Ab initio Evaluation of Intramolecular Electron Transfer Reactions in Halobenzene Radical Anions and Derivatives

ADRIANA B. PIERINI, DOMINGO M. VERA

JOURNAL OF ORGANIC CHEMISTRY

The American Chemical Society

Lugar: New York; Año: 2003 vol. 68 p. 9191 - 9199

0022-3263

<!-- @page { size: 21.59cm 27.94cm; margin: 2cm } P { margin-bottom: 0.21cm } --> The potential energy surfaces for the fragmentation of the radical anions of p-nitrochlorobenzene and p- and m-chloroacetophenones were explored using first principle methods. The behavior of these compounds, stabilized by π acceptors, is compared to that shown by the unsubstituted halobenzenes (PhX, X ) F, Cl, Br, I). The presence of π and σ radical anions was inspected as well as the intramolecular electron transfer (intra-ET) from the π to the σ surface, responsible for the dissociation of these intermediates. The profiles obtained with the B3LYP functional in the gas phase and in the presence of a polar solvent are in agreement with the spectroscopic evidence and with the experimentally observed reactivity of the compounds under study. The stability of the radical anion of p-nitrochlorobenzene and the adiabatic and endothermic nature of its dissociation are explained. The order of the rate constants for dissociation m-chloroacetophenone < p- chloroacetophenone is interpreted on the basis of the differences in the adiabatic character of the intra-ET of both isomers which is ascribed to the nodal properties of their SOMOs. In the halobenzene family, the electronic factors responsible for the intra-ET are analyzed. The stabilization of the σ surface exerted by the different halogens and its effect on the rate constants for dissociation are explained.