The Barrier to Rotation in 9,10-Bis(2,3-dimethylphenyl)phenanthrene: Conformational Interconversion Observed at High Temperatures by Means of Gas Chromatography

Abstract

A mixture of the syn and anti conformers of 9,10-bis(2,3- dimethylphenyl ) phenanthrene was prepared. The unexpectedly high energy barrier for the free rotation of the two aryl rings is described. Variable temperature ¹H n.m.r . studies failed to provide thermodynamic data for the conformational inter-conversion due to limitations in practicably measurable temperature range. The energies of activation for both interconversion processes were, however, determined by gas chromatographic studies in the temperature range of 225-300°C.