Thermochemistry of Acetonyl and Related Radicals

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2006-12, Vol.110 (50), p.13618-13623
• Main Authors: El-Nahas, Ahmed M, Bozzelli, Joseph W, Simmie, John M, Navarro, Maria V, Black, Gráinne, Curran, Henry J
• Format: Article
• Language: English
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp065003y

Density functional and ab initio calculations at CBS-QB3 levels of theory were employed with a series of isodesmic reactions to determine the thermochemistry of the 2-oxopropyl or acetonyl radical (CH3COC•H2). In turn, this was used to determine formation enthalpies of 2-oxoethyl or formylmethyl (C•H2CHO), 2-oxobutyl (C•H2COC2H5), 1-methyl-2-oxopropyl or methylacetonyl (C•H(CH3)COCH3), 1-methyl-2-oxobutyl (C•H(CH3)COC2H5), and 3-oxopentyl (C•H2CH2COC2H5). Our computed standard enthalpy of formation of −34.9 ± 1.9 kJ mol-1 and a resonance stabilization energy of ∼22 kJ mol-1 for acetonyl are in good agreement with recent re-determinations, which have indicated a substantial lowering in the long-established value for Δ (298.15 K). A bond dissociation energy of 401 kJ mol-1 is suggested for the C−H bond in acetone with consistent values for the others. The calculations support the enthalpy of formation of acetaldehyde obtained from combustion experiments of −166.1 kJ mol-1 rather than the figure of −170.7 kJ mol-1 extracted from enthalpies of reduction and, in addition, serve to reduce the uncertainty in Δ of the 2-oxoethyl radical to +13 ± 2 kJ mol-1.