Restricted Rotation Involving the Tetrahedral Carbon. XV. Restricted Rotation about a Csp8–Csp2 Bond in 9-Aryltriptycene Derivatives

Abstract

Abstract A series of 9-aryltriptycene derivatives have been prepared and their internal rotation about the CAr–C9 bond has been examined by DNMR technique. The PMR behavior of these compounds is best interpreted by assuming a back and forth rotation rather than a full rotation. The barriers to rotation of compounds with one substituted benzo group have been found to be in the range 13–15 kcal/mol, whereas those with two substituted benzo bridges are lower than 9 kcal/mol. The low barrier of these compounds relative to 9-alkyltriptycenes is attributed to the rise in energy of the ground state. The stable conformation of the 9-aryltriptycenes is also discussed.