Thermochemical properties from G3MP2B3 calculations, Set‐2: Free radicals with special consideration of CH2CHC•CH2, cyclo−•C5H5, •CH2OOH, HO•CO, and HC(O)O•

Abstract

AbstractAfter a set of 32 free radicals was presented (Int J Chem Kin 34, 550–560, 2002), an additional 60 free radicals (Set‐2) were studied and characterized by energy minimum structures, harmonic vibrational wave numbers ωe, moments of inertia IA, IB, and IC, heat capacities Cop(T), standard entropies So(T), thermal energy contents Ho(T) − Ho(0), and standard enthalpies of formation ΔfHo(T) at the G3MP2B3 level of theory. Thermodynamic functions at T = 298.15 K are presented and compared with recent experimental values where these are available. The mean absolute deviation between calculated and experimental ΔfHo(298.15) values by the previous set of 32 radicals is 3.91 kJ mol−1. For the sake of comparison, only 49 species out of the 60 radicals of Set‐2 are characterized by experimental enthalpies of formation, and the corresponding mean absolute deviation between calculated and experimental ΔfHo(298.15) values is 8.96 kJ mol−1. This situation is cause for demand of more and also more accurate experimental values. In addition to the above properties, parent molecules of a large set of the respective radicals are calculated to obtain bond dissociation energies Do(298.15). Radical stabilization owing to resonance is discussed using the complete sets of total atomic spin densities ρ as a support. In particular, a short review about recent developments of the first‐order Jahn–Teller radical c‐C5H5• is presented. In addition, radicals with negative bond energies are described, such as •CH2OOH where the reaction path to CH2O + HO• has been calculated, as well as radicals which have two different parent molecules, for example CNO•. For the reaction HO• + CO → H• + CO2, two reaction paths are characterized by a total of 14 stationary points where the intermediate radicals HO•CO and HC(O)O• are involved. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 661–686, 2004