Knowledge Bank

Expressions for nuclear spin-spin coupling constants (J) in $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Sigma$ molecules are obtained with a generalized valence bond (v.b.) function and second-order perturbation theory. Both electron-spin and electron-orbital contributions are included in the formulation. For evaluating the contact and dipolar spin terms, a modification of the usual Rumer-Pauling rules is developed. “Long-range” approximations for J in the v.b. scheme are introduced and the required integrals are calculated with suitable atomic orbitals. It is found that earlier $estimates1,2$ of some of these integrals are considerably in error. Applications to coupling constants involving $C13$ and $F19$ nuclei are given for typical systems. The v.b. expressions for J derived here are more general in that all terms besides the “contact” term are considered. Further, the present theory is applicable to directly bonded as well as non-bonded nuclei.