在盐中退化的核替代
Elizabeth V Jennings1, Kirill Nikitin, Yannick Ortin
1Centre for Synthesis and Chemical Biology, School of Chemistry and Chemical Biology, University College Dublin , Dublin 4, Ireland.
Journal of the American Chemical Society
|November 12, 2014
概括
在酸上发生退化化物替代通过两步机制,涉及五坐标中间体. 实验和计算研究揭示了影响这种重要的化学反应的能量障碍和硬质效应.
科学领域:
- 有机化学化学 有机化学
- 反应机制 反应机制
- 计算化学的计算化学
背景情况:
- 在四坐标酸酸上发生的退化化物替代反应是有机化学的基础.
- 了解机制和能量障碍对于预测反应性和设计新的合成路径至关重要.
研究的目的:
- 阐明在酸酸上变性化物替代的机制并确定能量障碍.
- 研究替代剂对反应速率和立体化学的影响.
- 将实验结果与计算预测进行比较,以获得机械洞察力.
主要方法:
- 使用了可变温度 (VT) 和交换光谱 (EXSY) 核磁共振 (NMR) 技术.
- 一个新的实验设计,利用一种性替代物 ((s) Bu) 来解决退化的盐.
- 开发了计算化学方法来建模反应系统并分析能量配置文件.
主要成果:
- 一个涉及背部攻击和解离形成五坐标二酸中间体的两步机制得到了强烈支持.
- 经过实验确定的能量障碍范围从<9到近20千卡的mol(-1),不包括贝里伪旋转.
- 化的能量障碍低于类相对应物,这是由于五坐标中间体的更容易获得.
- 大量的替代剂 (Me < Et < (i) Pr < (t) Bu) 减缓了反应,与关联机制和硬质障碍相一致.
- 观察到第一阶动力学,归因于溶液中存在离子对.
- 更多的O'Ferrall-Jencks图表显示了三角形二金字塔中间体的浅潜在井.
结论:
- 这项研究证实了在酸酸上发生退化的化物替代的两步关联机制.
- 能量障碍受到化物标识和替代物的硬质体积的影响.
- 计算和实验数据提供了对反应路径和中间结构的全面了解.
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