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Optical Purity Determination and 1H NMR Spectral Simplification with Lanthanide Shift Reagents III: Ethotoin, 3-Ethyl-5-Phenyl-2, 4-Imidazolidinedione
Volume 38, Number 5 (Oct. 1984) Page 734-737
Avolio, John; Rothchild, Robert
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-dimethyl-3,5-octanedionato) europium (III), b, and the chiral tris[3-(trifluoromethylhydroxymethylene)-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 0.45 molal in a. Optical purity assays should be feasible with the use of the NH or CH3 absorptions that display ΔΔδ of 22.4 and 7.0 Hz, respectively, at a c:a molar ratio of about 0.3, with the former resonance being optimal. With a c:a ratio between 0.4-0.5, 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.