Electronic Current Densities Induced by Magnetic Fields and Nuclear Magnetic Dipoles

The Ramsey theory of nuclear magnetic resonance spectral parameters has been reformulated in terms of current densities induced in the electron cloud of a molecule by an external magnetic field and intramolecular magnetic dipoles at the nuclei. Conditions for invariance of nuclear magnetic shielding and nuclear spin–spin coupling tensors, in gauge transformations of the vector potentials associated to the magnetic perturbations, have been expressed via quantum mechanical sum rules, also providing constraints for charge conservation. It is shown that the combined use of current density and property density maps provides valuable tools for the rationalization of magnetic response.