从质子合电子转移 (PCET) 的角度来看,原子转移反应中的极性效应:来自托卢的抽象
Benjamin D Groff1, Brian Koronkiewicz1, James M Mayer1
1Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States.
The Journal of organic chemistry
|November 18, 2023
概括
通过检查质子和电子转移中的自由能量变化,可以更好地理解原子转移反应. 极地效应显著影响反应障碍,偏离传统模型.
科学领域:
- 物理有机化学 有机化学
- 化学动力学 化学动力学
- 反应机制分析 反应机制分析
背景情况:
- 原子转移 (HAT) 反应是化学的基础.
- 了解影响HAT反应速率的因素对于预测反应性至关重要.
- 以前的研究往往侧重于变化,不太重视自由能量相关性.
研究的目的:
- 为了重新分析替代多烯的HAT反应的速率常数.
- 研究HAT激活能量与质子转移 (PT) 和电子转移 (ET) 的自由能量之间的关系.
- 探索极效应对HAT反应障碍物的影响.
主要方法:
- 使用编制或估计的pKa和E°值来计算PT和ET反应的自由能量.
- 应用Eyring过渡状态理论来分析激活能量 (ΔGHAT‡).
- 将 ΔGHAT‡ 与热力学参数相关联 (ΔG°HAT, ΔG°PT, ΔG°ET).
主要成果:
- 耳环激活能量 (ΔGHAT‡) 与 ΔG°PT 和 ΔG°ET 线性相关,但与 ΔG°HAT 不相关.
- 观察到一种"极性效应",导致与氧基相比,三丁基的屏障发生相反的转移.
- 贝尔-埃文斯-波兰尼 (BEP) 效应仅占 ΔG°HAT. 的变化的 5-10%.
- 突出了极性效应和异步HAT反应之间的联系.
结论:
- 自由能量分析提供了对HAT反应障碍的更准确的理解,而不是单纯的热量.
- 极地效应在调节HAT反应选择性方面发挥着重要作用.
- 这些发现表明,在HAT反应中预测选择性的潜在框架,包括反热力学结果.
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