Poly-7-benzyl-L-glutamate (PBLG) and dichloromethane form a lyotropic liquid crystal which can be used as solvent for enantiomeric excess analysis of molecules containing several stereogenic centers, through deuterium NMR spectroscopy. All isomers of 3-deuterio-2methylcyclohexanone and of 3-deuterio-2-methylcyclohexanol dissolved in PBLG/CH2C12 solvents, exhibit different quadrupolar splittings on their deuterium NMR spectra, which allows an accurate determination of their diastereoisomeric and enantiomeric excesses.
We have recently reported that dichloromethane solutions of poly-'g-benzyl-L-glutamate (PBLG), which forms a lyotropic liquid crystal, can be used as a chiral deuterium NMR solvent to distinguish enantiomers l. The discrimination originates from the fact that, in such an anisotropic chiral medium, two enantiomers exhibit different averaged molecular ordering parameters. This phenomenon is expressed in a deuterium NMR spectrum, in different values of quadrupolar splitting for each enantiomer.
We have recorded proton decoupled deuterium NMR spectra of cyclohexanone 2 and cyclohexanol 3 -in racemic and optically active forms -dissolved in PBLG/CH2C12 solvent 2, in order to see if the differences in the quadrupolar splittings between all isomers could be important enough to measure accurately their diastereoisomeric and enantiomeric purifies.