Why Are Silyl Ethers Conformationally Different from Alkyl Ethers? Chair−Chair Conformational Equilibria in Silyloxycyclohexanes and Their Dependence on the Substituents on Silicon. The Wider Roles of Eclipsing, of 1,3-Repulsive Steric Interactions, and of Attractive Steric Interactions
作者:Cecilia H. Marzabadi、J. Edgar Anderson、Jorge Gonzalez-Outeirino、Piers R. J. Gaffney、Christopher G. H. White、Derek A. Tocher、Louis J. Todaro
DOI:10.1021/ja035936x
日期:2003.12.1
An NMR study of the diaxial/diequatorial chair equilibrium in a range of silylated derivatives of trans-1,4- and trans-1,2-dihydroxycyclohexane is reported and discussed with a view to explaining unusually large populations of chair conformations with axial substituents, noted previously for some monosilyloxycyclohexanes and in some silylated sugars. X-ray diffraction studies of three bis-tripheny
报道并讨论了一系列反式-1,4-和反式-1,2-二羟基环己烷的甲硅烷基化衍生物中的双轴/双正交椅平衡的核磁共振研究,以解释异常大量的具有轴向取代基的椅构象,之前针对某些单甲硅烷氧基环己烷和某些甲硅烷基化糖进行了说明。报告了三种双三苯基甲硅烷氧基环己烷的 X 射线衍射研究,结果显示轴向和赤道甲硅烷氧基都带有环外键。对此类衍生物的分子力学 (MM3) 计算也建议了日食。轴向和赤道叔甲硅烷基与位于两个相邻赤道位置的任何取代基或氢原子都具有 1,3-排斥相互作用,这些通过向环外 CO 键的重叠构象旋转而减轻。硅上的三个取代基与环己烷环的 3、4 和 5 位上的九个原子有吸引力地相互作用,计算表明这些稳定相互作用在轴向上明显大于在赤道构象中。与一个或两个赤道邻居的赤道 C-OSiR(3) 键具有有限的势能阱,当键是轴向的时,替代椅子上没有任何赤道邻居时,势能井变得更宽。1,2-二取代系列中相邻的甲硅