acetonitrile–benzene systems, for which stoicheiometries consistent with those deduced classically are obtained, although for the latter system an additional complex is identified. The method is used to reveal the dependence of the measured stoicheiometry on the solution concentration of the interacting species. It is demonstrated that 1:1 and 1:2 complexes can be identified separately when they coexist, and that the equilibrium constant for the formation of the former can be measured readily.