机械洞察力和溶剂效应对不稳定的SCN- + CH3Cl反应在水溶液:一个多层次的QM/MM研究
Nan Wang1, Yilin Cheng1, Chen Li1
1College of Physics and Electronics, Shandong Normal University, Jinan, Shandong 250014, China.
The journal of physical chemistry. A
|November 20, 2025
概括
酸离子 (SCN) 与水中的甲基化物 (CH3Cl) 的 SN2 反应倾向于S侧攻击. 溶剂效应增加了激活障碍,但保持了这种偏好,为溶液相反应机制提供了关键的见解.
科学领域:
- 计算化学计算化学
- 物理化学 物理化学
- 化学动力学 化学动力学
背景情况:
- SCN-+CH3Cl的双向SN2反应可以通过S侧或N侧攻击进行,气相机制之前已经研究过.
- 这种反应的机理细节和水溶液中的溶剂作用尚不清楚.
研究的目的:
- 为了研究SCN- + CH3Cl反应在水溶液中的原子水平的两难机制.
- 阐明溶剂对反应路径和能量学的作用.
主要方法:
- 使用了多层次的量子力学/分子力学 (QM/MM) 方法.
- 采用显式水模型来模拟反应环境.
- 使用CCSD (T) 理论水平计算平均力 (PMF) 的潜力.
主要成果:
- 在S侧和N侧攻击路径之间观察到不同的结构和电荷转移动态.
- 与N侧过渡状态相比,S侧过渡状态更类似于反应物复合体.
- 自由能量障碍被计算为S侧攻击的21.4 kcal/mol和N侧攻击的26.3 kcal/mol,表明S侧在溶液中的偏好.
- 与气相值相比,溶剂效应使激活障碍增加了约31% (S侧) 和约34% (N侧).
结论:
- 在水溶液中,S侧攻击路径是SCN-+CH3的SN2反应的优先选择.
- 溶剂效应显著调节反应能量,提高激活障碍,但保持内在的S侧偏好.
- 这项研究提供了原子层面的洞察力,了解两位反应的反应性以及溶剂在SN2反应中的关键作用.
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