A molecular orbital interpretation of the structure of some halogenoalkyl radicals

Abstract

The conformational preferences and structural trends for a series of fluorine- and chlorine-substituted methyl and ethyl radicals are rationalized. The methodology used to analyse the pyramidality of substituted methyl radicals is based upon a quantitative decomposition of the molecular orbitals for the pyramidal structure in terms of the molecular orbitals for the planar form. A second-order perturbation treatment is also applied in order to have a simple approximation to the aforementioned decomposition. Using these methods it is possible to evaluate quantitatively the relative contributions of electronegativity and conjugation effects in determining the extent of pyramidality of the radicals. It is shown that the electronegativity of the substituents plays the major role. The conformational preferences for β-halogenoethyl radicals are also discussed. The calculations are of the MNDO type with UHF and half-electron formalisms