title: Stereochemical dependence of NMR geminal spin-spin coupling constants.
abstract: In this work it was sought to explore the versatility of geminal 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 (2)K(XY) reduced spin-spin coupling constants (RSSCC), and Rule II(M)-hyperconjugative interactions transferring charge from the coupling pathway yield a negative increase to the FC contribution to (2)K(XY) RSSCC.
authors.affiliation: Department of Physics, FCEyN, University of Buenos Aires and CONICET, Buenos Aires, Argentina.
authors.forename: Rubén H
authors.initials: RH
authors.lastname: Contreras
authors.forename: Patricio F
authors.initials: PF
authors.lastname: Provasi
authors.forename: Francisco P
authors.initials: FP
authors.lastname: dos Santos
authors.forename: Cláudio F
authors.initials: CF
authors.lastname: Tormena