Abstract
Within the framework of the one-electron MO perturbation method, a simple qualitative model has been developed for positional selectivity of free-radical substitution in the aromatic ring, with which the basic regiochemical trends can be predicted. The dominant trends in regioselectivity of homolytic aromatic substitution are determined by the polar (“philic”) character of the attacking radical and the symmetry of the regiocontrolling MOs are the frontier orbitals and the next (second) HOMOs and LUMOs. In situations in which the attacking radical is distinctly polar relative to the aromatic substrate (where the radical has a nucleophilic or electrophilic character) and the regiocontrolling MO is an orbital of the b1 type (C2v symmetry), ipso attack is possible, with subsequent ipso-ortho rearrangement. In the case of an ambiphilic attacking radical, this probability is very low. The effectiveness of the approach is illustrated in examples of the interaction of various free radicals with monosubstituted benzenes. In addition, other applications of the model are discussed.
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Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 4, pp. 407–414, July–August, 1987.
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Volovik, S.V., Dyadyusha, G.G. & Staninets, V.I. Molecular orbital model of regioselective free-radical aromatic substitution. Theor Exp Chem 23, 380–386 (1988). https://doi.org/10.1007/BF00536354
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DOI: https://doi.org/10.1007/BF00536354