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Variable-Temperature Study of Hydrogen-Bond Symmetry in Cyclohexene-1,2-dicarboxylate Monoanion in Chloroform‑d
Ist Teil von
Journal of the American Chemical Society, 2014-03, Vol.136 (11), p.4355-4362
Ort / Verlag
United States: American Chemical Society
Erscheinungsjahr
2014
Quelle
Alma/SFX Local Collection
Beschreibungen/Notizen
The symmetry of the hydrogen bond in hydrogen cyclohexene-1,2-dicarboxylate monoanion was determined in chloroform using the NMR method of isotopic perturbation. As the temperature decreases, the 18O-induced 13C chemical-shift separations increase not only at carboxyl carbons but also at ipso (alkene) carbons. The magnitude of the ipso increase is consistent with an 18O isotope effect on carboxylic acid acidity. Therefore it is concluded that this monoanion is a mixture of tautomers in rapid equilibrium, rather than a single symmetric structure in which a chemical-shift separation arises from coupling between a desymmetrizing vibration and anharmonic isotope-dependent vibrations, which is expected to show the opposite temperature dependence.
Sprache
Englisch
Identifikatoren
ISSN: 0002-7863
eISSN: 1520-5126
DOI: 10.1021/ja500174y
Titel-ID: cdi_proquest_miscellaneous_1508941867
Format
–
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