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).

Kinetics and mechanism of the reaction of acetonyl radical, CH3C(O)CH2, with Br2

“…Acetonyl has a partially delocalized electronic structure that may be portrayed by the limiting "alkyl", •CH 2 C(=O)CH 3 , and "alkoxyl", CH 2 =C(-O•)CH 3 , resonance structures [17], [18].…”

“…The long established standard enthalpy of formation of acetonyl, ∆ f H°2 98 (CH 3 C(O)CH 2 ) = -23 ± 8 kJ mol -1 , was proposed by King et al by kinetic study of the gas-phase bromination of acetone [5], while the recent reports converge to a value which is ~10 kJ mol -1 smaller (a thorough overview of the literature has been presented in [18]). The critically evaluated, recommended value is ∆ f H°2 98 (CH 3 C(O)CH 2 ) = -34 ± 3 kJ mol -1 [10].…”

“…Obviously, it does not follow from this analysis that the 'old' enthalpy value should be preferred. In fact, currently there has been a clear consensus in favor of the lower enthalpy of formation of acetonyl [10], [18] as noted. Some systematic errors may have occurred in the experiments of King and co-workers [5], or some of the assumptions they made were not correct to evaluating the experimental data.…”

Thermochemical properties for n‐propyl, iso‐propyl, and tert‐butyl nitroalkanes, alkyl nitrites, and their carbon‐centered radicals

“…Since enthalpies of formation of the three reference compounds (values above in bold) are well established [40] in the literature, the heat of reaction, rxn H…”

Experimental and Modeling Studies of the Oxidation of Surrogate Bio-Aviation Fuels

“…Mixtures of 80% kerosene and 20% FAMEs were widely considered as a possible option to be used in aviation; however, because of the physical properties of FAMEs and their levels of metallic contaminants, this is no longer an acceptable option and, in practice, only synthetic Fischer Tropsch derived fuels have a future as a kerosene replacement. Few studies have investigated the oxidation chemistry of oxygenated compounds, such as acetic and propanoic acids [3,4], followed by detailed chemical reaction mechanisms for small fatty acid methyl esters as biofuel surrogates [5][6][7][8][9][10]. Dagaut et al [11] developed a model for the combustion of biokerosene, basing it on previous studies [12], which showed that the biofuel portion (typically rapeseed methyl esters (RME)) could be well represented by hexadecane.…”