Theoretical Investigation into Rate-Determining Factors in Electrophilic Aromatic Halogenation
Theoretical Investigation into Rate-Determining Factors in Electrophilic Aromatic Halogenation
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DOI：
10.1021/acs.jpca.7b10781
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发表时间：
2018-03-29
影响因子：
2.9
通讯作者：
Brinck, Tore
中科院分区：
文献类型：
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作者：
Liljenberg, Magnus;Stenlid, Joakim Halldin;Brinck, Tore
采用密度泛函理论在PCM-M06-2X/6-311G（d,p）水平上研究了单取代苯在水溶液中的卤化反应。与Cl-2的反应首先形成C原子配位的pi配合物，然后形成速率决定的sigma配合物。最后一部分是通过水分子或弱碱将质子抽离而进行的。我们评估了西格玛配合物作为速率决定过渡态（TS）模型的使用，并发现该模型越晚出现在反应坐标上，TS越准确。这解释了与硝化（早期TS）相比，卤化（晚期TS）模型的准确性更高；也就是说，底物越失活，TS越晚。Br-2的卤化反应与相应的氯化反应的机理相似，但溴化反应有一个非常晚的速率决定TS，其能量与sigma配合物相似。ICl的碘化作用机理与氯化和溴化作用机理不同。在-配合物形成后，反应以协调的方式进行，没有-配合物。该反应具有较大的原生氢动力学同位素效应，与实验结果一致。
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 pi-complex and is followed by the formation of the sigma-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 sigma-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 sigma-complex in energy. The iodination with ICl follows a different mechanism than chlorination and bromination. After the formation of the pi-complex, the reaction proceeds in a concerted manner without a sigma-complex. This reaction has a large primary hydrogen kinetic isotope effect in agreement with experimental observations.