184. Stereochemical dependence of NMR geminal spin-spin coupling constan

RUBÉN H. CONTRERAS, PATRICIO F. PROVASI, FRANCISCO P. DOS SANTOS AND CLÁUDIO F. TORMENA,

MAGNETIC RESONANCE IN CHEMISTRY

John Wiley and Sons

Lugar: Chichester, UK; Año: 2009 vol. 47 p. 113 - 120

0749-1581

In this work it was sought to explore the versatility of geminal spin–spin coupling constants, 2JXY SSCCs, as probes for stereochemical studies. A set of compounds, where their experimental 2JXY 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 IM – hyperconjugative interactions transferring charge into the coupling pathway yield a positive increase to the Fermi contact (FC), contribution to 2KXY 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 2KXY RSSCC.geminal spin–spin coupling constants, 2JXY SSCCs, as probes for stereochemical studies. A set of compounds, where their experimental 2JXY 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 IM – hyperconjugative interactions transferring charge into the coupling pathway yield a positive increase to the Fermi contact (FC), contribution to 2KXY 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 2KXY RSSCC.2JXY 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 IM – hyperconjugative interactions transferring charge into the coupling pathway yield a positive increase to the Fermi contact (FC), contribution to 2KXY 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 2KXY RSSCC.M – hyperconjugative interactions transferring charge into the coupling pathway yield a positive increase to the Fermi contact (FC), contribution to 2KXY 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 2KXY RSSCC.2KXY 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 2KXY RSSCC.2KXY RSSCC.