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

The synthesis and H-1 NMR spectra are presented for diastereoisomeric ester s based on chiral alpha-chloro acids which are derived from natural availab le alpha-amino acids (L-valine, L-leucine and L-isoleucine) and commonly em ployed 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 esterifica tion procedure. The enantiomeric excess exceeds 90% for L-isoleucine and L- valine derivatives, whereas an enantiomeric excess of 60% is found for L-le ucine derivatives. On the basis of existing data in the literature, the dif ferences 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.