Karplus-type equations are derived for the variation of one-bond X-Y coupling constants (1)J(X-Y) as a function of dihedral angle for molecules HmX-YHn, for X, Y, =N-15, O-17, P-31, and S-33. Coupling constants were obtained from ab initio EOM-CCSD calculations, with all terms evaluated. The relative orientation of lone pairs appears to be a primary factor determining the dependence of (1)J(X-Y) on the dihedral angle.