The anisotropy of the g -factor for polycyclic hydrocarbons

Abstract

An external magnetic field acting on a polycyclic hydrocarbon induces ring currents of mobile electrons in its various rings. This effect can be observed in a diamagnetic molecule by means of the large anisotropies of diamagnetic susceptibility and chemical shift which are produced. For paramagnetic species these observations are no longer available and it is suggested that the anisotropy of the electronic g-factor should be used instead. This arises because the secondary magnetic field of the ring currents helps to orient the electron spins. In the Hamiltonian it is the spin-other-orbit term which produces this interaction. The magnitude of this term is calculated for various species using the unrestricted molecular orbital theory in its self-consistent form and $\Delta$g$_{zz}$ is of the order 3 x 10$^{-5}$.