Proton magnetic resonance coupling constants and π-bond orders in the active regions of carcinogenic and non-carcinogenic polycyclic hydrocarbons

Abstract

Proton magnetic resonance (PMR) spin-spin coupling constants ( J) depend on the geometry and electronic configuration of the molecule and on its interactions with other molecules. Empirically, ortho coupling constants, J NN′ ortho , in polycyclic hydrocarbons of varying carcinogenicity appear to be related linearly to Hückel molecular-orbital (HMO) π-bond orders, P NN′ , as are the corresponding bond lengths, R NN′ . We find a lack of correlation between J NN′ ortho and carcinogenicity indices; thus there is a relatively large difference in J NN′ ortho for the K region of benz[ a]pyrene and 7,12-dimethylbenz[ a]anthracene, which are both highly active.