Molecular Mechanistic Study on the Electrophilic Substitution

亲电取代的分子机理研究

• 批准号: 03640413
• 负责人: OSAMURA Yoshihiro
• 金额: $ 1.28万
• 依托单位: RIKKYO UNIVERSITY (1992)Keio University (1991)
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for General Scientific Research (C)
• 财政年份: 1991
• 资助国家: 日本
• 起止时间: 1991 至 1992
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-03640413/
• 关键词: Electrophilic Substitution Reaction; Benzene-Chlorine complex; ab initio molecular orbital theory; Wheland complex; Potential Energy Surface; Chemical Reaction Pathway; 親電子置換反応; ベンゼン‐塩素錯体; ベンゼン・塩素錯体; 分子軌通計算

The electrophilic substitution reaction for aromatic hydrocarbon is one of most fundamental organic reactions. The reaction mechanism of aromatic electrophilic substitution reaction is thought to be via two stages. The first step is pi-type complex formation, and the second step is the proton elimination after the sigma-complex formation. This mechanism has been well accepted, but the detailed molecular processes have not been understood especially in conjunction with the solvent and Lowis acid catalyst. In this research, we have been studied the molecular mechanisms on the aromatic electrophilic substitution reactions theoretically in order to clarify the molecular structures of reaction complexes and theirpotential energy surfaces. Benzene and Cl_2 molecules are chosen as the first model. The pi-type complex of benzene-cl_2 is known to be charge-transfer complex, but this molecular interaction is very week and is concluded to be likely van der Waals interaction. Since the potential energy surfaces for the reaction from the pi-type complex indicate that the energy barriers are extremely high for both substitution pathway and addition reaction. This means that the active species to generate a chlorine cation must be considered, and we have examined the potential energy surface for the chlorination reaction of benzene with hydronium ion as a catalyst. When we include the hydronium ion to the benzene-Chlorine complex, two transition states have been found with very low energy barrier. These transition states correspond to the potential energy surface supported by the many experimental works. The first one is the formation of sigma-complex from pi-type complex. This sigma-complex must stabilize in order to proceed the elimination of proton via the second transition state.

芳烃的亲电取代反应是最基本的有机反应之一。芳香亲电取代反应的反应机理被认为是通过两个阶段。第一步是π型络合物的形成，第二步是σ络合物形成后的质子消除。这一机制已被广泛接受，但详细的分子过程还没有被理解，特别是与溶剂和Lowis酸催化剂。本论文从理论上研究了芳香亲电取代反应的分子机理，以阐明反应络合物的分子结构及其势能面。第一个模型选择苯和Cl_2分子。苯-氯的π型络合物是电荷转移络合物，但这种分子间相互作用很弱，可能是货车范德华相互作用。由于π型络合物反应的势能面表明，取代途径和加成反应的能垒都非常高。这意味着必须考虑产生氯阳离子的活性物种，并且我们已经研究了苯与水合氢离子作为催化剂的氯化反应的势能面。当我们将水合氢离子引入到苯-氯络合物中时，发现了两个能垒很低的过渡态。这些过渡态对应于许多实验工作所支持的势能面。第一种是π型络合物形成σ型络合物。这种σ-复合物必须稳定，以便通过第二过渡态进行质子消除。

项目成果

K.Nakamura & Y.Osamura: "Theoretical Study of the Reaction Mechanism and Migratory Aptitude of the Pinacol Rearrangement" Journal of American Chemical Society.

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