Restricted Rotation Involving the Tetrahedral Carbon. LIV. The Effects of 1-Substituents on the Barriers to Rotation in 9-(2-Methyl-1-naphthyl)fluorenes
作者:Shigeru Murata、Teruo Mori、Michinori Oki
DOI:10.1246/bcsj.57.1970
日期:1984.7
A series of 1-substituted 9-(2-methyl-1-naphthyl)fluorenes, where the substituent is fluoro, chloro, bromo, or methyl, has been prepared and barriers to rotation in these compounds have been examined to investigate the substituent effects. The barrier is enhanced generally, if we go from the 1-substituent of a small size to that of a large size with an exception of the fluorine case: the 1-fluoro compound exhibits a lower barrier to rotation than the unsubstituted compound by ca. 0.5 kcal mol−1. X-Ray crystallographic analysis suggests that, in the fluoro compound, the C9(fluorene)-to-C1(naphthalene) bond is abnormally long, although other compounds possess bonds of normal lengths. The low barrier to rotation in the fluoro compound relative to the unsubstituted is thus attributed to the raise of the ground state energy and insufficient raise of the transition state energy in the former compound.
制备了一系列1-取代的9-(2-甲基-1-萘基)芴,其中取代基为氟、氯、溴或甲基,并研究了这些化合物的旋转障碍以探讨取代基效应。通常,当我们从小尺寸的1-取代基转向大尺寸取代基时,旋转障碍会增强,但氟的情况除外:1-氟化合物的旋转障碍比未取代的化合物低约0.5 kcal mol−1。X射线晶体学分析表明,在氟化合物中,C9(芴)到C1(萘)的键异常较长,而其他化合物则具有正常长度的键。因此,氟化合物相对于未取代化合物较低的旋转障碍被归因于基态能量的提高和过渡态能量的不足提高。