Theoretical Karplus relationships for vicinal coupling constants around χ1 in Valine

Karplus coefficients for chi 1-related vicinal coupling constants in Valine dipeptide model, obtained from DFT calculations are reported. The computed coefficients agree with available experimental data, excepting C-1 coefficient that is obtained with negative sign. This apparently anomalous coefficient sign is analyzed within NBO methodology. From this analysis a relationship between the hyperconjugation of the bonding orbitals sigma(C-C) and sigma(C-H) of the coupling pathway with the vicinal coupling constants is obtained. (C) 2007 Elsevier B.V. All rights reserved.