Optical Purity Determination and 1 H NMR Spectral Simplification with Lanthanide Shift Reagents III: Ethotoin,3-Ethyl-5-Phenyl-2,4-Imidazolidinedione

The 60 MHz ¹H NMR spectra of racemic ethotoin, a, have been studied with the achiral shift reagent tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimeth-yl-3,5-octanedionato) europium (III), b, and the chiral tris[3-(rrifluoromethylhydroxymethylene)-d-camphorato] europium (III), c Appreciable values of the enantiomeric shift difference, ΔΔδ, were observed for the NH, CH₃, CH, and ortho aryl protons in CDCl₃ solutions at 28°C with the use of samples about 045 molal in a Optical purity assays should be feasible with the use of the NH or CH₃ absorptions that display ΔΔδ of 224 and 70 Hz, respectively, at a c:a molar ratio of about 03, with the former resonance being optimal With a c:a ratio between 04–05, the methine proton can be used, with ΔΔδ 11 – 13 Hz Results are interpreted in terms of major coordination of the europium at the C-2 oxygen