The absolute structures of separated PCB-methylsulfone enantiomers determined by vibrational circular dichroism and quantum chemical calculations

Four chiral transformation products of polychlorinated biphenyls (PCBs), the most prevalent methylsulfonyl-PCBs (MeS2-PCBs) 3-MCSO2-2,2',4',5,5',6-hexachlorobiphonyl (3-149), 3-MeSO2-2,2',3',4,5,5,6-heptachlorobiphenyl (3-174), 3-MeSO2-2,2',3',4',5,6-hexachlorobiphenyl (3-132), and 4-MeSO2-2,2',3,3,4,6-hexachlorobiphenyl (4-132), were separated into their enantiomers, in order to determine the absolute configuration of these enantiomers using vibrational circular dichroism (VCD) complemented by quantum chemical ab initio calculations (QC). In all four derivatives, the angles between the planes of the two phenyl rings range between 88 and 90degrees, i.e. the rings attain a nearly perpendicular conformation to each other. Furthermore, the methyl sulfonyl groups are also directed almost perpendicular to the respective phenyl ring directly connected to this substituent. VCD spectroscopy in conjunction with QC is probably the only experimental approach that can yield the absolute configuration of relatively complex chiral molecules such as the enantiomers of MeSO2-PCB, for which it is almost impossible to obtain suitable single crystals for XRD experiments. (C) 2002 Elsevier Science B.V. All rights reserved.