Abstract Cyclohexenes are important oxidation intermediates for cyclohexanes and precursors of aromatic hydrocarbons. 3-methylcyclohexene is one of important intermediate products of methylcyclohexane oxidation. In order to improve the understanding of oxidation for 3-methylcyclohexene, the decomposition pathways of 3-methylcyclohexene radical isomers were investigated using ab initio theoretical method. The molecular geometric structures of stationary points on the potential energy surfaces were optimized at B3LYP/6–311++G(d,p) level and then the single point energies were extrapolated using complete basis set (CBS) based on the results obtained using MP2 and QCISD(T) methods with basis sets of cc-pVDZ and cc-pVTZ. The reactivity of reaction channels are discussed with the energy barriers on potential energy surfaces. It is observed the decompositions of allylic radicals have clearly high barrier heights. The products of decomposition of 3-methylcyclohexene radicals are alkyl and alkenyl chain radicals via ring opening reactions, cyclic diolfins plus H atom via C–H bond fission, and cyclohexadienes plus methyl via side chain dissociation. Then it is shown that energies delivered with various quantum chemistry methods are of great similarity. Rate constants of major channels for all radicals were computed with information of stable and saddle points collected on the PESs. The high pressure limits of ring opening and dehydrogenation reactions are comparable for all alkyl radicals, while the other two allylic radicals possess much distinguished values. Finally, the pressure-dependent rate constants are computed based on RRKM/ME theory. The rate constants of ring opening reactions are compared with literature data for similar molecules.

中文翻译：

---

3-甲基环己烯自由基的分解：其机理发展的开始

摘要 环己烯是环己烷的重要氧化中间体和芳烃的前体。3-甲基环己烯是甲基环己烷氧化的重要中间产物之一。为了加深对3-甲基环己烯氧化的理解，采用从头算理论方法研究了3-甲基环己烯自由基异构体的分解途径。在 B3LYP/6–311++G(d,p) 水平优化势能面上驻点的分子几何结构，然后基于使用获得的结果使用完全基组 (CBS) 外推单点能量使用 cc-pVDZ 和 cc-pVTZ 基组的 MP2 和 QCISD(T) 方法。反应通道的反应性与势能面上的能垒讨论。观察到烯丙基的分解具有明显高的势垒高度。3-甲基环己烯自由基的分解产物是通过开环反应生成的烷基和烯基链自由基，通过C-H键裂变生成环状二醇加H原子，通过侧链解离生成环己二烯加甲基。然后表明各种量子化学方法传递的能量具有很大的相似性。使用在 PES 上收集的稳定点和鞍点信息计算所有自由基的主要通道的速率常数。所有烷基自由基的开环和脱氢反应的高压极限是可比的，而其他两个烯丙基自由基具有许多显着的价值。最后，基于 RRKM/ME 理论计算压力相关的速率常数。