Rotational Isomerism and Atropisomerism in Acetal Derivatives of 1,2,3,4-Tetrafluorotriptycene-9-carbaldehyde
作者:Gaku Yamamoto
DOI:10.1246/bcsj.65.1967
日期:1992.7
In the ethylene acetal (2) of 1,2,3,4-tetrafluorotriptycene-9-carbaldehyde, equal amounts of the ap and ±sc rotamers exist in CDCl3 at equilibrium, while the equilibrium is strongly shifted to ±sc in the corresponding dimethyl and trimethylene acetals. Molecular mechanics calculations reveal the origin of this anomaly to reside in the conformation of the acetal moiety. Dynamic NMR studies show that
在 1,2,3,4-四氟三苯乙烯-9-甲醛的乙缩醛 (2) 中,CDCl3 中存在等量的 ap 和 ±sc 旋转异构体,而平衡在相应的二甲基苯胺中强烈移动至 ±sc和三亚甲基缩醛。分子力学计算揭示了这种异常的起源在于缩醛部分的构象。动态 NMR 研究表明 ap → ±sc 势垒太低,无法在这些化合物中实现阻转异构(ΔG≠ ca. 21–22 kcal mol-1 (1 calth = 4.184 J))。然而,利用不寻常的平衡行为,通过从平衡的旋转异构体混合物的溶液中选择性结晶一个旋转异构体,将 2 的两个旋转异构体分离为晶体。