氧化物是同芳香的吗? 一个微热度测量研究
Z S Jia1, P Brandt, A Thibblin
1Contribution from the Institute of Chemistry, University of Uppsala, Box 531, S-751 21 Uppsala, Sweden.
Journal of the American Chemical Society
|October 18, 2001
概括
氧化物由于同体芳香化而表现出不寻常的稳定性,这解释了它在酸催化反应中的低反应性. 这种热力学稳定性是理解其化学行为的关键.
科学领域:
- 物理有机化学 有机化学
- 计算化学是一种计算化学.
- 反应动力学反应动力学
背景情况:
- 芳香化反应是有机化学的基础.
- 氧化和酸是理解芳香度的关键中间体.
- 以前的研究表明,在氧化中具有同芳香的稳定性.
研究的目的:
- 测量氧化和酸芳香化反应的反应和速率常数.
- 为了比较这些化合物的热力学稳定性和反应性.
- 阐明导致氧化物的异常稳定性和低反应率的因素.
主要方法:
- 热流微热量计用于测量反应度.
- 采用了B3LYP混合功能计算与AM1/SM2溶解校正.
- 与相关的循环二烯氧化物和循环二醇反应进行比较.
主要成果:
- 氧化的反应热量 (ΔH = -57.0 kcal mol−1) 显著大于酸的反应热量 (ΔH = -38.7 kcal mol−1).
- 与其热力学驱动力相比,氧化物表现出异常低的反应性 (速率比率为0.08).
- 计算和测量的热量对齐,支持在氧化中 homoaromatic 稳定.
结论:
- 氧化物通过同体芳香化显著稳定,从而使其反应性降低.
- 这种不寻常的稳定性解释了观察到的107倍低于预期的反应率的一半以上.
- 其余的反应性下降归因于高能碳酸形成的过渡状态.
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