Restricted Rotation Involving the Tetrahedral Carbon. LX. peri-Substituent Effect on the Rotational Barrier of the 9-Methyl Group in Several Trypticene Derivatives

Article abstract of DOI:10.1246/bcsj.63.3550

Dynamic 1H NMR study was made on several 1-substituted 8,13-dichloro-9-methyltriptycenes and 8-chloro-13-fluoro-9-methyltriptycenes to examine the effect of peri-substituents on the rotational barrier of the 9-methyl group.The rotational barrier height increases in the expected order as the 1-hydrogen is repleaced by a bulkier group up to CH3, but shows a very low value when a t-butyl group is introduced into 1-position to show that destabilization of the ground state by the bulky t-butyl group exceeds that of the transition state for rotation.