THEORETICAL-STUDY ON HALOAROMATIC RADICAL-ANIONS AND THEIR INTRAMOLECULAR ELECTRON-TRANSFER REACTIONS

An AM1 theoretical study was made on the electronic nature of radical anions of halobenzenes, 2-halopyridines, halobenzonitriles, ortho-, pa ra-, meta-haloacetophenones and related compounds (X = Cl, Br and I). The experimentally determined fragmentation rate of these intermediate s is discussed in terms of the possibility of the existence of pi and sigma orbital isomeric radical anions, their energy difference and t he probability of an intramolecular electron-transfer reaction from th e pi to the sigma* system. Good correlation was obtained between the properties determined theoretically and the experimental fragmentation rates for the family of halobenzonitrile and haloacetophenone compoun ds. Inspection of the potential surface for the intramolecular electro n-transfer reaction between both isomers indicates that the carbon-hal ogen bond elongation and bending angle are the main reaction coordinat es for the electron-transfer step which results from an avoided crossi ng of potential energy surfaces (non-vanishing H-sigma pi integral).