CONFORMATIONAL-ANALYSIS OF SOME TRANS-4,5-DIARYL-1,3-DIOXOLANES BY CDSPECTROSCOPY AND INDUCTION OF CHOLESTERIC MESOPHASES IN NEMATIC SOLVENTS - A CORRELATION BETWEEN TWISTING POWER AND STRUCTURE OF THE DOPANT

A series of trans-4,5-diaryl-1,3-dioxolanes (compounds 1-10) has been prepared from the corresponding 1,2-diols obtained by asymmetric syn-d ihydroxylation of (E)-olefins, in the presence of derivatives of quini dine. Compounds 1-10, when dissolved in MBBA or E7, induce left-handed cholesterics, showing twisting powers which, in absolute value, are s trongly dependent on the structure of the solute and on the nature of the nematic mesophase. By means of molecular mechanics calculations an d the analysis of CD spectra of 1-10, it is possible to determine the most stable conformation of these derivatives which is characterized b y a negative twist of the aryl moiety. With this information a reliabl e cholesteric induction model has been developed.