Calculation of nuclear spin-spin couplings IX. Vicinal proton-proton coupling constants in methanol and methylamine

Abstract

Ab initio self-consistent field and Møller–Plesset perturbation calculations have been carried out for the dihedral angle (φ) dependence of the vicinal proton–proton coupling constants (³ J _HH) in methanol and methylamine. The four contributions to the ³ J _HH have been computed. The Fermi-contact (FC) contribution was largest and the spin–dipolar contribution was smallest. The orbital paramagnetic and diamagnetic contributions provided comparable magnitudes of opposite signs. The second-order correlation was large but the third-order one was very small. The addition of the tight s-type functions increased the FC contribution. The calculated curves for ³ J _HH versus φ reproduced the experimental ones well.

Notes

The s- and p-type contracted Gaussian orbitals are taken from Dunning Jr, T. H., 1971, J. chem. Phys., 55, 716; and the polarization functions are taken from 6-311G** basis sets by Krishnan, R., Binkley, J. S., Seeger, R., and Pople, J. A., 1980, J. chem. Phys., 72, 650.