Interpretation of vicinal spin–spin coupling constants in ethane via the current-density induced by nuclear magnetic dipoles

The indirect nuclear spin–spin coupling is rationalized via electronic current densities induced by nuclear magnetic dipoles. The coupling-density tensor, a function in real space obtained from the current density, visualizes fundamental aspects of the coupling mechanism. Magnetic group theory and current-density plots are used for discussing the Dirac–van Vleck vector model in the contact interaction. The Biot–Savart law is useful for understanding the sign of the contributions to the magnetic field at a nucleus from a given point of the current field. These tools are used to analyze the vicinal spin–spin coupling in ethane.