Chemical Shift Nonequivalence of Enantiomers of Amino Acid Derivatives in ‘H NMR and 19F NMR Spectroscopy Induced by L-Chirasil- Val

Enantiomers o f N-trifluoroacetyl-amino acid methyl esters in CC14 solution, after addition of the chiral polysiloxane (L)-Chirasil-Val, display a chemical shift nonequivalence AA5 in both 'H NM R and l9F N M R spectroscopy. The effects found for the leucine and valine deriva­ tives can be correlated with the thermodynamic parameters o f interaction in the undiluted sys­ tem, as determined by gas chromatography. In CDC13 solution, no peak splitting was ob­ served. The method is potentially useful for the determination o f the enantiomeric purity o f substrates o f low volatility.