环烯酸结合和基离子:什么时候开始分崩离析?
J M Tanko1, Xiangzhong Li, M'hamed Chahma
1Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA. jtanko@vt.edu
Journal of the American Chemical Society
|March 21, 2007
概括
循环衍生物的电化学还原揭示了不同的环开放率. 一些化合物经历了快速的环开放,而另一些由于共振稳定而表现出较慢的速度,其中一种显示出独特的重新排列机制.
科学领域:
- 电化学 电化学 电化学
- 有机化学 有机化学
- 反应机制 反应机制
背景情况:
- 环烯衍生物以其紧张环系统而闻名.
- 电化学还原为研究这些应力系统的反应性提供了一条途径.
- 了解替代剂对循环烯环开放的影响至关重要.
研究的目的:
- 为了研究各种1,2-diacylcyclopropane衍生物的电化学还原.
- 为了确定电子转移后环开放的动力学和机制.
- 探索替代剂对基离子稳定性和反应性的作用.
主要方法:
- 1,2-二亚乙基cyclopropane,1-乙基-2-phenylcyclopropane,1-乙基-2-基cyclopropane,和1,2-二基cyclopropane的电化学还原.
- 激素离子环开放的动态分析.
- 包括分子轨道计算在内的计算研究.
主要成果:
- 1-乙-2-烯基cyclopropane基离子有一个非常小的障碍环开放 (>10^7 s^-1).
- 由于共振稳定,基替代环 (7和8) 的环开放速度较慢 (10^5-10^6 s^-1).
- 1,2-二环 (8) 经历了一个意想不到的维尼环到环的重组,通过激素离子链机制.
- 1,2-二甲基cyclopropane (5) 的电化学还原结果是模两可的,表明要么简单的电子转移或协同解离电子转移 (DET).
结论:
- 替代组显著影响环衍生物的电化学还原路径和环开动力学.
- 代基团的共振稳定降低了环开放的速度.
- 对1,2-dibenzoylcyclopropane观察到一种新的乙烯基cyclopropane重排机制.
- 对于1,2-二甲cyclopropane的还原机制仍在争论中,可能涉及协同解离性电子转移.
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