Rate-Determining Factors in Nucleophilic Aromatic Substitution Reactions
Rate-Determining Factors in Nucleophilic Aromatic Substitution Reactions
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DOI：
10.1021/jo100195w
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发表时间：
2010-05-07
影响因子：
3.6
通讯作者：
Uggerud, Einar
中科院分区：
文献类型：
--
作者：
Fernandez, Israel;Frenking, Gernot;Uggerud, Einar
量子化学计算（OPBE/6-311++G（d，p））揭示了SNAr反应的电子因素。结果表明，用临界能表示的内禀亲核性（在同一取代反应X- + PhX X -> + X- + PhX中形成迈森海默结构Ph（X）（2）（-）所需的能量（Ph =苯基）显示以下近似趋势：NH 2-近似OH-近似F- >> PH 2-近似SH-近似Cl- > AsH 2-近似SeH-近似Br-。根据配价成键模型讨论了分子性质的周期趋势（表示亲核试剂的刘易斯碱性的X的质子亲和力和表示底物的刘易斯酸性的C（1 s）轨道能量）。利用能量分解法分析了反应的逐步进行过程和临界结构。增加的稳定性和由此增加的固有亲核性与Meisenheimer结构的芳族特征降低相关。这一明显的矛盾与使用同一模型的其他观察结果一致。
Quantum chemical calculations (OPBE/6-311++G(d,p)) have been performed to uncover the electronic factors that govern reactivity in the prototypical SNAr reaction. It was found that intrinsic nucleophilicity-expressed as the critical energy (the energy required for forming the Meisenheimer structure Ph(X)(2)(-)) in the identity substitution reaction X- + PhX X -> + X- + PhX (Ph = phenyl) shows the following approximate trend: NH2- approximate to OH- approximate to F- >> PH2- approximate to SH- approximate to Cl- > AsH2- approximate to SeH- approximate to Br-. The periodic trends are discussed in terms of molecular properties (proton affinity of X- expressing Lewis basicity of the nucleophile and C(1s) orbital energy expressing Lewis acidity of the substrate) based on a dative bonding model. Furthermore, the stepwise progress of the reactions and the critical structures are analyzed applying energy decomposition analysis. Increased stability, and thereby increased intrinsic nucleophilicity, correlates with decreasing aromatic character of the Meisenheimer structure. This apparent contradiction is explained in consistency with the other observations using the same model.