在气相S(N) 2和E2反应中的动态同位素效应:实验与理论的比较
Stephanie M Villano1, Shuji Kato, Veronica M Bierbaum
1University of Colorado, Department of Chemistry and Biochemistry, 215 UCB, Boulder, Colorado 80309-0215, USA.
Journal of the American Chemical Society
|January 19, 2006
概括
这项研究研究了化与化离子的气相反应,揭示了随着基组替代增加,消除反应成为主导的. 乙基化物的实验结果偏离了计算预测.
科学领域:
- 化学动力学 化学动力学
- 反应机制的反应机制
- 气相化学 气相化学
背景情况:
- 了解像双分子核替代 (SN2) 和基因诱导消除 (E2) 这样的竞争反应途径在化学动力学中至关重要.
- 动态同位素效应 (KIE) 是阐明反应机制和过渡状态结构的强大工具.
研究的目的:
- 调查SN2和E2反应途径之间的竞争,用于RCl + ClO- (R = 甲基,乙基,异基,三基) 的气相反应.
- 测量这些反应的KIE和整体速率常数,使用流动后光选择离子流管 (FA-SIFT) 仪器.
- 将实验结果与C2H5Cl + ClO-.反应的计算预测进行比较.
主要方法:
- 使用FA-SIFT仪器对气相离子分子反应进行精确的动力测量.
- 使用动态同位素效应 (KIE) 测量来区分反应机制.
- 执行计算化学计算以与实验数据进行比较.
主要成果:
- 实验结果表明,随着基化物 (RCl) 的替代程度的增加,对E2消除道的转移.
- KIEs的系统变化表明,C2H5Cl + ClO-反应的SN2和E2路径同时发生,与理论预测保持一致.
- 在实验反应速率常数和KIE以及相应的计算结果之间观察到显著的偏差.
结论:
- 基替代的程度强烈影响主导反应路径,有利于消除 (E2) 代替 (SN2) 增加替代.
- 虽然计算模型预测了SN2和E2路径的共存,但实验数据显示了反应速率和KIE的差异,突出了这个系统当前理论模型的局限性.
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