A natural bond orbital analysis of hydrocarbon radicals

The methodology of natural bond orbital (NBO) analysis has been applied to the study of alkyl and cyclo-alkyl radicals with the objective of finding relationships between donor/acceptor computed stabilization energies and isotropic Fermi contact couplings (HFCs). A linear correlation was found between computed beta-C-H hyperfine coupling constants and 2nd order perturbation energies, i.e. hyperconjugation. A linear correlation was established between HFCs and the complete range of cos(2) theta of dihedral angles defined by the orbital axes of 2pC-radicals with vicinal beta-C-H* bonds. The dominant spin transmission mechanism is attributed to hyperconjugation with smaller contributions from spin polarization. (C) 2011 Elsevier B.V. All rights reserved.