Relativistic Force Field: Parametrization of 13C-1H Nuclear Spin-Spin Coupling Constants

Previously, we reported a reliable DU8 method for natural bond orbital (NBO)-aided parametric scaling of Fermi contacts to achieve fast and accurate prediction of proton-proton spin-spin coupling constants (SSCC) in H-1 NMR. As sophisticated NMR experiments for precise measurements of carbon proton SSCCs are becoming more user-friendly and broadly utilized by the organic chemistry community to guide and inform the process of structure determination of complex organic compounds, we have now developed a fast and accurate method for computing C-13-H-1 SSCCs. Fermi contacts computed with the DU8 basis set are scaled using selected NBO parameters in conjunction with empirical scaling coefficients. The method is optimized for inexpensive B3LYP/6-31G(d) geometries. The parametric scaling is based on a carefully selected training set of 274 ((3)J), 193 ((2)J), and 143 ((1)J) experimental C-13-H-1 spin spin coupling constants reported in the literature. The DU8 basis set, optimized for computing Fermi contacts, which by design had evolved from optimization of a collection of inexpensive 3-21G*, 4-21G, and 6-31G(d) bases, offers very short computational (wall) times even for relatively large organic molecules containing 15-20 carbon atoms. The most informative SSCCs for structure determination, i.e., (3)J, were computed with an accuracy of 0.41 Hz (rmsd). The new unified approach for computing H-1-H-1 and C-13-H-1 SSCCs is termed DU8c.