Trans−Cis Diastereorotamerization in Amphiphilic Cholesteric Liquid Crystals

Abstract

Potassium hexadecanoyl-l-prolinate is investigated as a chiral dopant in the formation of amphiphilic cholesteric liquid crystals with several achiral hosts. When the host is potassium laurate, the sense of helical twist is positive. When the host is potassium dodecanoyl-dl-alanine or potassium tetradecanoyl-dl-alanine, the sense of helix twist is negative. The apparent reversal in the helical twist sense is explained in of terms trans and cis diastereorotamers formed by hindered rotation about the C−N amide link. 13C NMR is used to determine the relative populations of these diastereorotamers. The twisting powers of these trans and cis rotamers were calculated using 13C NMR population data to be −2000 ± 200 and +250 ± 20 cm-1, respectively.