Comprehensive ab initio studies of nuclear magnetic resonance shielding and coupling constants in XH center dot center dot center dot O hydrogen-bonded complexes of simple organic molecules

The influence of hydrogen-bond formation on the scalar spin-spin coupling c onstants and NMR shielding constants in CH2O-H2O, C2H2-H2O, CH3OH-H2O, and (HCOOH)(2) complexes has been calculated using correlated MO (MCSCF and MP2 ) methods. The hydrogen-bond transmitted spin-spin coupling constants are a lso reported. The iso- and anisotropic H-1 shielding constants are found to be the most general parameters of the hydrogen bond. The changes in (1)J(X H) coupling in the proton donor also correlate with the XH ... Y hydrogen b ond strength. A similar correlation is found in the intermolecular (1h)J(HY ) and (2h)J(XY) couplings. These couplings are substantial and dominated by the Fermi-contact term in contrast to the longer-range hydrogen-bond trans mitted couplings where the noncontact terms prevail. (C) 2000 American Inst itute of Physics. [S0021-9606(00)30618-3].