Monomolecular decay of anion-radicals of isomeric chlorobenzonitriles. Quantum chemical analysis

Abstract

Regularities for the reaction courses of the monomolecular decay of anion-radicals (AR) of isomeric chlorobenzonitriles have been considered basing on the ab initio investigation by ROHF/6-31+G*, MP2/6-31+G*//ROHF/6-31+G*, and B3LYP/6-31+G* methods. Stable structures corresponding to initial AR, final products of the decay, and combining them transition states (TS) of the reaction were localized. The TS found have a substantially non-planar structure. The main factor determining a relative ability of isomeric AR to remove chloride anion is the difference in the density of the unpaired electron on the breaking bond in the initial AR. In the case of para-isomer, whose SOMO is maximally localized on the C atom bonded to Cl, it is likely to expect “ early” TS and low barriers of the reaction both in the gas phase and polar solvents. The fragmentation of ortho-and meta-isomers is forestalled by remarkable structural modifications resulting in the redistribution of electron density with its localization on the breaking bond C—Cl.