Restricted Rotation Involving the Tetrahedral Carbon. XLVII. The “Positive” and the “Negative” Buttressing Effects on the Rotational Barriers in 9-(1,1-Dimethyl-2-phenylethyl)-1-halotriptycenes
作者:Gaku Yamamoto、Masahiko Suzuki、Michinori Oki
DOI:10.1246/bcsj.56.809
日期:1983.3
9-(1,1-Dimethyl-2-phenylethyl)-1,2,3,4-tetrahalotriptycenes (halogen=F, Cl, and Br) were synthesized and the kinetic studies of the rotational isomerization were made. The obtained data were compared with those for the corresponding 1-halo derivatives. The equilibrium constants (±sc⁄ap) for the tetrahalo compounds are smaller than those for the respective monohalo counterparts. The tetrafluoro compound isomerizes twice slower than the monofluoro one at 240 °C, showing the “positive” buttressing effect. Contrarily, the tetrachloro and the tetrabromo compounds isomerize 13 and 100 times, respectively, faster than the corresponding monohalo compounds at 175 °C, exhibiting the “negative” buttressing effect. These intriguing phenomena are discussed in terms of the molecular deformation in these congested compounds, which affects both the ground state and the transition state for rotation.
合成了9-(1,1-二甲基-2-苯乙基)-1,2,3,4-四卤三蝶烯(卤素=F、Cl、Br)并进行了旋转异构化动力学研究。将获得的数据与相应的1-卤代衍生物的数据进行比较。四卤代化合物的平衡常数 (±sc⁄ap) 小于相应单卤代化合物的平衡常数。在 240 °C 时,四氟化合物的异构化速度比一氟化合物慢两倍,显示出“积极”的支撑效应。相反,在175℃下,四氯和四溴化合物的异构化速度分别比相应的单卤代化合物快13倍和100倍,表现出“负”支撑效应。这些有趣的现象是根据这些拥挤的化合物中的分子变形来讨论的,这会影响旋转的基态和过渡态。