Abstract

DFT calculations at the LC-wHPBE/6-311++G(d,p) level found that the solvolysis of t-butyl chloride or bromide in water or alcohol has two paths: a frontside path and a backside path. The frontside path is a three-step reaction. The first step is to remove a halogen anion and generate the carbocation (CH₃)₃C⁺, and it follows the Lewis collision theory and needs to overcome a barrier E_a. The carbocation is the first active intermediate in the solvolysis. The second step is that the carbocation and two solvent molecules (CH₃)₃C⁺ + 2R–OH (R = H or alkyl) to complete a spontaneous termolecular electrophilic addition A_E3, in which the carbocation is the electrophile, and the product is an σ-complex that it is the second active intermediate in solvolysis. The third step is the generation of the product through a spontaneous termolecular proton transfer T_p3 of the σ-complex. The backside path is a two-step reaction. The first step is a termolecular nucleophilic substitution S_N3 of (CH₃)₃C–Cl or –Br + 2R–OH, the substitution follows the transition state theory and has to overcome an activition barrier ∆E*. The product is the same σ complex as in the frontside path. The second step is the termolecular proton transfer T_p3 of the σ complex to generate the target product also. Thus the T_p3 is a shared step in the two paths. The two paths contain three termolecular reactions, and the last solvent molecule is a catalyst. Both paths are a four-molecular solvolysis processes involving one molecule of the alkyl halide and three solvent molecules, and are weakly or very weakly endothermic reactions. High-resolution ESI–MS confirmed the presence of the two paths and the two active intermediates. Based on the results, a solvent-catalyzed four-molecular two-path solvolysis mechanism of (CH₃)₃C–Cl or –Br in water or alcohol proposed.

中文翻译：

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密度泛函理论计算并通过高分辨率电喷雾电离质谱法确定的叔丁基氯或溴化物在水中或乙醇中的溶剂催化四分子两路径溶剂化机理

摘要

在LC-wHPBE / 6-311 ++ G（d，p）级别的DFT计算发现，叔丁基氯或溴化物在水或酒精中的溶剂分解有两条路径：前侧路径和后侧路径。前端路径是三步反应。第一步是除去卤素阴离子并生成碳正离子（CH ₃）₃ C ⁺，它遵循路易斯碰撞理论，需要克服势垒E _a。碳正离子是溶剂分解中的第一个活性中间体。第二步是碳正离子和两个溶剂分子（CH ₃）₃ C ⁺ + 2R–OH（R ​​= H或烷基）完成自发的分子亲电加成反应A _E在图3中，碳正离子是亲电子体，产物是σ-络合物，它是溶剂分解中的第二种活性中间体。第三步是通过σ络合物的自发分子间质子转移T _p 3生成产物。背面路径是两步反应。第一步是（CH ₃）₃ C–Cl或–Br + 2R–OH的分子亲核取代S _N 3 ，该取代遵循过渡态理论并且必须克服激活障碍∆ E *。乘积与前端路径中的σ复数相同。第二步是分子质子转移T _p3的σ复数也生成目标乘积。因此，Ť _p 3是在两个路径共享的步骤。这两个路径包含三个分子反应，最后一个溶剂分子是催化剂。两种途径都是涉及一个分子的卤代烷和三个溶剂分子的四分子溶剂分解过程，并且是弱或非常弱的吸热反应。高分辨率ESI-MS证实了两条路径和两种活性中间体的存在。根据这些结果，提出了在水或酒精中溶剂催化的（CH ₃）₃ C–Cl或–Br的四分子两路径溶剂分解机理。