在团中,甲基是捐电子还是取电子? 对o-carborane进行甲基化
Francesc Teixidor1, Gemma Barberà, Albert Vaca
1Institut de Ciència de Materials de Barcelona (CSIC), Campus U.A.B., E-08193 Bellaterra, Spain.
Journal of the American Chemical Society
|July 21, 2005
概括
团上的甲基组作为取电子的组,与常见的假设相反. 这种电子效应会影响反应性,正如核爱分子对甲基化团的攻击所证明的那样.
科学领域:
- 无机化学 无机化学
- 计算化学计算化学
- 有机化学 有机化学
背景情况:
- 甲基 (-Me) 通常被认为是附着在碳原子上的电子捐赠体.
- 团中的替代物的电子行为可能与碳系统中的行为有很大差异.
- 了解替代物效应对于预测和控制集群的反应性至关重要.
研究的目的:
- 为了研究集中的原子附着的甲基组的电子性质.
- 确定甲基化对团电子性质和反应性的影响.
- 提供理论和实验证据,证明上甲基的电子吸收性质.
主要方法:
- 使用B3LYP/6-31G*理论水平进行密度函数理论 (DFT) 计算.
- 穆利肯电荷分析以量化原子的电荷分布.
- 经过试验合成的甲基化集群.
- 在合成的集群上进行核替代反应.
主要成果:
- 理论计算表明,甲基组替代会使的穆利肯电荷增加 +0.18 个单位,这表明有电子吸收效应.
- 甲基化导致团上显著的正电荷积累,这影响了它的反应性.
- 实验合成证实了甲基化集群的形成,随后的反应表明在特定位置对核友性攻击的敏感性.
结论:
- 在团中的原子附着的甲基组作为电子吸收组起作用,挑战了它们电子捐赠性质的一般假设.
- 甲基组的电子吸收效应导致缺电子的中心,使得集群容易受到核友的攻击.
- 这一发现对各种化学领域的功能化集群的合成和应用有影响.
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