Determination of the enantiomeric excess of ferroelectric liquid crystals derived from three natural amino acids

Abstract

The synthesis and 1H NMR spectra are presented for diastereoisomeric esters based on chiral alpha-chloro acids which are derived from natural available alpha-amino acids (L-valine, L-leucine and L-isoleucine) and commonly employed for the synthesis of ferroelectric liquid crystals possessing a high spontaneous polarization. Partial racemization is established as occurring within the formation of the chiral alpha-chloro acids and their esterification procedure. The enantiomeric excess exceeds 90% for L-isoleucine and L-valine derivatives, whereas an enantiomeric excess of 60% is found for L-leucine derivatives. On the basis of existing data in the literature, the differences in the spontaneous polarization of these derivatives is discussed with regard to the determined enantiomeric excess and their conformational freedom affecting the average lateral dipole moment of a single molecule.