Optical Purity Determination, Conformer Populations, and 1H NMR Spectral Simplification with Lanthanide Shift Reagents. Part VII: 3,4-Methylenedioxyamphetamine (MDA)

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The 60 MHz 1H NMR spectra of racemic 3,4-methylenedioxyamphetamine (MDA), 1, 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), 2, and the chiral tris[3-(trifluoromethylhydroxymethylene)- d-camphorato]europium (III), 3. Moderate values of the enantiomeric shift difference, ΔΔδ, were observed for each of the benzylic protons and the CH3, with the use of added 3 in CDCl3 solutions at 28°C. The CH3 resonance was analytically useful for direct optical purity assays; as little as 3% of the minor enantiomer should be detectable. The (+)-isomer of 1 had its CH3 absorption at higher field in spectra shifted by 3. Appropriate peak height measurements were determined for best accuracy in optical purity assays. The relative abundances of the different conformers with respect to Cα-Cβ bond rotation based on coupling constants in the CH2CH moiety are discussed.