Sum-over-states calculation of the nuclear spin–spin coupling constants

Nuclear spin–spin coupling constants calculated using the sum-over-states (SOS) expansions were compared to experimental values and usual coupled-perturbed (CP) calculations. Rigid Kohn–Sham orbitals obtained from a hybrid density functional were used in the SOS model. Its accuracy for small molecules is comparable with the CP results, nevertheless calculated constants were uniformly underestimated. However, the SOS scheme is less limited by molecular size and can be applied for bigger systems than the CP method, as documented on the proton–proton coupling constants in α-pinene, β-pinene, and camphor molecules.