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在化学反应中遵循分子运动:没有积极推进的证据
Lucy L Fillbrook1, Jan-Philipp Günther2,3, Günter Majer2
1School of Chemistry, UNSW Sydney, Sydney, NSW 2052, Australia.
Journal of the American Chemical Society
|December 2, 2021
概括
磁性离子可以干扰反应期间的扩散测量. 使用混合梯度或放松剂的新方法使精确的扩散NMR能够反驳"增强移动性"的说法并揭示反应机制.
科学领域:
- 化学运动学
- 物理化学
- 核磁共振 (NMR) 光谱学
背景情况:
- 在此之前的研究中,研究人员认为,在对酸的反应中,分子扩散发生了变化.
- 增强移动性
- 这种现象通常使用核磁共振 (NMR) 扩散技术进行测量.
- 然而,在反应过程中变化的磁性离子度可能会影响NMR信号强度,导致不准确的扩散测量.
研究的目的:
- 证明对磁性离子对扩散NMR测量的影响.
- 开发和验证在反应过程中精确的扩散测量方法.
- 调查铜催化酸循环添加反应中的扩散行为,并重新评估
- 增强移动性
- 没有.
主要方法:
- 在扩散核磁共振中利用混合梯度幅度来弥补由磁性离子引起的时间依赖放松率.
- 采用了一种偏磁放松剂,同时确定扩散系数和反应动力学.
- 应用补充性NMR技术和密度函数理论 (DFT) 计算以获得机械洞察力.
- 使用替代性减少剂来解决NMR信号重叠问题.
主要成果:
- 即使在偏磁离子度波动的情况下,也可以实现精确的扩散NMR测量.
- 在铜催化酸循环添加反应中没有观察到全球扩散系数的增加.
- 由于与铜催化剂结合,基反应物的扩散速度减慢,这表明中间形成.
- NMR和DFT计算证实了这种催化中间体的形成.
结论:
- 显然是因为
- 增强移动性
- 在NMR测量过程中是对磁离子干扰的产物.
- 随着适当的方法修正,时间解析的扩散核磁共振 (NMR) 提供了对反应机制的准确见解.
- 这项研究挑战了在化学反应过程中分子自我推进的先前解释.
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