CONFORMATIONAL AND CONFIGURATIONAL ANALYSIS OF 4,4'-BIPHENANTHRYL DERIVATIVES AND RELATED HELICENES BY CIRCULAR-DICHROISM SPECTROSCOPY AND CHOLESTERIC INDUCTION IN NEMATIC MESOPHASES

Coupling the analysis of circular dichroism (CD) spectra with the stud y of cholesteric mesophases induced in nematic liquid crystals (LC) al lows one to deduce some stereochemical features of 3,3'disubstituted-4 ,4'-biphenanthryl derivatives. The exciton coupling model can explain the CD spectra of the open-chain derivatives, thus confirming their ab solute configuration; the LC technique indicates an s-trans conformati on in agreement with molecular mechanics computations. Compounds with a bridge between the 3 and 3' positions are conformationally rigid and similar in shape, and their absolute configuration can be predicted b y the LC technique. On the other hand, their CD spectra are different and not easy to interpret as a consequence of the different chromophor es present.