Analysis of the stereodynamics of 2,2′-disubstituted biphenyls by dynamic chromatography

In contrast to 2,2′-diisopropylbiphenyl, 2-phenyl-2′-isopropylbiphenyl, 1, and 2-cyclohexyl-2′-phenylbiphenyl, 2, undergo racemization at room temperature. Chiral HPLC analysis on Chiralcel OD show formation of a temperature-dependent plateau between the well-resolved peaks due to simultaneous enantioseparation and on-column enantioconversion. The rotational energy barrier of these axially chiral compounds has been determined as 91.3 (1) and 91.4 kJ/mol (2) by computer simulation of experimentally obtained HPLC elution profiles.