title: Thermochemistry of acetonyl and related radicals.
abstract: 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 (CH(3)COC*H2). In turn, this was used to determine formation enthalpies of 2-oxoethyl or formylmethyl (C*H(2)CHO), 2-oxobutyl (C*H(2)COC(2)H(5)), 1-methyl-2-oxopropyl or methylacetonyl (C*H(CH(3))COCH(3)), 1-methyl-2-oxobutyl (C*H(CH(3))COC(2)H(5)), and 3-oxopentyl (C*H(2)CH2COC(2)H(5)). Our computed standard enthalpy of formation of -34.9 +/- 1.9 kJ mol-1 and a resonance stabilization energy of approximately 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 DeltaH(f)o (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 DeltaH(f)o the 2-oxoethyl radical to +13 +/- 2 kJ mol(-1).
authors.affiliation: Chemistry Department & Environmental Change Institute, National University of Ireland, Galway, Ireland.
authors.forename: Ahmed M
authors.initials: AM
authors.lastname: El-Nahas
authors.forename: Joseph W
authors.initials: JW
authors.lastname: Bozzelli
authors.forename: John M
authors.initials: JM
authors.lastname: Simmie
authors.forename: Maria V
authors.initials: MV
authors.lastname: Navarro
authors.forename: Grainne
authors.initials: G
authors.lastname: Black
authors.forename: Henry J
authors.initials: HJ
authors.lastname: Curran