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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Case of the Missing Isomer: Pathways for Molecular Elimination in the Photoinduced Decomposition of 1,1-Dibromoethane
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Case of the Missing Isomer: Pathways for Molecular Elimination in the Photoinduced Decomposition of 1,1-Dibromoethane

机译：缺少异构体的情况：1，1-二溴乙烷光诱导分解中的分子消除途径

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摘要

We report an experimental and computational study of the photodecomposition pathways of a prototypical gem-dihalide, 1,1-dibromoethane (1,1-EDB), in the condensed phase. Following photolysis of the matrix isolated parent compound in Ar at 5 K, photoproducts are observed corresponding to Br2 elimination (+ C_2H_4 or C_2H_2) and HBr elimination (+ vinyl bromide). The elimination products are observed in the matrix as complexes. In contrast to our recent studies of the photolysis of matrix isolated polyhalomethanes, no evidence for the iso-1,1-EDB species is found, although studies of the matrix isolated 1,1-dibromo-2,2,2-trifluoroethane analogue show that the isomer is the dominant photoproduct. These results are examined in the light of theoretical studies that have characterized in detail the 1,1-EDB potential energy surface (PES). For Br2 elimination, a pathway from the isomer on the singlet PES is found which involves a simultaneous Br_2 loss with 1,2- hydrogen shift; this pathway lies lower in energy than a concerted three-center elimination from the parent 1,1-EDB. For HBr elimination, our previous theoretical studies [Kalume, A.; George, L.; Cunningham, N.; Reid, S. A. Chem. Phys. Lett. 2013, 556, 35?38] have demonstrated the existence of concerted (single-step) and sequential pathways that involve coupled proton and electron transfer, with the sequential pathway involving the isomer as an intermediate. Here, more extensive computational results argue against a simple radical abstraction pathway for this process, and we compare experimental and computational results to prior results from the photolysis of the structural isomer, 1,2-EDB. These steady-state experiments set the stage for ultrafast studies of the dynamics of this system, which will be important in unraveling the complex photodecomposition pathways operative in condensed phases.
机译：我们报告了凝聚态的原型典型的二卤代甲烷1，1-二溴乙烷（1,1-EDB）的光解途径的实验和计算研究。在Ar在5 K下对基质分离的母体化合物进行光解后，观察到光产物对应于Br2消除（+ C_2H_4或C_2H_2）和HBr消除（+乙烯基溴）。在基质中观察到消除产物为络合物。与我们最近对基质分离的多卤代甲烷光解的研究相反，尽管对基质分离的1,1-二溴-2,2,2-三氟乙烷类似物的研究表明，没有发现iso-1,1-EDB物种的证据。异构体是主要的光产物。根据详细表征1,1-EDB势能面（PES）的理论研究检查了这些结果。为了消除Br 2，发现了来自单重态PES上异构体的途径，该途径涉及同时发生Br 2损失和1,2-氢转移。该途径的能量低于从母体1,1-EDB协同消除三中心的能量。对于消除HBr，我们以前的理论研究[Kalume，A .;乔治北卡罗来纳州坎宁安; Reid，S.A. Chem。物理来吧[2013，556，35？38]已证明存在涉及质子和电子转移耦合的协同（单步）和顺序路径，其中以异构体为中间体的顺序路径。在这里，更广泛的计算结果反对此过程的简单自由基提取途径，并且我们将实验和计算结果与结构异构体1,2-EDB光解的先前结果进行了比较。这些稳态实验为超快速研究该系统的动力学奠定了基础，这对于弄清在凝聚相中起作用的复杂光分解途径至关重要。

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