Molecular Orbital Treatment of Nitric Oxide Radicals. II. ESR Spectra of Aliphatic Nitric Oxide Radicals

Quantitative discussions of the ESR spectra of aliphatic nitric oxide radicals have been undertaken on the basis of the molecular orbitals of all-valence-electrons, which were evaluated by the approximate SCF method with the CNDO/2 approximation. The spin density on the methyl proton in the dimethyl nitric oxide radical is proportional to cos2θ, where θ is the angle between the nitrogen 2pz orbital and the plane containing the C–N and the G–H bonds; the small hyperfine splitting constants of β-protons appearing in some substituted nitric oxide radicals are understood as resulting from the sterically-restricted conformations of substituted groups. The deviation of the g factor of aliphatic nitric oxide from the free spin comes from the large spin densities localized on the nitrogen and the oxygen atoms, and the small excitation energy, from the nonbonding orbital of the oxygen to the odd π-orbital. The electronic structures and g factors of some other radicals are compared to those of aliphatic nitric oxide radicals.