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首页> 外文期刊>Chemistry: A European journal >Hydrogen migrations in alkylcycloalkyl radicals: Implications for chain-branching reactions in fuels
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Hydrogen migrations in alkylcycloalkyl radicals: Implications for chain-branching reactions in fuels

机译：氢在烷基环烷基中的迁移：对燃料中支链反应的影响

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A thorough understanding of the oxidation chemistry of cycloalkanes is integral to the development of alternative fuels and improving current fuel performance. An important class of reactions essential to this chemistry is the hydrogen migration; however, they have largely been omitted from the literature for cycloalkanes. The present work investigates all of the hydrogen migration reactions available to methylcyclopentane, ethylcyclopentane, methylcyclohexane, and ethylcyclohexane. The kinetic and thermodynamic parameters have been studied by a combination of computational methods and compared to their corresponding n-alkyl and methylalkyl counterparts to determine the effect that the cycloalkane ring has on these reactions. In particular, although the alkylcycloalkyl activation energies for the dominant 1,4, 1,5, and 1,6 H-migration are higher than in n-alkyl and methylalkyl radicals, because several of the rotors needed to form the transition state are locked into place as part of the cycloalkane ring, the A-factors are higher for the alkylcycloalkyl reactions, making the rates closer to the noncyclic systems, at higher temperatures. The results presented here suggest that the relative importance of each H-migration pathway differs from the trends predicted by either the n-alkyl or methylalkyl radical systems. Of particular interest is the observation that since the barrier height of the 1,4 H-migration is only 3-5 kcal mol~(-1) higher than the 1,5 H-migration in the methyl and ethylcycloalkyl radicals, compared to a difference of roughly 7 kcal mol~(-1) in similar reactions for both the n-alkyl and methylalkyl radicals, the 1,4 H-migrations in alkylcycloalkyl radicals will be more important in the overall mechanism than would be predicted based on the n-alkyl and methylalkyl radicals. These results have important combustion model implications, particularly for fuels with high cycloalkane content. Chain-branching reactions: Cyclo alkanes make up a significant portion of traditional fuels and are present in even higher concentrations in certain emergent fuel sources, such as oil-sands. High-level computational methods are used to investigate the combustion mechanism of methyl- and ethyl-substituted cyclopentane and cyclohexane molecules. Ethylcyclohexyl radicals can participate in multiple different H-migration reactions, which can lead to branching of the reaction mechanism (see figure).
机译：对环烷烃氧化化学的透彻了解对于开发替代燃料和改善当前燃料性能至关重要。该化学必不可少的重要一类反应是氢迁移。然而，它们在环烷烃的文献中已被大量省略。本工作研究了可用于甲基环戊烷，乙基环戊烷，甲基环己烷和乙基环己烷的所有氢迁移反应。通过组合计算方法研究了动力学和热力学参数，并将其与相应的正烷基和甲基烷基对应物进行比较，以确定环烷环对这些反应的影响。特别是，尽管占主导地位的1,4、1,5和1,6 H迁移的烷基环烷基活化能比正烷基和甲基烷基自由基中的高，但由于形成过渡态所需的几个转子被锁定，作为环烷环的一部分，在较高温度下，烷基环烷基反应的A因子较高，从而使速率更接近于非环状体系。此处给出的结果表明，每个H迁移途径的相对重要性都与正烷基或甲基烷基自由基系统预测的趋势不同。特别令人关注的是，与甲基和乙基环烷基相比，由于1,4 H-迁移的势垒高度仅比甲基和乙基环烷基中的1,5 H-迁移高3-5 kcal mol〜（-1）。对于正烷基和甲基烷基自由基，在类似反应中大约有7 kcal mol〜（-1）的差异，烷基环烷基自由基中的1,4 H迁移在整个机理中比基于n预测的更为重要。 -烷基和甲基烷基。这些结果对燃烧模型具有重要意义，特别是对于具有高环烷烃含量的燃料。链支化反应：环烷烃占传统燃料的很大一部分，并且在某些新兴的燃料源（例如油砂）中以更高的浓度存在。使用高级计算方法来研究甲基和乙基取代的环戊烷和环己烷分子的燃烧机理。乙基环己基自由基可以参与多个不同的H迁移反应，这可能导致反应机理分支（见图）。

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