TRANS-CIS DIASTEREOROTAMERIZATION IN AMPHIPHILIC CHOLESTERIC LIQUID-CRYSTALS

Potassium hexadecanol-L-prolinate is investigated as a chiral dopant i n the formation of amphiphilic cholesteric liquid crystals with severa l achiral hosts. When the host is potassium laurate, the sense of heli cal twist is positive. When the host is potassium dodecanoyl-DL-alanin e or potassium tetradecanoyl-DL-alanine, the sense of helix twist is n egative. The apparent reversal in the helical twist sense is explained in of terms trans and cis diastereorotamers formed by hindered rotati on about the C-N amide link. C-13 NMR is used to determine the relativ e populations of these diastereorotamers, The twisting powers of these trans and cis rotamers were calculated using C-13 NMR population data to be -2000 +/- 200 and +250 +/- 20 cm(-1), respectively.