The o-, m-, p-halobenzyl radicals and their anions: Structures and electron affinities

Abstract

The molecular structures, and electron affinities of the ortho, meta, and para isomers of the fluorobenzyl, chlorobenzyl, and bromobenzyl species have been determined using five hybrid Hartree–Fock/density functional methods.The basis set used in this work is of double-ζ plus polarization quality with additional diffuse s- and p-type functions, denoted DZP++.These methods have been carefully calibrated [Rienstra-Kiracofe, Tschumper, Schaefer, Nandi, Ellison, Chem.Rev.102 (2002) 231].The geometries are fully optimized with each DFT method and discussed, respectively.Three different types of the neutral–anion energy separations reported in this work are the adiabatic electron affinity (EA ad), the vertical electron affinity (EA vert), and the vertical detachment energy (VDE). The most reliable adiabatic electron affinities (with ZPVE correction), obtained at the DZP++ BPW91 level of theory, are 1.093 ( o-FC 6H 4CH 2 ), 1.240 ( o-ClC 6H 4CH 2 ), 1.292 ( o-BrC 6H 4CH 2 ), 1.165 ( m-FC 6H 4CH 2 ), 1.270 ( m-ClC 6H 4CH 2 ), 1.314 ( m-BrC 6H 4CH 2 ), 0.957 ( p-FC 6H 4CH 2 ), 1.172 ( p-ClC 6H 4CH 2 ), and 1.237 eV ( p-BrC 6H 4CH 2 ), respectively.Compared with the experimental values, the average absolute error of the BPW91 method is 0.009 eV. The B3LYP and BLYP functionals also gave excellent predictions, with average absolute errors of 0.026 and 0.061 eV, respectively.In addition, for a given halogen substituent, the para isomer has the smallest electron affinity and the meta isomer has the largest.Lastly, the BPW91 method also predicted the adiabatic electron affinities of other halogen substituted benzyl radicals to be 1.512 (FClC 6H 3CH 2 ), 1.550 (FBrC 6H 3CH 2 ), 1.638 (ClBrC 6H 3CH 2 ), 1.418 (F 2C 6H 3CH 2 ), 1.602 (Cl 2C 6H 3CH 2 ), 1.673 (Br 2C 6H 3CH 2 ), 1.439(F 3C 6H 2CH 2 ), 1.709 (Cl 3C 6H 2CH 2 ), 1.793 (Br 3C 6H 2CH 2 ), 1.733 (F 4C 6HCH 2 ), 2.031 (Cl 4C 6HCH 2 ), 2.114 (Br 4C 6HCH 2 ), 1.785 (F 5C 6CH 2 ), and 2.120 eV (Cl 5C 6CH 2 ), respectively.