Solvation of nitroaromatic radical anions : a molecular orbital investigation of hydrogen bonding models

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Abstract
SCF calculations employing the INDO approximation have been applied to a study of the interaction of water and the nitrobenzene radical anion in order to examine possible mechanisms by which electron spin resonance hyperfine coupling constants are altered when the solvent medium containing the radicals is changed from aprotic to hydroxylic. Calculations have been carried out for hydrogen-bonded radical-water complexes of nine different geometries. None of these calculations agree adequately with the available experimental data. Much better agreement with experiment is obtained if the hydrogen-bond formation is accompanied by a distortion of the nitro group toward a pyramidal conformation. The calculations indicate that this pyramidal distortion, rather than a rotation of the nitro group with respect to the aromatic plane, accompanies hydrogen-bond formation and suggests an experimental method of testing the prediction.