Computational Study of the Reaction Mechanism of the Methylperoxy Self-Reaction

Abstract

To provide insight on the reaction mechanism of the methyperoxy (CH(3)O(2)•) self-reaction, stationary points on both the spin-singlet and the spin-triplet potential energy surfaces of 2(CH(3)O(2)•) have been searched at the B3LYP/6-311++G(2df,2p) level. The relative energies, enthalpies, and free energies of these stationary points are calculated using CCSD(T)/cc-pVTZ. Our theoretical results indicate that reactions on a spin-triplet potential energy surface are kinetically unfavorable due to high free energy barriers, while they are more complicated on the spin-singlet surface. CH(3)OOCH(3) + O(2)(1) can be produced directly from 2(CH(3)O(2)•), while in other channels, three spin-singlet chain-structure intermediates are first formed and subsequently dissociated to produce different products. Besides the dominant channels producing 2CH(3)O• + O(2) and CH(3)OH + CH(2)O + O(2) as determined before, the channels leading to CH(3)OOOH + CH(2)O and CH(3)O• + CH(2)O + HO(2)• are also energetically favorable in the self-reaction of CH(3)O(2)• especially at low temperature according to our results.

Computed Regioselectivity and Conjectured Biological Activity of Ene Reactions of Singlet Oxygen with the Natural Product Hyperforin

“…A 38.8 kcal mol À1 saddle point (TS4) connects 2 CH 3 O 2 • with CH 3 OH + formaldehyde + 1 O 2 with a correction used of 3 O 2 + 22.5 kcal mol À1 (path D, Fig. 7), which is in reasonably good agreement with the CCSD(T)/cc-pVTZ// B3LYP/6-311++G(2df,2p) calculated barrier of 33.3 kcal mol À1 (46). Pathway E is also high in energy due to the formation of singlet oxygen, where a 63.4 kcal mol À1 saddle point (TS5) connects 2 CH 3 O 2 • with CH 3 OOCH 3 and 1 O 2 (path E, Fig.…”

“…These calculations are related to solvent‐accessible areas, which have an error of 1.6 Å 2 to 3.0 Å 2 . Previous CCSD(T)/cc‐pVTZ//B3LYP/6‐311++G(2df,2p) or CCSD(T)/cc‐pVTZ//B3LYP/6‐311G(2d,2p) studies were successful in computing reactions of methyl and ethyl peroxy radicals , respectively. Here, we have used B3LYP/D95** calculations which have performed well in predicting reaction enthalpies of peroxy radicals .…”

“…Previous CCSD(T)/cc‐pVTZ//B3LYP/6‐311++G(2df,2p) or CCSD(T)/cc‐pVTZ//B3LYP/6‐311G(2d,2p) studies were successful in computing reactions of methyl and ethyl peroxy radicals , respectively. Here, we have used B3LYP/D95** calculations which have performed well in predicting reaction enthalpies of peroxy radicals . The closed‐shell method of calculation was adopted because unrestricted calculations for transition states of Russell reaction could result in high spin contamination as found often in diradicals .…”

Intersystem Crossings Drive Atmospheric Gas-Phase Dimer Formation

“…Peroxy radical (RO2) recombination, RO2 + R'O2 → ROOR' + O2, provides a dimerization mechanism that phenomenologically fits the observational gas-phase data well. 11 However, experiments 12,13, and computational studies 14,15 on simple peroxyradicals following the established 60-year old Russell mechanism for RO2 self-reactions, 16 suggest that this channel is negligible compared to the competing channels forming RO + R'O + O2 or R-H=O + R'OH + O2. The Russell mechanism postulates that RO2 + R'O2 reactions first lead to a metastable RO4R' tetroxide intermediate, which then undergoes different types of rearrangements to yield the three product channels: RO + R'O + O2, R-H=O + R'OH + O2 or ROOR' + O2, with the latter believed until recently to only occur in the condensed phase.…”

Theoretical studies on the mechanism and kinetic for CH3CH2O + HO2 and CH3CHOH + HO2 reactions

“…This indicates that the CCSD wave functions are reliable in this study. Finally, the kinetic properties of the system were calculated using conventional transition state theory with the Wigner tunneling correction in Polyrate 8.2 program . As described in Equation , the part of reactions began with the formation of a pre‐reactive complex before progressing through the transition state.…”