Anisotropy of the indirect nuclear spin-spin coupling constant

Anisotropies in the indirect nuclear spin-spin coupling constants arise from cross-terms between the contact and dipolar terms in the electron-nuclear Hamiltonian. Calculated anisotropic H-H and 13C-H coupling constants. which are based on valence-bond wavefunctions. are non-negligible in comparison with the isotropic coupling constants, but are much smaller than the direct dipole-dipole coupling constants.