Determination of the enantiomeric purity of disubstituted β‐lactams by NMR spectroscopy using a chiral shift reagent

The enantiomeric purities of disubstituted β‐lactams were determined by 1 H and 13 C NMR spectroscopy using tris[3‐(trifluoromethylhydroxymethylene)‐d‐camphorato]europium(III), Eu(tfc) 3 , as a chiral shift reagent. Using a [Eu(tfc) 3 ]/[lactam] ratio of 0.5, most of the resonances were split into signal pairs due to the respective enantiomers. The method gives quantitative enantiomeric compositions. 13 C NMR spectroscopy is more advantageous than 1 H NMR, which is of limited use owing, for example, to the significant line broadening observed in the 1 H spectra at [Eu(tfc) 3 ]/[lactam] > 0.8. Assignments of the proton and carbon signals were obtained for the two enantiomers of the complexed lactams.