Predicted signs of reduced two-bond spin-spin coupling constants (2hKX-Y) across X-H-Y hydrogen bonds

The reduced two-bond Fermi-contact terms and the reduced spin-spin coupling constants (2h)K(X-Y) across X-H-Y hydrogen bonds for complexes stabilized by C-H-N, N-H-N, O-H-N, F-H-N, C-H-O, O-H-O, F-H-O and C-H-F hydrogen bonds are positive. The NMR Triplet Wavefunction Model (NMRTWM) indicates that the signs of the reduced FC terms and (2h)K(X-Y) are determined by excited triplet states that have an odd number of nodes intersecting the X-Y axis between X and Y, thereby leading to an antiparallel alignment of the nuclear magnetic moments of atoms X and Y.