Thermochemistry and kinetics of acetonylperoxy radical isomerisation and decomposition: a quantum chemistry and CVT/SCT approach

Abstract

CBS-QB3 calculations have been used to determine thermochemical and kinetic parameters of the isomerisation and decomposition reactions of the acetonylperoxy radical, CH3C(O)CH2OO* , which has been formed via the reaction of acetonyl radical with O2 leading to the formation of an energised peroxy adduct with a calculated well depth of near 111 kJ mol(-1). This species can undergo subsequent 1,5 and 1,3 H-shifts to give the primary and secondary radicals: C*H2C(O)CH2OOH and CH3C(O)C*HOOH, respectively, or rearrange to give a 3-methyl-1,2-dioxetan-3-yloxy radical. Rate constants for isomerisation and subsequent decomposition have been estimated using canonical variational transition state theory with small curvature tunneling cvt/sct. The variational effect for the isomerisation channels is only moderate but the tunneling correction is significant at temperatures up to 1000 K; the formation of a primary radical by a 1,5-shift is the main reaction channel and the competition with the secondary one starts only at around 1500 K. The fate of the primary acetonylhydroperoxy radical is predominantly to form oxetan-3-one while the ketene and 1-oxy-3-hydroxyacetonyl radical channels only compete with the formation of oxetan-3-one at temperatures >1200 K. In addition, consistent and reliable enthalpies of formation have been computed for the molecules acetonylhydroperoxide, 1,3-dihydroxyacetone, methylglyoxal and cyclobutanone, and for some related radicals.

Acetonyl Peroxy and Hydro Peroxy Self- and Cross-Reactions: Kinetics, Mechanism, and Chaperone Enhancement from the Perspective of the Hydroxyl Radical Product

“…The initial reaction is a 1,5 H-shift from the methyl group with an MC-TST calculated rate coefficient of 5.9 × 10 -6 s -1 . The high barrier resulting in low rate coefficient for this reaction is in agreement with previous studies 17, [72][73][74][75] and has been ascribed to the strain in the TS induced by the sp 2 -hybridized carbon atom reducing the flexibility. 72 This means that the 1,5 H-shift is negligible from the thermalized peroxy radical under all relevant time scales and any possible OH-recycling from reactions following this Hshift thus relies on it occurring via excess energy from the O2-addition to the CH3C(O)CH2O2…”

Vibrational spectra, normal coordinate analysis, and structure of keto form of acetylacetone. A DFT approach

“…The bulk solvent effect is described by the polarizable continuum method (PCM) [44,45] at 298.15 K and 1.0 atm by performing SCRF calculations at the B3LYP/6-311++G(d,p) level. It has been shown that the thermodynamics results obtained with the CBS-QB3 [46] and B2PLYP [47] levels are comparable with the experimental data [48][49][50]. Therefore, the relative stability of considered tautomers and the equilibrium constants between these tautomers in the gas phase as well as in the solutions are calculated at the CBS-QB3 and B2PLYP/6-31+G(2d,p) levels.…”

Computational Treatments of Peroxy Radicals in Combustion and Atmospheric Reactions

“…For the 1-methylvinoxy (or acetonyl) radical, there is again a remarkable agreement between the experimental estimate 88 of the O 2 addition barrier, −0.60 ± 0.05 kcal mol −1 , and the CBS-QB3 barrier of −0.6 kcal mol −1 reported by El-Nahas and coworkers 38 and newly computed by the author of this review using Gaussian 09 52 . (Again, the barrier previously reported by Kuwata and coworkers 26 of 2.4 kcal mol −1 was based on a faulty implementation of CBS-QB3 in Gaussian 98 71 .)…”

“…El-Nahas and coworkers 38 note that the negative CBS-QB3 barrier implies the existence of a prereactive complex between the 1-methylvinoxy and the O 2 , but searches of the potential energy surface with the B3LYP/6-311G(d,p) model chemistry revealed no such minimum. An estimate of the reaction barrier based on a potential energy scan using the BB1K/cc-pVTZ model chemistry gives a value of 3.5 kcal mol −1 50 , and 298 K activation enthalpies using B3LYP are between 2.0 and 2.4 kcal mol −1 38, 49 .…”