对硫转移反应的同位素效应和介质效应
R H Hoff1, P Larsen, A C Hengge
1Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322-0300, USA.
Journal of the American Chemical Society
|September 20, 2001
概括
硫转移反应的p-尼托芬硫酸盐 (pNPS) 显示类似的过渡状态转移反应,但在他们的响应溶剂变化显著不同. 中等效应大大加快了酸转移,而仅适度影响了硫转移.
科学领域:
- 生物化学 生物化学
- 化学动力学 化学动力学
- 有机化学 有机化学
背景情况:
- 硫转移反应在机理上与转移反应相似.
- 了解这些反应机制对于各种生化过程至关重要.
研究的目的:
- 研究p-nitrophenyl硫酸盐 (pNPS) 在硫转移反应中的动态同位素效应和介质效应.
- 将这些发现与以前关于基转移反应的研究进行比较.
主要方法:
- 对N-15和O-18动态同位素效应的测量.
- 使用不同的溶剂组成 (例如,DMSO) 和核友素 (例如,三氨基醇) 分析介质效应.
- 反应速率和过渡状态特征的比较.
主要成果:
- 对于pNPS离子的N-15和桥梁O-18同位素效应与p-尼托酸 (pNPP) 离子相似,表明在过渡状态下存在显著的键裂解.
- 非桥梁O-18同位素效应表明,硫基在过渡状态下类似于SO3 .
- 与酸转移反应相比,硫转移反应表现出明显不同的介质效应,在近溶剂和酒精核中速度加速要小得多.
结论:
- 硫和转移的过渡状态共享机理上的相似性,与离开组的实质性债券分离.
- 在中性pNPS在酸中的反应的过渡状态中,质子转移在很大程度上已经完成,类似于pNPP monoanion.
- 对介质效应的独特反应突出显示了硫和转移反应之间的溶解和过渡状态稳定性的根本差异.
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