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什么时候中间体变成过渡状态? 在 (S) - 1 - 3 - - 尼托菲尼尔) 乙基酸盐溶解过程中,在没有竞争性种族化的情况下发生退化异构化
1Department of Biochemistry and Applied Chemistry, Kurume National College of Technology, Komorinomachi, Kurume 830-8555, Japan.
Journal of the American Chemical Society
|December 21, 2006
概括
在溶解过程中监测了 (S) - 1 - 3 - - 尼托芬乙基酸盐的基质纯度. 异构化通过避免常见的离子对中间体的途径发生,这表明溶解的逐步预关联机制.
科学领域:
- 有机化学 有机化学
- 反应机制 反应机制
- 立体化学是一种立体化学.
背景情况:
- 研究溶解反应的立体化学结果对于理解反应机制至关重要.
- 在溶解条件下的性托西拉酸盐的行为为电离和中间形成提供了洞察力.
研究的目的:
- 为了确定在溶解过程中 (S) - 1 - 3 - - 尼托菲尼尔) 乙基酸盐的性纯度变化.
- 在这个系统中阐明异构化和种族化的机制.
- 用理论预测来比较种族化和异构化速率.
主要方法:
- 合成 (S) - 1 - 3 - - 尼托菲尼尔) 乙基托西酸盐,具有较高的反体过量 (> 99%).
- 在50:50三乙醇/水混合物中的溶解过程中监测奇拉纯度变化.
- 动力分析以确定种族化 (k(rac)) 和异构化 (k(iso)) 的速率常数.
主要成果:
- 在两个半衰期后观察到最小的种族化 (0.5% (R) -2-OTs).
- 计算的种族化速率常数 (k(rac) ≈ 4 x 10^-6 s^-1) 显著小于异构化速率常数 (k(iso) = 3.2 x 10^-4 s^-1).
- 观察到的k(rac) 也小于涉及常见离子对中间体的机制预测值.
结论:
- 异构反应主要通过绕过常见离子对中间体的形成的途径进行.
- 2-OTs的溶解可能通过一个阶段性预关联机制发生,这涉及在基质离子化之前的溶剂重组.
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