Rotational isomerism involving an acetylenic carbon. Part 5: Restricted rotation about acetylenic axis in sterically crowded bis (1-phenyl-9-anthryl) ethynes

摘要

The title sterically crowded di-9-anthrylethyne derivative with 3,5-~iPr_2-phenyl groups at 1-position showed a barrier to rotation about the acetylenic axis of 18.0 kcal mol~(-1) based on a dynamic NMR study, which is an extremely high value for acyclic diarylethynes. The mechanism of the dynamic stereochemistry and the substituent effect on the rotational barrier are discussed.