Thermochemical parameters of three C₂H₅O^• radicals derived from ethanol were reevaluated using coupled-cluster theory CCSD(T) calculations, with the aug-cc-pVnZ (n = D, T, Q) basis sets, that allow the CC energies to be extrapolated at the CBS limit. Theoretical results obtained for methanol and two CH₃O^• radicals were found to agree within ±0.5 kcal/mol with the experiment values. A set of consistent values was determined for ethanol and its radicals: (a) heats of formation (298 K) ΔH_f(C₂H₅OH) = −56.4 ± 0.8 kcal/mol (exptl: −56.21 ± 0.12 kcal/mol), ΔH_f(CH₃C^•HOH) = −13.1 ± 0.8 kcal/mol, ΔH_f(C^•H₂CH₂OH) = −6.2 ± 0.8 kcal/mol, and ΔH_f(CH₃CH₂O^•) = −2.7 ± 0.8 kcal/mol; (b) bond dissociation energies (BDEs) of ethanol (0 K) BDE(CH₃CHOH−H) = 93.9 ± 0.8 kcal/mol, BDE(CH₂CH₂OH−H) = 100.6 ± 0.8 kcal/mol, and BDE(CH₃CH₂O−H) = 104.5 ± 0.8 kcal/mol. The present results support the experimental ionization energies and electron affinities of the radicals, and appearance energy of (CH₃CHOH⁺) cation. β-C−C bond scission in the ethoxy radical, CH₃CH₂O^•, leading to the formation of C^•H₃ and CH₂O, is characterized by a C−C bond energy of 9.6 kcal/mol at 0 K, a zero-point-corrected energy barrier of E₀^‡ = 17.2 kcal/mol, an activation energy of E_a = 18.0 kcal/mol and a high-pressure thermal rate coefficient of k_∞(298 K) = 3.9 s^-1, including a tunneling correction. The latter value is in excellent agreement with the value of 5.2 s^-1 from the most recent experimental kinetic data. Using RRKM theory, we obtain a general rate expression of k(T,p) = 1.26 × 10⁹p^0.793 exp(−15.5/RT) s^-1 in the temperature range (T) from 198 to 1998 K and pressure range (p) from 0.1 to 8360.1 Torr with N₂ as the collision partners, where k(298 K, 760 Torr) = 2.7 s^-1, without tunneling and k = 3.2 s^-1 with the tunneling correction. Evidence is provided that heavy atom tunneling can play a role in the rate constant for β-C−C bond scission in alkoxy radicals.

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