| Abstract
| - High-level ab initio molecular orbital calculationshave been carried out for the phenyl cation (1),thephenyl radical (2), and the phenyl anion (3).Our best estimate for the heat of formation(ΔHf 298) of the phenylradical is 340 kJ mol-1, corresponding to 476kJ mol-1 for the 298 K C−H bonddissociation energy in benzene.The calculated ΔHf 298 of the phenylanion is 224 kJ mol-1, leading to an electronaffinity for the phenyl radical of116 kJ mol-1, and a gas-phase acidity forbenzene of 1671 kJ mol-1. The groundstate of the phenyl cation is foundto be a singlet(1-1A1,ΔHf 298 = 1134 kJmol-1), with the triplet(1-3B1,ΔHf 298 = 1237 kJmol-1) lying significantlyhigher in energy (by 103 kJ mol-1). Theenergies of the1-1A1and1-3B1states of the phenyl cation at the phenylradical geometry are much closer, but1-1A1remains the energetically lowest electronic state.The essentiallyisoenergetic1-3A2and1-1A2states lie about 25 kJ mol-1 higher in energythan1-3B1,while 1-1B1is nearly 60 kJmol-1 higher in energy. The implicationsof these results with respect to recent spectroscopic studies of thephenylradical and the role of the triplet phenyl cation in the dissociationof benzene cation are discussed.
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