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Applications of NMR spectroscopy of chiral association complexes 5. Stereodynamics and diastereotopism in chiral 1,3-dienes

✍ Scribed by Georg Becher; Thomas Burgemeister; Hans-Helmut Henschel; Albrecht Mannschreck

Publisher
John Wiley and Sons
Year
1978
Tongue
English
Weight
484 KB
Volume
11
Category
Article
ISSN
0749-1581

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✦ Synopsis

The barriers to partial rotation around the central single bond in chiral dieties HOCMe2(CCI=CC&X have been determined by coalescence of either 'H NMR signals (X=CH,OCH,) or 13C NMR signals (X=H). In the presence of the optically active shift reagent (+)-Eu(hfbc), all ' H signals were split at temperatures where the interconversion of enantiomers is slow. The temperature dependence of these spectra also yielded free activation enthalpies for the enantiomerizations which were in agreement with the ones obtained without Eu(hfbc),. The assignment of the four methyl resonances appearing in the presence of (+)-E~(hfbc)~ at low temperature was possible by gradually increasing the rate of enantiomerization or gradually replacing the optically active auxiliary compound by the racemic one.

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