气相中n,pi*激发状态的火:绝对反应性和选择性的变化
Dieter Klapstein1, Uwe Pischel, Werner M Nau
1Department of Chemistry, St. Francis Xavier University, Antigonish, Nova Scotia B2G 2W5, Canada.
Journal of the American Chemical Society
|September 19, 2002
概括
电子捐赠者对激发性阿佐的气相火揭示了涉及和直接转移的机制. 溶解显著影响反应性,特别是对极性O-H和N-H键.
科学领域:
- 摄影化学的使用.
- 化学动力学 化学动力学
- 有机化学 有机化学
背景情况:
- 亚索呈现出 n,pi* 激发状态,容易被电子和捐赠者灭.
- 了解气相中火机制对于解释溶剂在溶液中的作用至关重要.
研究的目的:
- 通过各种含有异原子的捐赠体,研究激发性阿佐的气相火机制.
- 阐明外接线形成与直接转移之间的作用.
- 为了比较气相反应性与溶液相观测,特别是反转溶剂效应.
主要方法:
- 使用2,3-diazabicyclo[2.2.2]oct-2-ene和19种不同的捐赠物 (胺基,硫化物,,醇) 的气相火实验.
- 测量9种化衍生物的同位素效应.
- 反应速率的动态分析和气相和溶液相之间的比较.
主要成果:
- 有证据表明与三级胺和硫化物激发的电荷转移复合体 (exciplexes).
- 从C-H,N-H和O-H债券中确定有竞争力的直接转移.
- 气相速常数比溶液中大得多,支持反向溶剂效应.
- 极性O-H和N-H键在溶解时表现出较大的反应性下降,而极性较小的C-H键则表现出较大的反应性下降.
结论:
- 这项研究支持某些捐赠者参与exciplex,而另一些捐赠者则直接转移气,用于气相酸 quenching.
- 气相动力学提供了关于在溶液中观察到的"反向溶剂效应"的见解.
- 在光诱导的抽象中,溶解对极性与非极性键的反应性有不同的影响.
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