1H NMR spectral simplification with achiral and chiral lanthanide shift reagents--IV. Thiopental and barbiturate analogues.
The 60 MHz (1)H NMR spectra of racemic thiopental, 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, and tris[3-(heptafluoropropylhydroxymethylene)-d-camphorato] europium(III), 4. Enantiomeric shift differences, DeltaDeltadelta, were clearly observed for all three methyl signals of 1 with 3 or 4, with larger values obtained using the former reagent. Thus, a 0.216 molal solution of 1 in CDCl(3) at 28 degrees C with a 3:1 molar ratio of 0.359 displayed DeltaDeltadelta values of about 17 Hz for the proximal methyl of the methylbutyl group (at the chiral centre), 13 Hz for the CH(3) of the ethyl group, and 6 Hz for the distal CH(3) of the methylbutyl group. Results are compared for those obtained with 2 and 3 using secobarbital, talbutal, butabarbital and pentobarbital.
Eberhart
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The City University of New York, Toxicology Research and Training Center, John Jay College of Criminal Justice, Department of Science, 445 West 59th Street, New York, NY 10019-1199, USA.
Hatzis
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Jimenez
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Rothchild
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Simons
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