C.A. Coulson's work on a contour-integral approach to the London theory of magnetic susceptibility of conjugated molecules

Abstract

Mizoguchi has very recently cast London's theory of magnetic susceptibilities of conjugated molecules in terms of the Coulson contour-integral formulation of Hückel molecular-orbital theory. Since interest in this approach has been thus revived, we present here a previously unpublished document, dated May 16th, 1953, by the late Professor C.A. Coulson, FRS, in which he formulates the London theory in terms of his own contour-integral method. Coulson's treatment is based on bond-bond polarisabilities and it therefore provides an interesting parallel to certain aspects of the now-classic McWeeny polarisability method, advanced five years later. The Coulson polarisability formalism does not, however, provide for explicit computation of individual “ring-current” intensities, nor — since it preceded the experimental observations — for the direct calculation of “ring-current” secondary fields (and, hence,¹H-NMR chemical shifts).