The coupling between an unpaired electron spin and a proton two bonds away

In certain stable free radicals the unpaired electron, predominantly localized on a carbon atom, interacts magnetically with protons two bonds removed, with consequent hyperfine structure of the electron spin resonance spectrum. The anisotropic component of the coupling tensor which describes the interaction is assumed to have two important contributions : (1) the direct dipole-dipole interaction of the free spin localized on the carbon atom; (2) the effect of free spin on the intervening atom. The magnitude of the latter effect is deduced from the experimental isotropic coupling constant. The calculated anisotropic coupling tensors are compared with experimental values.