Computed Spin-Spin Coupling Constants (1JX-Y) in Molecules HmX-YHn for X and Y = 13C, 15N, and 31P: Comparisons with Experiment and Insights into the Signs of 1JX-Y
One-bond X−Y spin−spin coupling constants (1JX-Y) for 18 HmX−YHn molecules, with X and Y =13C, 15N, and 31P, have been computed using the equation-of-motion coupled-cluster singles and doubles method. The molecules investigated include all possible combinations of these three elements bonded with single, double, and triple bonds. The computed coupling constants are in good agreement with experiment over a range that extends from −250 to +200 Hz. With only two exceptions, the sign of the Fermi-contact (FC) term is the same as the sign of 1JX-Y, but the FC term may or may not be a good quantitative estimate of 1JX-Y. When reduced spin−spin coupling constants (1KX-Y) are used for comparing coupling constants involving different atoms, a linear relationship is observed between 1KX-N and 1KX-P. The signs of 1JX-Y for approximately half of the molecules included in this study are exceptions to the Dirac vector model. The recently proposed NMR triplet wave function model has been used to provide insight into the variation of the signs of these one-bond spin−spin coupling constants.