Sirjean B, Glaude P A, Ruiz-Lòpez M F, Fournet R
Département de Chimie Physique des Réactions, CNRS, Nancy-Université, 1 rue Grandville, BP 20451, 54001 Nancy Cedex, France.
J Phys Chem A. 2009 Jun 25;113(25):6924-35. doi: 10.1021/jp901492e.
Reactions of alkyl radicals with oxygen are key reactions in the low-temperature oxidation of hydrocarbons, but they have not been extensively studied yet in the case of cycloalkanes. Isomerizations of cycloalkylperoxy radicals and formation of cyclic ethers are especially important. In the present work, a theoretical study of the gas-phase reactions of cyclopentylperoxy and cyclohexylperoxy radicals has been carried out by means of quantum chemical calculations at the CBS-QB3 level. Computations on cyclopentylperoxy decomposition pathways are reported here for the first time. Thermochemical data have been obtained by means of isodesmic reactions, and the contribution of hindered rotors has been explicitly taken into account. Transition state theory has been used to calculate rate constants for all the elementary reactions. Three-parameter Arrhenius expressions have been derived in the temperature range 300-1000 K. Tunneling effects have been accounted for in the case of H-atom transfers. Our results compare well with experimental data and previous calculations available in the literature. In particular, the predicted rate constants for processes involving cyclohexylperoxy radicals, which have been introduced in a reaction mechanism scheme proposed before, exhibit excellent agreement with experiments at low and intermediate temperatures.
烷基自由基与氧的反应是烃类低温氧化中的关键反应，但在环烷烃的情况下，这些反应尚未得到广泛研究。环烷基过氧自由基的异构化和环醚的形成尤为重要。在本工作中，通过CBS-QB3水平的量子化学计算，对环戊基过氧自由基和环己基过氧自由基的气相反应进行了理论研究。本文首次报道了环戊基过氧自由基分解途径的计算结果。通过等键反应获得了热化学数据，并明确考虑了受阻转子的贡献。过渡态理论已被用于计算所有基元反应的速率常数。在300-1000 K的温度范围内导出了三参数阿伦尼乌斯表达式。在氢原子转移的情况下考虑了隧道效应。我们的结果与实验数据以及文献中先前的计算结果吻合良好。特别是，在之前提出的反应机理方案中引入的涉及环己基过氧自由基的过程的预测速率常数，在低温和中温下与实验结果表现出极好的一致性。
