Ab Initio IGLO Studies of the Conformational Dependence of the γ-Effect in the 13C NMR Spectra of Cyclic Hydrocarbons

摘要: Ab initio IGLO (individual gauge for localized molecular orbital) methods of SCF-MO theory are used to study and analyze the mathematical form angular dependence γ-effects which often observed in 13C NMR spectra cyclic hydrocarbons. Isotropic shielding calculations were performed as a function dihedral angle propane, n-butane, i-butane, 2-methylbutane, 2,3-dimethylbutane. Since usually determined chemical shift differences molecule hydrogen is replaced by substituent (e. g., methyl), three models obtained taking these molecules pairs. The dependencies arising from each model compared with experimental data have been reported series rigid bicyclic molecules. Only most general trends followed simplest γ-effect n-butane/propane data. Better correspondence found based on 2-methylbutane 2,3-dimethylbutane asymmetry agreement shows that depends both stereochemistry.