The theory of chemical shifts in nuclear magnetic resonance I. Induced current densities

The chemical shifts of nuclear magnetic resonance frequencies are determined by the secondary magnetic field due to the electronic current induced by the applied field. This paper is concerned with the general problem of finding the current density vector field. An approximate orbital theory is developed which enables this to be divided up, under certain conditions, into local diamagnetic and paramagnetic circulations about individual atoms. The method is applied to the acetylene molecule as an example.