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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Unimolecular HCl Elimination from 1,2-Dichloroethane: A Single Pulse Shock Tube and ab Initio Study
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Unimolecular HCl Elimination from 1,2-Dichloroethane: A Single Pulse Shock Tube and ab Initio Study

机译：从1,2-二氯乙烷中去除单分子HCl：单脉冲激波管和从头算研究

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摘要

Thermal decomposition of 1,2-dichloroethane (1,2-DCE) has been studied in the temperature range of 1050-1175 K behind reflected shock waves in a single pulse shock tube. The unimolecular elimination of HCl is found to be the major channel through which 1,2-DCE decomposes under these conditions. The rate constant for the unimolecular elimination of HCl from 1,2-dichloroethane is found to be 10~(13.98±0.80) exp(-57.8±2.0/RT) s~(-1), where the activation energy is given in kcal mol~(-1) and is very close to that value for CH_3CH_2Cl (EC). Ab initio (HF and MP2) and DFT calculations have been carried out to find the activation barrier and the structure of the transition state for this reaction channel from both EC and 1,2-DCE. The preexponential factors calculated at various levels of theory (HF/6-311++G**, MP2/6-311++G**, and B3LYP/6-311++G**) are (≈10~(15) s~(-1)) significantly larger than the experimental results. If the torsional mode in the ground state is treated as free internal rotation the preexponential factors reduce significantly, giving excellent agreement with experimental values. The DFT results are in excellent (fortuitous?) agreement with the experimental value for activation energy for 1,2-DCE while the MP2 and HF results seem to overestimate the barrier. However, DFT results for EC is 4.5 kcal mol~(-1) less than the previously reported experimental values. At all levels, theory predicts an increase in HCl elimination barrier on β-Cl substitution on EC.
机译：已经研究了在单脉冲激波管中反射激波后的1050至1175 K的温度范围内1,2-二氯乙烷（1,2-DCE）的热分解。发现在这些条件下，单分子消除HCl是1,2-DCE分解的主要途径。从1,2-二氯乙烷中单分子去除HCl的速率常数为10〜（13.98±0.80）exp（-57.8±2.0 / RT）s〜（-1），其中活化能以kcal给出mol〜（-1），非常接近CH_3CH_2Cl（EC）的值。已经进行了从头算（HF和MP2）和DFT计算，以从EC和1,2-DCE查找该反应通道的活化势垒和过渡态的结构。在各种理论水平（HF / 6-311 ++ G **，MP2 / 6-311 ++ G **和B3LYP / 6-311 ++ G **）下计算的指数前因子为（≈10〜（ 15）s〜（-1））明显大于实验结果。如果将基态的扭转模式视为自由内旋，则指数前因子会显着降低，这与实验值非常吻合。 DFT结果与1,2-DCE的活化能实验值极佳（幸运地）一致，而MP2和HF结果似乎高估了这一障碍。然而，EC的DFT结果比以前报道的实验值小4.5 kcal mol〜（-1）。在所有水平上，理论都预测HCl消除EC上的β-Cl取代的障碍会增加。

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