芳鎓离子的超芳香稳定化。

Hyperaromatic stabilization of arenium ions.

机构信息

School of Chemistry and Chemical Biology, University College Dublin, Belfield, Dublin 4, Ireland.

出版信息

Org Lett. 2010 Dec 3;12(23):5550-3. doi: 10.1021/ol1014027. Epub 2010 Nov 5.

Abstract

Benzene-cis- and trans-1,2-dihydrodiols undergo acid-catalyzed dehydration at remarkably different rates: k(cis)/k(trans) = 4500. This is explained by formation of a β-hydroxycarbocation intermediate in different initial conformations, one of which is stabilized by hyperconjugation amplified by an aromatic no-bond resonance structure (HOC(6)H(6)(+) ↔ HOC(6)H(5) H(+)). MP2 calculations and an unfavorable effect of benzoannelation on benzenium ion stability, implied by pK(R) measurements of -2.3, -8.0, and -11.9 for benzenium, 1-naphthalenium, and 9-phenanthrenium ions, respectively, support the explanation.

摘要

苯顺式-和反式-1,2-二氢二醇在酸催化下脱水的速率差异显著：k(cis)/k(trans) = 4500。这可以通过β-羟基碳正离子中间体在不同初始构象中的形成来解释，其中一种构象通过芳香无键共振结构（HOC(6)H(6)(+) ↔ HOC(6)H(5) H(+))得到超共轭稳定。MP2 计算和 pK(R)测量对苯鎓离子稳定性的不利影响，分别为苯鎓、1-萘鎓和 9-菲鎓离子的 -2.3、-8.0 和 -11.9，支持了这一解释。