Addition–Elimination versus Direct Substitution Mechanisms for Arene Chlorination
Addition–Elimination versus Direct Substitution Mechanisms for Arene Chlorination
复制标题
芳烃氯化的加成-消除机制与直接取代机制
DOI：
10.1002/ejoc.201402765
复制
发表时间：
2014
影响因子：
2.8
通讯作者：
P. Schleyer
中科院分区：
文献类型：
--
作者：
B. Galabov;G. Koleva;Jing Kong;H. Schaefer;P. Schleyer
在B3 LYP-D3/6-311+G（2d，2 p）水平上对芳烃（苯、甲苯和萘）在非极性溶剂（CCl 4）中的氯化反应进行了理论模拟，揭示了两种可供选择的反应途径，即直接取代和加成-消除，这两种途径都导致相同的取代产物.他们的障碍物的接近表明这些替代路线之间的竞争。这些机理途径都不包括σ-络合物中间体，这在传统上被认为是亲电芳族取代（SEAr）机理的关键特征。相反，直接取代途径涉及在反应物之间无势垒形成π-络合物之后的单个协同过渡态。HCl催化反应产物的催化效果的报告建模系统，大大降低了过渡态能量。计算出的反应势垒与实验建立的芳烃反应趋势非常雅阁。
Theoretical modelling of the chlorination of arenes (benzene, toluene and naphthalene) in a nonpolar solvent (CCl4) at the B3LYP-D3/6-311+G(2d,2p) level reveals two alternative reaction pathways, namely, direct substitution and addition–elimination, both of which lead to the same substitution products. The closeness of their barriers indicates competition between these alternative routes. Neither of these mechanistic pathways includes a σ-complex intermediate, which is traditionally believed to be a key feature of electrophilic aromatic substitution (SEAr) mechanisms. Instead, the direct substitution pathway involves a single concerted transition state following the barrierless formation of a π-complex between the reactants. The reported catalytic effect of HCl catalysis on the reaction product is modelled systematically and considerably decreases the transition-state energies. The computed reaction barriers are in excellent accord with the experimentally established reactivity trends for the arenes investigated.