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首页> 外文期刊>Computational & theoretical chemistry >Inquiry of the reaction paths in thermal retro-Diels-Alder reactions in the gas phase: Theoretical study on the concerted and stepwise elimination mechanisms of cyclohexenes
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Inquiry of the reaction paths in thermal retro-Diels-Alder reactions in the gas phase: Theoretical study on the concerted and stepwise elimination mechanisms of cyclohexenes

机译：气相热Diels-Alder逆反应中反应路径的探索：环己烯协同和逐步消除机理的理论研究

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摘要

The mechanisms of the thermal decomposition of cyclohexene (CH), 4-methylcyclohexene (4MCH) and 4-vinyl cyclohexene (4VCH) in the gas-phase were studied by means of electronic structure calculations using perturbation MP2 and Density Functional Theory (DFT) methods. Molecular and diradical reaction pathways were calculated. In the case of the 4-susbstituted cyclohexenes two diradical processes were considered. DPI' functionals, including a PT2 correction to the correlation energy, gave reasonable results for all reaction paths considered. Calculated parameters obtained with B2PLYP/6-31+G(d,p) are in good agreement with those reported in Tsang's experimental study. Evaluated kinetic parameters indicate that CH, 4MCH, and 4V.CH should follow the concerted molecular reaction pathway. However, it is possible that a fraction of the reactant molecules could overcome the energy barrier for the radical pathway, because of the high temperatures employed in the experimental conditions. The presence of methyl group in 4MCH slightly favors the breaking of C3-C4 bond. The effect of vinyl group is more dramatic, consisted with a resonance effect stabilizing C3 throughout the bond breaking process. NBO charges suggest these processes are discretely polar, since there are slight variations in the electron density along the reaction coordinates. The analysis of the evolution percentages obtained from bond indexes suggests that these reactions are non-synchronous. (C) 2015 Elsevier B.V. All rights reserved.
机译：利用扰动MP2和密度泛函理论（DFT）方法，通过电子结构计算，研究了环己烯（CH），4-甲基环己烯（4MCH）和4-乙烯基环己烯（4VCH）在气相中的热分解机理。 。计算了分子和自由基反应途径。在4-取代的环己烯的情况下，考虑了两个双自由基过程。 DPI的功能（包括对相关能量的PT2校正）为所有考虑的反应路径提供了合理的结果。用B2PLYP / 6-31 + G（d，p）获得的计算参数与曾荫权的实验研究报告的参数非常吻合。评估的动力学参数表明，CH，4MCH和4V.CH应该遵循一致的分子反应途径。但是，由于在实验条件下采用了高温，因此一部分反应物分子可能会克服自由基途径的能垒。 4MCH中甲基的存在稍微有利于C3-C4键的断裂。乙烯基的作用更为显着，包括在整个键断裂过程中稳定C3的共振效应。 NBO电荷表明这些过程是离散的极性，因为沿着反应坐标的电子密度略有变化。从键指数获得的演化百分比的分析表明，这些反应是不同步的。 （C）2015 Elsevier B.V.保留所有权利。

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