Stereochemical dependence of NMR geminal spin-spin coupling constants

In this work it was sought to explore the versatility of germinal spin-spin coupling constants, (2)J(XY) SSCCs, as probes for stereochemical studies. A set of compounds, where their experimental (2)J(XY) SSCCs through the X-C-Y molecular fragment are predicted to be sensitive to hyperconjugative interactions involving either bonding or antibonding orbitals containing the C carbon atom ('coupling pathway'), were analyzed. SSCC calculations were performed for some selected examples using the second order polarization propagator approximation (SOPPA) method or within the DFT-B3LYP framework. Hyperconjugative interactions were calculated within the Natural Bond Orbital (NBO) approach. Results are condensed in two qualitative rules: Rule I-M - hyperconjugative interactions transferring charge into the coupling pathway yield a positive increase to the Fermi contact (FC), contribution to K-2(XY) reduced spin-spin coupling constants (RSSCC), and Rule IIM - hyperconjugative interactions transferring charge from the coupling pathway yield a negative increase to the FC contribution to K-2(XY) RSSCC. Copyright (C) 2008 John Wiley & Sons, Ltd.