Theoretical study on haloaromatic radical anions and their intramolecular electron transfer reactions

Abstract

An AM1 theoretical study was made on the electronic nature of radical anions of halobenzenes, 2-halopyridines, halobenzonitriles, ortho-, para-, meta-haloacetophenones and related compounds (X = Cl, Br and I). The experimentally determined fragmentation rate of these intermediates is discussed in terms of the possibility of the existence of π* and σ* orbital isomeric radical anions, their energy difference and the probability of an intramolecular electron-transfer reaction from the π* to the σ* system. Good correlation was obtained between the properties determined theoretically and the experimental fragmentation rates for the family of halobenzonitrile and haloacetophenone compounds.

Inspection of the potential surface for the intramolecular electron-transfer reaction between both isomers indicates that the carbon–halogen bond elongation and bending angle are the main reaction coordinates for the electron-transfer step which results from an avoided crossing of potential energy surfaces (non-vanishing H_σπ integral).