Rearrangement Pathways of Arylperoxy Radicals. I. The Azabenzenes

Abstract

The potential energy surfaces for the reaction of pyridinyl radicals with O 2 have been studied using the B3LYP method. The initial production of the pyridinylperoxy radical followed by either simple decomposition or rearrangement to yield the intermediates (pyridinyloxy, dioxiranylpyridinyl, or dioxetanylpyridinyl radicals) has been explored. Transition-state structures for most of the steps are presented as well as relative free energies over a range of temperatures from 298 to 2000 K. The energetics of the analogous intermediates for the reaction of O 2 and other azabenzene radicals derived from pyridazine, pyrimidine, and pyrazine are also provided. O 2 dissociation from the arylperoxy radical is preferred rather than the loss of O atom to generate the corresponding aryloxy radical, and this preference is contrary to phenylperoxy radical decomposition. However, the formation of a dioxiranyl radical intermediate is the most accessible intermediate from the peroxy precursor at temperatures e500 K. Dioxetanyl intermediates are less favored but may provide a route to NO x generation from nitrogen substitution in aromatic fuels.

A Mechanistic Study of the Reactions of H, O (3P), and OH with Monocyclic Aromatic Hydrocarbons by Density Functional Theory

“…81 The oxidative decomposition of the aromatic radicals formed by the H-atom abstraction channel of relevance to hightemperature combustion chemistry has been the focus of several recent papers. 16,17,[82][83][84] During the review process, we became aware of a new hybrid HF-DFT method, the MPW1K formalism, which has been shown to improve the calculation of barrier heights for reactions involving smaller systems by a factor of 3 over the B3LYP method. To test if this technique would provide better agreement with experiment than the B3LYP method for the reactions studied in this paper, we employed the MPW1K/6-31+G(d,p) method to calculate the barriers for the radical addition and H-atom abstraction reactions of benzene.…”

“…The subsequent reaction pathways available following the initial addition of H, O, and OH to aromatic hydrocarbons of relevance to low-temperature atmospheric chemistry are the subject of a study that will be reported in a separate paper ,,− …”

Identification and Chemistry of Phenylnitrene in Premixed Pyridine/Oxygen/Argon Flame with Tunable Synchrotron Photoionization

“…By analogy to the formation of benzene via cyclopentadienyl (C 5 H 5 ) and methyl [30][31][32], both of which are observed in the present work, PhN can be produced through the reaction of C 5 H 5 and CN, as shown in formula (1). Fadden et al pointed out that the phenoxy radical may be formed from the reaction of C 6 H 5 and O 2 [33]. In the same way, PhN can be generated via the addition N 2 to C 6 H 5 .…”

Formation of Amino Acid Precursors in the Interstellar Medium. A DFT Study of Some Gas-Phase Reactions Starting with Methylenimine

“…Laboratory simulation of the formation and reactions of organic molecules in the interstellar medium is a difficult task. On the other hand, during the last three years there is a rapidly growing interest for the use of the quantum chemical ab initio and density functional theory (DFT) methods to study chemical mechanisms and energetics of interstellar organic reactions, mainly in the gas phase. − While many researches in the field try to employ the true electron correlation models (for example 11-14a,15-18,23-26 ), the use of the B3LYP hybrid functional becomes more and more frequently reported. ,,,, Besides the interstellar chemistry, this method was used in the studies of many other organic reactions − (some of them involving gaseous amino acids and related compounds 51,55,58 ). The reason for this growing popularity can be understood from the reported comparison of B3LYP to much more expensive methods: in many cases the DFT results (geometries and energies) were noted to be in a remarkably good agreement with those obtained by the higher-level theories CISD, CCSD, CASSCF 14a,17,28-31,58 and G2 23,30,59 or demonstrated even the top performance approaching, as the ideal case, to experimental data. 14b-e,,,,,,…”