Optical purity determination, conformer populations and 1H NMR spectral simplification with lanthanide shift reagents — Part IX. A method for improved analytical precision for “DOEt”, 2,5-dimethoxy-4-ethylamphetamine

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The 60 MHz 1H NMR spectra of the potent hallucinogen 2,5-dimethoxy-4-ethylamphetamine (“DOEt”), 1, have been studied in CDCl 3 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 reagents tris[3-(trifluoromethylhydroxymethylene)- d-camphorato] europium(III), 3, and tris[3-(heptafluoropropylhydroxymethylene)- d-camphorato] europium(III), 4. Distinct enantiomeric shift differences, ΔΔδ, were observed for the amphetamine CH 3 and the adjacent CH resonances using either 3 or 4 that permit direct optical purity determinations. A novel use of an external computing integrator as an accessory to a basic NMR is described; interfacing these instruments permits improved analytical precision for the reported optical purity determinations using nonracemic mixtures of known compositions. Relative abundances of the different conformers with respect to C αC β bond rotation in the arylethylamine moiety is discussed based on coupling constants. Results are compared with the related hallucinogen, 3,4-methylenedioxyamphetamine.