Theoretical calculation of intramolecular reactions in methylperoxyl and ethylperoxyl radicals

Abstract

Ab initio molecular orbital calculations on t h e intramolecular rearrangements of t h e methylperoxyl and ethylperoxyl radicals are reported, together with transition-state structures and vibration frequencies for t h e ethylperoxyl reactions. Estimated equilibrium constants for t h e formation of two methylperoxyl isomers, CH(OH), and CH,(OH)O, are also reported.

The C2H5 + O2 Reaction Mechanism: High-Level ab Initio Characterizations

“…This “strained” species has an imaginary frequency of 2145 i cm -1 and lies, as might be expected, 4.4 kcal mol -1 above the corresponding β-hydrogen isomerization barrier, TS2 , and 11.5 kcal mol -1 above reactants. M3 has only been examined theoretically in the work of Shen, Moise, and Pritchard, who predicted TS4 to lie 50.4 kcal mol -1 above 2 at the MP4/ 6-31G//MP2/6-31G level. Our results place TS4 at 41.8 kcal mol -1 above 2 , over 8 kcal mol -1 lower than that of Shen et al and consistent with an expected barrier lowering usually seen with improved correlation treatments.…”

“…He also placed this barrier slightly above (about 1.5 kcal mol -1 ) that for hydroperoxyethyl decomposition into oxirane + • OH. In contrast, Shen, Moise, and Pritchard 73 found the barrier to be slightly below that for decomposition into oxirane + • OH, by 3.3 kcal mol -1 at the UMP4//6-31G// UMP2/6-31G level. Shen et al also placed the R-hydrogen transfer barrier of ethylperoxy at 9.1 kcal mol -1 above the β-hydrogen transfer barrier (cf.…”

“…In summary, by 1997 the theoretical studies of QGS and IXAS seemed to favor concerted elimination of HO 2 • from the ethylperoxy radical, rather than ethylperoxy β-hydrogen transfer, in contrast to the conclusions of most experimental work, though not necessarily at variance with the observations. Furthermore, the work of Pritchard et al 73 and Green 72 indicated that the barrier for decomposition of • CH 2 CH 2 OOH into ethylene is small (around 10 kcal mol -1 above products) but competitive with that for decomposition into oxirane, thus leaving the predominance of ethylene formation unexplained if M4 is operative. However, in nearly every theoretical study, questions as to the reliability of the theoretical results may be raised due to either spin contamination in unrestricted wave functions, multireference character in the electronic structure, or intricacies arising from the low-lying excited-state surface.…”

A theoretical analysis of the reaction between ethyl and molecular oxygen

“…[15][16][17]. and references cited therein) with methods ranging from density functional theory to more traditional MPn, coupled cluster, and configuration interaction methods.…”

A theoretical study on the reaction mechanism of O2 with C4H9• radical

“…However, because of the difficulty in producing these transient species, often limited information is available under well-defined experimental conditions. Theoretical studies on the reaction of hydrocarbon radicals are also quite scarce except for some calculations on a few simple systems, among which the reactions of allyl radical (C 3 H 5 •) [18][19][20][21][22][23][24] and ethane radical (C 2 H 5 •) [25][26][27][28][29][30][31][32][33][34][35][36] have attracted more attentions than others. Estupiñán et al studied the reactions of C 2 H 5 , n-C 3 H 7 , and i-C 3 H 7 radicals with O 2 using the technique of laser photolysis/long-path frequency-modulation spectroscopy and ab initio method [37].…”