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1 H‐NMR.‐spektroskopische Bestimmung der Enantiomerenreinheit von Allencarbonsäureestern mit optisch aktiven Europium‐Verschiebungsreagenzien
Author(s) -
Lang Robert W.,
Hansen HansJürgen
Publication year - 1979
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19790620413
Subject(s) - chemistry , enantiomer , substituent , europium , reagent , enantiomeric excess , proton nmr , medicinal chemistry , optically active , racemic mixture , stereochemistry , organic chemistry , enantioselective synthesis , catalysis , ion
1 H‐NMR. Spectroscopic Determination of Enantiomeric Purities of Allenic Esters Using Optically Active Europium Shift Reagents The racemic allenic methyl esters 3‐‐7 and the racemic allenic diesters 8‐‐10 ( cf. Scheme 2 ) in 1,1,2‐trichloro‐1,2,2‐trifluoroethane (TCFE) and CCl 4 in the presence of optically active tris[3‐(heptafluorobutyryl)‐(+)‐camphorato]europium(III) (Eu(hfc) 3 ) have induced unlike 1 H‐NMR. shift differences (ΔΔδ) for the protons of the methoxycarbonyl groups of their enantiomers. In some allenic esters the shift reagent causes additional separation of resonance signals; thus, further substituents on the allenic framework may be differentiated in the racemic mixture. This finding provides a widely applicable method for the determination of absolute enantiomeric purities of allenic esters and their corresponding acids. Accordingly we found for optically pure (+)‐( S )‐2‐methyl‐2,3‐pentadienoic acid ((+)‐( S )‐ 13 ; cf. Fig. 2 ) a calculated [α] 589 20value of + 73.3 ± 1.8°. Finally, the substituent effects on ΔΔδ‐values ( cf. Table 1‐‐3 ) are discussed.