Unified mechanistic concept of electrophilic aromatic nitration: Convergence of computational results and experimental data
Unified mechanistic concept of electrophilic aromatic nitration: Convergence of computational results and experimental data
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DOI：
10.1021/ja021307w
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发表时间：
2003-04-23
影响因子：
15
通讯作者：
Olah, GA
中科院分区：
文献类型：
--
作者：
Esteves, PM;Carneiro, JWD;Olah, GA
对亲电芳香族硝化的机理进行了探讨。根据现有的实验数据和新的高阶量子化学计算，提出了一种涉及反应势能图上三个独立中间体的先前反应机理的修正。第一种，最初被认为是一种无取向的pi-配合物或电子供体-受体配合物（EDA），涉及氮离子和a-芳烃之间的高静电和电荷转移相互作用。它解释了在硝盐硝化过程中观察到的低底物选择性，同时保持了高的位置选择性，以及在气相中观察到的氧转移反应。随后的第二个中间体最初被认为是取向的“pi-配合物”，现在最好的代表是一个亲密的自由基阳离子-分子对，C6H6+/。NO2，即SET配合物，表明单电子从芳香a体系转移到NO2+。随后，它坍塌以提供最终的a-络合物中间体，即一个arenium离子。提出的亲电芳香族硝化的三个离散中间体统一了以前的机制建议，也有助于更好地理解这一根本重要的反应。先前得到的氧从NO2+转移到芳香环的ICR数据也符合所提出的机制。该反应势能表面上最稳定的中间体是苯酚和NO+之间的络合物。苯酚- no +络合物分解生成c6h60 +。/ phh +和NO，与ICR结果一致。
The mechanism of electrophilic aromatic nitration was revisited. Based on the available experimental data and new high-level quantum chemical calculations, a modification of the previous reaction mechanism is proposed involving three separate intermediates on the potential energy diagram of the reaction. The first, originally considered an unoriented pi-complex or electron donor acceptor complex (EDA), involves high electrostatic and charge-transfer interactions between the nitronium ion and the a-aromatics. It explains the observed low substrate selectivity in nitration with nitronium salts while maintaining high positional selectivity, as well as observed oxygen transfer reactions in the gas phase. The subsequent second intermediate originally considered an oriented "pi-complex" is now best represented by an intimate radical cation-molecule pair, C6H6+/.NO2, that is, a SET complex, indicative of single-electron transfer from the aromatic a-system to NO2+. Subsequently, it collapses to afford the final a-complex intermediate, that is, an arenium ion. The proposed three discrete intermediates in electrophilic aromatic nitration unify previous mechanistic proposals and also contribute to a better understanding of this fundamentally important reaction. The previously obtained ICR data of oxygen transfer from NO2+ to the aromatic ring are also accommodated by the proposed mechanism. The most stable intermediate of this reaction on its potential energy surface is a complex between phenol and NO+. The phenol-NO+ complex decomposes affording C6H6O+./PhOH+ and NO, in agreement with the ICR results.