Density functional theory studies on radical ions of selected polychlorinated biphenyls

Density functional theory studies provided the adiabatic ionization potentials and electron affinities of six polychlorinated biphenyls (PCBs): 3,3',4,4'- and 2,2',5,5'-tetrachlorobiphenyl; 3,3',4,4,5-, 2,2',4,5,5'-, and 2,3',4,4',5-pentachlorobiphenyl; and 3,3',4,4',5,5'-hexachlorobiphenyl. A popular three-parameter hybrid functional (B3LYP) with the 6-311G(d,p) and 6-311+G(2d,2p) basis sets was used for this study. We present the optimized structures of the cations and anions of the selected PCBs at the B3LYP/6-311+G(2d,2p) level. In almost all of the studied PCBs,the structure of the ions tended to be more nearly planar than the structure of the corresponding neutrals. The radical ions of 2,2',5,5'-tetrachlorobiphenyl and 2,2',4,5,5'-pentachlorobiphenyl have energetically close syn- and antilike structures. The anions of non-ortho-chlorinated PCBs have coplanar structures. Ionization potentials obtained at the B3LYP/6-311+G(2d,2p) level were 8.07, 8.34, 8.16, 8.36, 8.20, and 8.26 eV for 3,3',4,4'- and 2,2',5,5'-tetrachlorobiphenyl, 3,3',4,4',5-, 2,2',4,5,5'-, and 2,3',4,4',5-pentachlorobiphenyl, and 3,3',4,4',5,5'-hexachlorobiphenyl, respectively. Adiabatic electron affinities obtained for all of the selected PCBs were positive and larger than the electron affinity of biphenyl. Furthermore, the electron affinities of the non-ortho-chlorinated PCBs were higher than those of their ortho-substituted counterparts.