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Theoretical Study of the Energetic and Possible Intermediates of the CH<inf>3</inf>CH<inf>2</inf>O<inf>2</inf> 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) 2CH3CH 2O2 → CH3CH2OH + CH 3CHO + O2, and (III) 2CH3CH2O 2 → CH3CH2O2CH 2CH3 + 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 pbkp_rediction 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.