Theoretical study of the energetic and possible intermediates of the CH3CH2O2 self‐reaction

Abstract By means of ab initio and density functional theory methods we have studied the geometry and electronic structure of the ethyl peroxyl radical, CH3CH2O2, and of the tetraoxide intermediates, CH3CH2O4CH2CH3, involved in the self‐reaction of this radical. These kinds of reactions may occur in the troposphere and, depending on the structure of the intermediates, the following pathways are originated: (I) 2CH3CH2O2 → 2CH3CH2O + O2, (II) 2CH3CH2O2 → CH3CH2OH + CH3CHO + O2, and (III) 2CH3CH2O2 → CH3CH2O2CH2CH3 + O2. The energetic of these three reactions was also addressed. With the aid of the Gaussian 98 package, full geometry optimizations, electronic structure, vibrational frequencies, and total energies were determined for reactives, intermediates, and products of each pathway. Calculations, of the all‐electron type, were done at the Hartree–Fock (HF), MP2, and B3LYP levels of theory using 6‐311G(2d,2p) orbital basis sets. It was found that the B3LYP results, for the enthalpy of the reactions, ΔHr, are in better agreement with the experiment than the HF and PMP2 estimates. Indeed, the ΔHr for paths I and II, including zero‐point energies, are +2.3 and −80.2 kcal/mol, respectively, which compares well with the experimental values: +5.5 and −82.0 kcal/mol. Our prediction for ΔHr of path III is −29.7 kcal/mol. Moreover, three intermediates, A, B, and C, of different geometry and energy were found. The structure of each intermediate is closely connected with the products obtained in each reaction path, as determined experimentally. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004