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.
研究人员合成了 1,4-二甲基-9-苯氧基三
联苯及其衍
生物,这些衍
生物在苯氧基的邻位上带有甲基、异丙基或叔丁基,并研究了它们的动态核磁共振行为。这些分子被认为构成了一个具有双齿和三齿齿轮的锥齿轮系统,其动态核磁共振行为最好用齿轮旋转来解释。例如,邻异丙基衍
生物的 ap\ightleftharpoons±sc 和 +sc\ightleftharpoons-sc 齿轮转动过程的能垒分别为 17.2 和 10.8 kcal mol-1。随着邻烷基的体积增大,±sc 转子的数量也随之增加:邻烷基、氧原子和过甲基之间的立体拥塞在 ap 中比在±sc 中严重。本文讨论了这些分子的分子力学计算结果。