Critique of the multipath model for 1J(C,C) nuclear spin-spin coupling via electron current induced by 13C nuclear magnetic dipoles

Maps of ab initio electronic current density induced by the permanent magnetic dipole moment of 13C are reported for three saturated hydrocarbons: ethane, cyclopropane, and bicyclobutane. The plots are interpreted via the Biot-Savart law of classical electromagnetic theory by analysing the effects of the magnetic field induced by the current distribution at the site of spin-coupled carbon nuclei. It is shown that, within the proposed model, the significant variation in magnitude and sign of 1J(C,C) characterising these three molecules can be related to different topologleal features of the current density vector field. The general pattern can be rationalised in terms of orbital hybridisation of the coupled carbon atoms: 1J(C,C) does not appear to be significantly affected by the multipath coupling processes usually suggested in the literature. © 2006 Wiley-VCH Verlag GmbH & Co. KGaA.