离子在水性介质中的稳定性和分离
D A Lawlor1, R A More O'Ferrall, S N Rao
1Department of Chemistry and Centre for Synthesis and Chemical Biology, University College Dublin, Belfield, Dublin 4, Ireland.
这项研究量化了在溶解反应中甲离子中间体的反应性. 它揭示了质子转移的反应性低于水的核友性攻击,影响烯水化机制.
科学领域:
- 物理有机化学 有机化学
- 反应动力学反应动力学
- 碳化物化学 碳化物化学
背景情况:
- 溶解反应通常通过像碳酸这样的反应性中间体进行.
- 了解这些中间体的竞争反应途径对于阐明反应机制至关重要.
- 芳香系统可以形成稳定的离子,影响它们的反应性.
研究的目的:
- 为了研究 fenathrenonium 离子中间体的竞争反应.
- 为了确定速度和平衡常数,其与水和作为一个基础的反应.
- 为了将碳酸稳定性与反应途径相关联,并与其他芳香系统进行比较.
主要方法:
- 在水性酸中溶解9-dichloroacetoxy-9,10-dihydrophenanthrene. 在水性酸中溶解.
- 使用亚离子作为陷和"时钟"测量产品比率.
- 动力分析以确定速率常数 (kp,kH2O) 和平衡常数 (pKa,pKR).
主要成果:
- 测量了烯离子的速率常数: kp = 3.7 x 10^10 s^-1 和 kH2O = 1.5 x 10^8 s^-1.
- 确定了平衡常量pKa = -20.9和pKR = -11.6的情况.
- 对和1-甲离子的额外推算值表明其稳定性很高.
结论:
- 对于这些carbocations来说,质子转移本质上比水的核友攻击更不具反应性.
- 发现分区比和水化平衡常数之间存在相关性.
- 这种反应性模式解释了烯水化中的速度决定性步骤,特别是在稳定芳香系统中.
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