Density Functional Study of the High-Temperature Oxidation of o-, m- and p-Xylyl Radicals

Abstract

Theoretical calculations at the CBS-QB3 level of theory have been performed to investigate the potential energy surface for the reaction of o-, m- and p-xylyl with molecular oxygen. The differences of the relative potential energies for the products and the transition states of o-, m- and p-xylyl with molecular oxygen were found to be within 8.5 kJ/mol at the CBS-QB3 level of theory. Although the reaction of m- and p-xylyl radicals with molecular oxygen have the same reaction pathways and also the same reaction thermochemistry as that of benzyl radicals, the o-xylylperoxy radicals formed by the reaction of o-xylyl + O(2) had an additional intramolecular isomerization pathway to form the o-xylyl hydroperoxy radicals. The rate constants and the product branching ratios for the o-xylyl + O(2) and its subsequent reactions were evaluated by the RRKM and master equation analysis. Possible roles for these reaction pathways on the combustion of o-xylenes are discussed.

Theoretical considerations of secondary organic aerosol formation from H-abstraction of p-xylene

“…In daytime, the reaction of aromatic hydrocarbons with hydroxyl radicals is the major atmospheric loss process [14][15][16]. Several previous experimental [17][18][19] and theoretical [20][21][22][23][24][25][26] studies have unraveled the elementary reactions involved in aromatic oxidation.…”

An experimental and modeling study of shock tube and rapid compression machine ignition of n-butylbenzene/air mixtures

“…As described in our recent n-propylbenzene paper [44], the addition reactions of the benzyl radical to molecular oxygen, an important step in the low temperature mechanisms of alkylbenzenes in general, have been derived by fitting over the temperature range of interest (600-900 K) the reaction rates that have been theoretically calculated by Murakami et al [46] for the xylyl + O 2 system. The reaction rate for the concerted elimination of HȮ 2 radical from the alkylperoxy species have been derived from Altarawneh et al [47], as in [44].…”

Density functional study of the phenylethyl + O2 reaction: Kinetic analysis for the low‐temperature autoignition of ethylbenzenes

“…Figure 5 summarizes the calculated optimized geometries of these structures at the B3LYP/6-311G(2d, d, p) level of theory. It was revealed that the transition state structure TS6a for the dissociation of the cyclic O 2 intermediates 5a resembled with that for the concerted dissociation of the cyclic O 2 intermediate of the benzylperoxy radicals [16] as well as that of o-xylylperoxy radicals [5]. Table II Table II are also summarized in Figure 6.…”

“…As there were no distinct transition states for such backward reactions, variable transition state for each temperature was determined by searching the geometries that give maximum Gibbs free energies at each temperature. Because the DFT was one of the most accurate and relatively low-cost level of theories that could predict the accurate potential energy profiles of benzyl þ O 2 [16] and xylyl þ O 2 [5] reaction systems, and furthermore Senosiain et al [21] and Silva et al [22] also succeeded in calculating the minimum energy profiles for the OH þ acetylene reaction and for the thermal decomposition of benzyl radical using the B3LYP method, respectively, we have applied the same theory to determine the variable transition state for the backward reactions of the phenylethylperoxy radicals to form phenylethyl þ O 2 . Figure 7 shows the potential energy profiles for the backward dissociation pathways of a-phenylethyl (C 6 H 5 CHCH 3 O 2 , 1a) þ O 2 and b-phenylethyl (C 6 H 5 CH 2 CH 2 O 2 , 1b) þ O 2 .…”

“…Later, Murakami et al [5] and Silva [6] independently investigated the reasons of such different ignition behaviors for these alkylbenzenes using the quantum chemical calculations and found that the intramolecular H-atom migration between the side chains of the phenylalkylperoxy radicals played the important roles in the autoignition for these alkylbenzenes. In other words, positions of the aromatic side chains controls the ignition features for the alkylbenzenes.…”