www.mdpi.org/ijms/ The Spin–Spin Coupling Constants in Ethane, Methanol and Methylamine: A Comparison of

Abstract: The spin–spin coupling constants in ethane, methylamine, and methanol have been calculated using density-functional theory (DFT), coupled-cluster singlesand-doubles (CCSD) theory, and multiconfigurational self-consistent field (MCSCF) theory so as to benchmark the performance of DFT against high-level ab initio methods and experimental data. For each molecule, the Karplus curve has been evaluated at the three computational levels. The comparisons with ab initio methods indicate that DFT reproduces the 1 J(CH), 1 J(CC), and 1 J(NH) one-bond couplings well but is less accurate for 1 J(CN), 1 J(OH), and 1 J(CO). While DFT performs well for the geminal couplings 2 J(HH) and 2 J(CH), it tends to overestimate the vicinal 3 J(HH) couplings slightly although it is sufficiently accurate for most purposes