Restricted rotation involving the tetrahedral carbon .63. Endeavor toward enhancing the rotational barrier in 9-s-alkyltriptycenes

In order to enhance barriers to rotation about the C-9-substituent bond in 9-s-alkyltritpycenes the secondary alkyl group was modified as well as the peri-substituent. The barrier was slightly enhanced by modifying the substituents but the extent was rather limited. This limitation was attributed to the limitation of the ways of preparation of 9-s-alkyltriptycenes that should give three stable rotamers and carry substituents at peri-positions, where only 1,8-difluoro substituents could be used.