Electron affinities (EAs) and free energies for electron attachment (DeltaGo(a,298K)) have been directly calculated for 45 polynuclear aromatic hydrocarbons (PAHs) and related molecules by a variety of theoretical methods, with standard regression errors of about 0.07 eV (mean unsigned error = 0.05 eV) at the B3LYP/6-31 + G(d,p) level and larger errors with HF or MP2 methods or using Koopmans' Theorem. Comparison of gas-phase free energies with solution-phase reduction potentials provides a measure of solvation energy differences between the radical anion and neutral PAH. A simple Born-charging model approximates the solvation effects on the radical anions, leading to a good correlation with experimental solvation energy differences. This is used to estimate unknown or questionable EAs from reduction potentials. Two independent methods are used to predict DeltaGo(a,298K) values: (1) based upon DFT methods, or (2) based upon reduction potentials and the Born model. They suggest reassignments or a resolution of conflicting experimental EAs for nearly one-half (17 of 38) of the PAH molecules for which experimental EAs have been reported. For the antiaromatic molecules, 1,3,5-tri-tert-butylpentalene and the dithia-substituted cyclobutadiene 1, the reduction potentials lead to estimated EAs close to those expected from DFT calculations and provide a basis for the prediction of the EAs and reduction potentials of pentalene and cyclobutadiene. The Born model has been used to relate the electrostatic solvation energies of PAH and hydrocarbon radical anions, and spherical halide anions, alkali metal cations, and ammonium ions to effective ionic radii from DFT electron-density envelopes. The Born model used for PAHs has been successfully extended here to quantitatively explain the solvation energy of the C60 radical anion.
Ab initio calculations employing electron propagator theory and many-body perturbation theory show that
the benzoate anion is a superhalide with an electron detachment energy in excess of 4.4 eV. Final states
associated with vertical electron detachment energies of the benzoate anion are reordered by correlation effects,
and the holes associated with the lowest neutral states thereby have O-centered σ character instead of ring-centered π character. Geometry optimizations on the dianions produced by attaching two carboxylate groups
to the benzene ring arrive at planar structures for the para and meta isomers, but in the ortho isomer, a C
2
structure with twisted OCO groups is found. The most stable isomer is para, and the least stable is ortho. The
lowest vertical detachment energies are at least 1.4 eV for the para and meta isomers, but the estimate for the
ortho isomer is 0.8 eV. Corresponding Dyson orbitals exhibit ring-centered π character. Attempts to find
bound trianions with three carboxylate groups failed. In fluorinated compounds, the carboxylate groups rotate
so that they are perpendicular to the ring planes. These compounds possess higher electron binding energies.
The associated Dyson orbitals are delocalized over the ring, F, and carboxylate regions, and antibonding
phase relationships are obtained between ring π and substituent lobes.
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