1H NMR Spectral Simplification with Achiral and Chiral Lanthanide Shift Reagents. Fenimide. Direct Simultaneous Determination of Four Stereoisomers

Abstract

Abstract The 60 MHZ 1H NMR spectra of racemic commercial fenimide, 4-ethyl-3-methyl-3-phenyl-2,5-pyrrolidine-dioner 1, have been studied in CDCl3 solution at 28° with the achiral shift reagent, tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato) europium-(III) 2, and the chiral reagent, trist3-(heptafluoro-propylhydroxymethy1ene)-d-camphoratol europium(III) 3. Use of 2 substantially increased the chemical shift differences between resonances of corresponding nuclei in the alpha and beta diastereomers, simplifying mixture analyses. Use of the chiral 3 produced enantiomeric shift differences, ΔΔΔ for several signals of 1. In particular, with a 0.309 molal solution of 1 and a 3:1, molar ratio near 0.4, four distinct singlets can be seen for the quaternary methyl signal. Direct simultaneous analysis for all four stereoisomers (two pairs of enantiomers) should be feasible.