在乙烯基碳中,核友替代的配置逆转与保留
R D Bach1, A G Baboul, H B Schlegel
1Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, USA.
Journal of the American Chemical Society
|June 14, 2001
概括
计算研究揭示了气相核友乙烯基替代机制. 未激活的乙烯基化物倾向于西格玛攻击,而激活的二乙烯则倾向于PI途径,尽管两者都有高能量屏障.
科学领域:
- 计算化学的计算化学
- 有机反应机制 有机反应机制
背景情况:
- 核性乙烯基替代 (Nu-V) 在有机合成中至关重要.
- 了解气相机制为反应性提供了基本的见解.
- 以前的研究表明,Nu-V反应的复杂途径.
研究的目的:
- 通过计算来研究核性乙烯基替代的气相机制.
- 为了确定不同乙烯基基板的首选攻击途径 (sigma vs. pi).
- 分析基质激活和复杂化对反应通路的影响.
主要方法:
- 使用了包括Coupled Cluster Singles Doubles (CCSD),CCSD ((T) 和G2 ((+) 在内的高级计算方法.
- 使用CCSD/6-31+G*和CCSD(T)/6-31+G*进行了几何优化.
- 理论计算探讨了离子 (Cl-) 与乙烯基化物和1--1-乙烯的反应.
主要成果:
- 未激活的乙烯基化物通过单阶段的西格玛攻击经历气相Nu-V.
- 适度激活的1--1-乙烯有利于单步PI攻击途径.
- 与Na(+) 复合并没有改变对化乙烯的西格玛偏好.
- 气相反应的计算激活障碍是过高的.
结论:
- 气相Nu-V反应表现出不同的sigma和pi路径,这取决于基质的激活.
- 高能障碍表明,溶解和 counterions 对于凝聚相反应至关重要.
- 在溶液中,电子吸收组可能通过碳联中间体促进Nu-V.
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