Controlling the Conformational Energy of a Phenyl Group by Tuning the Strength of a Nonclassical CH···O Hydrogen Bond: The Case of 5-Phenyl-1,3-dioxane
作者:William F. Bailey、Kyle M. Lambert、Zachary D. Stempel、Kenneth B. Wiberg、Brandon Q. Mercado
DOI:10.1021/acs.joc.6b02428
日期:2016.12.16
with a ring oxygen of the dioxane. Acid-catalyzed equilibration of a series of anancomeric 2-tert-butyl-5-aryl-1,3-dioxane isomers demonstrates that remote substituents on the phenyl ring affect the conformational energy of a 5-aryl-1,3-dioxane: electron-withdrawing substituents decrease the conformational energy of the aryl group, while electron-donating substituents increase the conformational energy
Anancomeric 5-phenyl-1,3-dioxanes提供了一个独特的机会来研究控制构象的因子。人们可能期望1,3-二恶烷的C(5)处的轴向苯基具有与轴向苯基环己烷类似的构象,但一系列研究包括X射线晶体学,NOE测量和DFT计算表明,苯基为了使邻氢与二恶烷的环氧一起参与稳定的,非经典的CH··O氢键,优选将其放置在二恶烷环上。一系列ananomeromer 2- tert的酸催化平衡-丁基-5-芳基-1,3-二恶烷异构体表明,苯环上的远程取代基会影响5-芳基-1,3-二恶烷的构象能:吸电子取代基会降低芳基的构象能,给电子取代基增加了该基团的构象能。该效应与哈米特取代基参数非常线性相关。简而言之,可以响应于位于芳基环上的取代基的吸电子或供电子能力,以可预测的方式调节CH···O氢键的强度。这种影响可能是深远的:3,5-bis-CF 31,3-二恶烷中C(5)处的苯基对轴向方向显示