Theoretical Karplus relationships for vicinal coupling constants around χ1 in Valine

Abstract

Karplus coefficients for χ1-related vicinal coupling constants in Valine dipeptide model, obtained from DFT calculations are reported. The computed coefficients agree with available experimental data, excepting C1 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 σ(C–C) and σ(C–H) of the coupling pathway with the vicinal coupling constants is obtained.