Stereoisomers of hydrogenated triptycene: a joint crystallographic and conformation study of a set of strained hydrocarbon molecules

Abstract

A joint X-ray single-crystal and conformational (molecular mechanics) study has been carried out on several hydrogenated triptycene stereoisomers. The calculated and observed geometries compare quite satisfactorily. In particular the lowest-energy conformation of the cyclohexane rings cis-attached to the bicyclo-octane cage always coincides with the unusual boat-conformation. The free energy of the most stable perhydrotriptycene stereoisomers in the gaseous state, calculated neglecting vibrational entropy contribution, is also in good agreement with the equilibrium concentrations reached in solution after on month at 172 °C, in the presence of Pd/C catalyst.