A semi-empirical approach to the estimation of ESR isotropic hyperfine coupling constants in aromatic radicals

Abstract

Using a generalised product wave function, an expression is given for the isotropic hyperfine coupling constant at a given atom in an aromatic π-radical. By a consistent scheme of approximation the expression is cast in a form in which the coupling constant at a given atom in the radical can be evaluated from the results of a Huckel calculation, provided that certain integrals are known. A scheme for assigning and relating these integrals is given, coupling constants are calculated for 13C, 14N, 17O and 19F atoms, and the calculations compared with experiment.