Kinetic Study on Reactions of 1- and 2-Methylvinoxy Radicals with O₂

Abstract

The reactions of 1-and 2-methylvinoxy radicals with O 2 have been studied by laser-induced fluorescence coupled with pulsed laser photolysis of precursor molecules at room temperature (298 ( 5 K). The rate constants for both reactions showed typical falloff pressure dependence in the investigated pressure range (8-330 Torr, He buffer), which suggests the dominance of recombination processes to form peroxy radicals. From the Rice-Ramsperger-Kassel-Morcus fit to the experimental data, the limiting high-pressure rate constants were derived to be k ∞ (1-methylvinoxy + O 2 ) ) 9.8 × 10 -13 and k ∞ (2-methylvinoxy + O 2 ) ) 1.3 × 10 -12 cm 3 molecule -1 s -1 , which are 5-7 times larger than that for the reaction of a nonsubstituted vinoxy radical. The influence of the methyl substituent effect and the resonance stabilization on the rate constants is discussed.

Estimation of rate coefficients and branching ratios for gas-phase reactions of OH with aliphatic organic compounds for use in automated mechanism construction

“…e Based on the average of rate coefficients reported by Bowry et al (1991) for a series of cyclopropyl-alkyl radicals, representing the value per relevant bond. f The values of k dec /k O 2 shown for the secondary and tertiary reagent radical (1) can be adjusted approximately for the effects of a substituent group, X, in cyclo-propyl-ĊH-X and cyclo-propyl-Ċ(R )-X, using the following temperature-independent factors: i F dec/O 2 (-OH) = 0.6, based on rate coefficients reported for reactions of O 2 with the α-hydroxyalkyl radicals, CH 3Ċ HOH (http://iupac.pole-ether.fr/; last access: September 2017), C 2 H 5Ċ HOH (Miyoshi et al, 1990) and CH 3Ċ (OH)CH 3 (Miyoshi et al, 1990); (ii) F dec/O 2 (-C(=O)-) = 7.0, based on rate coefficients reported for reactions of O 2 with the β-oxoalkyl/vinoxy radicals CH 3 C(=O)ĊH 2 (http://iupac.pole-ether.fr/; last access: September 2017) and CH 3Ċ HC(=O)H (Oguchi et al, 2001); (iii) F dec/O 2 (-C(OH)<) = 1.7, based on rate coefficients reported for reactions of O 2 with the β-hydroxyalkyl radicals CH 3Ċ HCH 2 OH and CH 3 CH(OH)ĊH 2 (Miyoshi et al, 1990); (iv) F dec/O 2 (=O) = 4.5, based on rate coefficient reported for reaction of O 2 with CH 3Ċ O (http://iupac.pole-ether.fr/; last access: September 2017); and (v) F dec/O 2 (=C<) = 0.9, based on rate coefficient reported for reaction of O 2 with CH 2 =ĊH (Matsugi and Miyoshi, 2014). For other substituents, F dec/O 2 = 1.0 is assumed, in the absence of data.…”

Rate constant for the reaction of CH3C(O)CH2 radical with HBr and its thermochemical implication

“…The acetonyl radical contains a partially delocalized electronic structure which may be viewed as a “resonance” between the “alkyl form” • CH 2 C(O)CH 3 and the “alkoxyl form” CH 2 C(O • )CH 3 mezomeric structures. Recent experimental and theoretical studies 1–3 have shown the acetonyl radical to behave like an alkyl radical and not like an alkoxyl radical in its elementary reactions with O 2 , NO, NO 2 , and H atoms. In order to further examine structure–activity relations, the rate constant obtained for reaction (1) in the present work has been compared with those for selected radical + HBr reactions from the literature in Table II.…”

“…Recent interest in the kinetic behavior 1–3 and thermochemical properties 4,5 of the acetonyl radical, CH 3 C(O)CH 2 , stems in a great part from the recognition of the important role this radical plays in the chemistry of the atmosphere 6,7. Acetonyl is formed in OH hydrogen abstraction reaction from acetone 7, CH 3 C(O)CH 3 , which has recently been found one of the most abundant partially oxidized organics in the atmosphere 8.…”

Is either direct photolysis or photocatalysed H-shift of peroxyl radicals a competitive pathway in the troposphere?

“…Peroxyl radicals (RO _ O), usually formed by the addition of O 2 to carbon-centred radicals, are crucial intermediates in both atmospheric oxidation and combustion. Compared to alkoxy and alkyl radicals, peroxyl radicals are relatively long-lived, as their main sink reactions involve low-concentration radicals such as NO, HO _ O or other RO _ O [7][8][9][10]. Especially, the latter reaction mechanism has recently received much attention as it may lead (via intersystem crossings) to the formation of low-volatility ROOR 'dimers' crucial for the growth of atmospheric aerosol [10].…”

“…With the exception of NO 2 , the photolysis of radical species is seldom considered in atmospheric chemistry, mainly due to the very short lifetimes of most atmospherically relevant classes of radicals. For example, most alkoxy (R ) and alkyl ( ) radicals typically have atmospheric lifetimes around or below 10 −4 and 10 −8 s, respectively [ 6 – 8 ]. Even if photolysis of these species were reasonably fast, it would thus be unable to compete with other chemical loss channels [ 1 , 5 , 6 ].…”