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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Theoretical Investigation into Rate-Determining Factors in Electrophilic Aromatic Halogenation
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Theoretical Investigation into Rate-Determining Factors in Electrophilic Aromatic Halogenation

机译：电泳芳族卤化中速率测定因子的理论研究

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摘要

The halogenation of monosubstituted benzenes in aqueous solvent was studied using density functional theory at the PCM-M06-2X /6-311G(d,p) level. The reaction with Cl_(2) begins with the formation of C atom coordinated π-complex and is followed by the formation of the σ-complex, which is rate-determining. The final part proceeds via the abstraction of the proton by a water molecule or a weak base. We evaluated the use of the σ-complex as a model for the rate-determining transition state (TS) and found that this model is more accurate the later the TS comes along the reaction coordinate. This explains the higher accuracy of the model for halogenations (late TS) compared to nitrations (early TS); that is, the more deactivated the substrate the later the TS. The halogenation with Br_(2) proceeds with a similar mechanism as the corresponding chlorination, but the bromination has a very late rate-determining TS that is similar to the σ-complex in energy. The iodination with ICl follows a different mechanism than chlorination and bromination. After the formation of the π-complex, the reaction proceeds in a concerted manner without a σ-complex. This reaction has a large primary hydrogen kinetic isotope effect in agreement with experimental observations.
机译：使用密度官能理论在PCM-M06-2 X / 6-311g（D，P）水平上使用密度官能理论研究了含水溶剂中的单溶质苯的卤化。与Cl_（2）的反应开始于C原子的形成配位π-复合物，然后形成σ-复合物，其是速率测定的。最后一部分通过水分子或弱碱通过质子的抽象进行。我们评估了使用Σ复合物作为速率确定过渡状态（TS）的模型，发现该模型更准确，后者Ts沿着反应坐标。这解释了与硝化（早期TS）相比卤化模型（TS）模型的更高准确性;也就是说，稍后的TS越钝。用BR_（2）的卤化与相应的氯化相似的机制进行，但溴化具有非常晚的速率确定TS，其类似于能量中的σ复合物。用ICL碘化伴随不同的机制而不是氯化和溴化。在形成π复合物之后，反应以齐心的方式进行，没有σ复合物。该反应具有大的氢动力学同位素效应与实验观察。

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