Isolation and characterisation of polychlorinated biphenyl (PCB) atropisomers

High-performance liquid chromatography on permethylated β-cyclodextrin derivatized silica was used to isolate enantiomers of stable atropisomeric polychlorinated biphenyls. The separations were performed in the reversed phase mode (85 % methanol) at subambient temperature (0°C). Several injection/fractionation cycles were performed for each atropisomer. In this way milligram quantities of pure (> 98%) enantiomers could be isolated. These enantiomers were characterised by polarimetry. The specific optical rotation seems to increase as the degree of chlorination decrease, e.g., PCB#196 (octachlorinated) and PCB#84 (pentachlorinated) exhibit a rotation of ca. 30 and 240 degree * ml * g−1 * dm−1, respectively (λ = 436 nm). Furthermore, the (−)-enantiomers always elute prior to the (+)-enantiomers. This implies that PCB atropisomers with similar spatial conformation have similar optical rotation properties.