The biphenyl-monitored effective size of unsaturated functional or fluorinated ortho substituents
作者:Renzo Ruzziconi、Sara Spizzichino、Andrea Mazzanti、Lodovico Lunazzi、Manfred Schlosser
DOI:10.1039/c0ob00136h
日期:——
cyano groups were found to be slightly smaller than a phenyl ring. In contrast, vinyl and, in particular, formyl groups proved to be larger than phenyl. The latter difference is due to the loss of conjugation forces at the planar transition state. α-Hydroxyhexafluoroisopropyl is slightly more bulky than tert-butyl. Pentafluorophenyl and trifluoromethoxy exhibit nearly the same effective size as phenyl
一系列典型取代基的大小已通过动态NMR测量,对相应联苯的芳基-芳基旋转势垒进行了探测。所结果的乙该值是有意义的,因为仅研究了单-邻位取代的化合物,因此多重空间效应的不加和性不会损害结果。根据所选的模型系统乙炔基发现氰基和氰基略小于苯环。相比之下,乙烯基塑料尤其是甲酰基被证明比苯基大。后者的差异是由于在平面过渡状态下共轭力的损失。α-羟基六氟异丙基比叔丁基略大。五氟苯基 和 三氟甲氧基分别具有与苯基和甲氧基几乎相同的有效尺寸。三氟甲基略小于异丙基。