The reaction of Br atoms with toluene was investigated by employing various quantum chemical methods and statistical rate theory calculations. Various composite methods such as CBS‐QB3, G3, and G4 were used to obtain the energy profiles of the Br + toluene reaction. Further single‐point calculations of the stationary points were performed at the CCSD(T)/cc‐pV(D,T)Z level of theory using B3LYP/cc‐pVTZ and MP2/aug‐cc‐pVDZ optimized geometries. Our calculations revealed several reaction pathways in the potential energy surface of the Br + toluene reaction. However, the reaction pathway that abstracts hydrogen atoms from the methyl site of toluene was found to be energetically the most favorable. This reaction pathway appears to proceed via a complex forming mechanism, similar to that seen in the reactions of cyclic ethers with Br atoms. Our calculations reveal that the reaction of a Br atom with toluene proceeds exclusively via intermediate complexes in an overall endothermic addition‐elimination mechanism. Based on the ab initio results, the standard enthalpies of formation of the product radicals and the rate coefficients for the relevant reaction pathways are computed. The calculated values of the enthalpy of formation are found to match excellently with the available literature data. Lowering the barrier height of hydrogen abstraction reaction at the methyl site by less than 4 kJ/mol, the calculated rate coefficients, k_ov(T) = 1.36 × 10^–23 T^3.687 exp(−4.57 K/T) cm³ molecule^–1 s^–1, reproduced the experimental data excellently from 200 to 500 K.

中文翻译：

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原子溴与甲苯反应的理论动力学研究

通过采用多种量子化学方法和统计速率理论计算，研究了Br原子与甲苯的反应。使用各种复合方法（例如CBS-QB3，G3和G4）获得Br +甲苯反应的能谱。使用B3LYP / cc-pVTZ和MP2 / aug-cc-pVDZ优化的几何结构，在理论上的CCSD（T）/ cc-pV（D，T）Z级别上对定点进行了进一步的单点计算。我们的计算揭示了Br +甲苯反应的势能面中的几种反应途径。然而，发现从能量上从甲苯的甲基位置提取氢原子的反应途径在能量上是最有利的。该反应途径似乎是通过复杂的形成机理进行的，类似于在环醚与Br原子反应中看到的过程。我们的计算表明，在整个吸热加成-消除机理中，Br原子与甲苯的反应仅通过中间配合物进行。根据从头算的结果，计算产物自由基形成的标准焓和相关反应途径的速率系数。发现形成焓的计算值与可获得的文献数据非常匹配。将甲基位置的氢提取反应的势垒高度降低不到4 kJ / mol，计算得出的速率系数为 计算产物自由基形成的标准焓和相关反应途径的速率系数。发现形成焓的计算值与可获得的文献数据非常匹配。将甲基位置的氢提取反应的势垒高度降低不到4 kJ / mol，计算得出的速率系数为 计算产物自由基形成的标准焓和相关反应途径的速率系数。发现形成焓的计算值与可获得的文献数据非常匹配。将甲基位置的氢提取反应的势垒高度降低不到4 kJ / mol，计算得出的速率系数为k _ov（T）= 1.36×10 ^–23 T ^3.687 exp（-4.57 K / T）cm ³分子^–1 s ^–1，很好地再现了200至500 K的实验数据。