Complex stereochemistry First, researchers from Empa and ETH Zurich revealed that technical HBCD is in fact a mixture of at least eight different stereoisomers. Stereoisomers are substances which have the same chemical composition, yet differ in the spatial arrangement of their atoms. Six of the eight stereoisomers possess distinct mirror images: they are chiral and relate to each other just as the right hand does to the left. In the case of two other stereoisomers, however, one form and its mirror image are identical. Here we speak of meso compounds: such molecules have stereocenters but are nevertheless achiral. Heeb and his colleagues concluded early on that individual stereoisomers may differ not only in their three-dimensional structure, but also in their toxicity and their environmental behaviour. This has since been confirmed by other research groups. Empa's work on flame-proofed polystyrenes has also shown that even while materials are being processed, HBCDs can transform into hitherto unknown and also potentially toxic derivatives. |