OBSERVATION OF RESTRICTED ROTATION ABOUT C–O BONDS BY NMR SPECTROSCOPY IN 9-(2-ALKYLPHENOXY)TRIPTYCENES, A GEAR ROTATION SYSTEM
作者:Gaku Yamamoto、Michinori Oki
DOI:10.1246/cl.1984.97
日期:1984.1.5
4-dimethyltriptycenes revealed that, when the o-alkyl group is methyl or isopropyl, two conformers, ap and ±sc, are separately observed at room temperature and that the interconversion between them occurs by gear rotation with an energy barrier of ca. 18 kcal mol−1
9-(2-烷基苯氧基)-1,4-二甲基三萜烯的动态核磁共振研究表明,当邻烷基为甲基或异丙基时,在室温下分别观察到两个构象异构体 ap 和 ±sc,并且它们通过具有约能量势垒的齿轮旋转发生。18 kcal mol−1
Restricted Rotation Involving the Tetrahedral Carbon. LVII. Stereodynamics of 9-(2-Alkylphenoxy)-1,4-dimethyltriptycenes
作者:Gaku Yamamoto、Michinori Oki
DOI:10.1246/bcsj.58.1953
日期:1985.7
1,4-Dimethyl-9-phenoxytriptycene and its derivatives carrying a methyl, isopropyl, or t-butyl group in the o-position of the phenoxyl moiety were synthesized and their dynamic NMR behavior was studied. These molecules are considered to constitute a bevel gear system with a two-toothed and a three-toothed wheels and the dynamic NMR behavior is best explained in terms of gear rotation. The o-isopropyl derivative, for example, shows the energy barriers of 17.2 and 10.8 kcal mol−1 for the ap\ightleftharpoons±sc and +sc\ightleftharpoons−sc gearing processes, respectively. The population of the ±sc rotamer increases with the bulkiness of the o-alkyl group: The steric congestion among the o-alkyl group, the oxygen atom, and the peri-methyl group is severer in ap than in ±sc. Results of molecular mechanics calculations on these molecules are discussed.