Electron-coupled “through-space” nuclear spin–spin interaction

Abstract

The evidence for a “through-space” contribution to the nuclear spin-coupling constant J_AB is reviewed. There is a large contribution to the coupling of fluorine nuclei. Through-space coupling is attributed to the Fermi contact interaction of nuclear and electron spins and to the transfer of electron spin between atoms A and B by the overlap of localised molecular orbitals. A semi-empirical theory is proposed in which through-space coupling is assumed to be proportional to the atomic valence s electron density at the A and B nuclei and to the square of the overlap integral of these atomic s orbitals. The theory is capable of rationalising the observed spin-coupling constants of the alkali-metal halide molecules and provides a reasonable description of fluorine–fluorine coupling.