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  • NH chemical shifts  (1)
  • β-diketones (five-membered ring)  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Deuterium isotope effects on 13C chemical shifts of intramolecularly hydrogen-bonded olefins (1995)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 33 (1995), S. 621-631 
    Details
    ISSN: 0749-1581
    Keywords: NMR ; 13C NMR ; isotope effects on 13C chemical shifts ; deuterium isotope effects ; intramolecular hydrogen bonding ; hydrogen bond strength ; olefins ; β-sulphinylenamines ; nitroenamines ; β-diketones (five-membered ring) ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of intramolecularly hydrogen-bonded enamines, enols and enethiols with ester carbonylic, ketonic carbonylic, thioester carbonylic, nitro and sulphoxide acceptors were investigated to obtain 13C chemical shifts and deuterium isotope effects. Results from 33 new compounds and six remeasurements are compared with already existing data. An important aim was to show that isotope effects on chemical shifts are useful descriptors of hydrogen-bonded systems and not only a parameter proportional to the 13C chemical shifts. Substituent effects were studied and the donors and acceptors ranked according to their abilities to support hydrogen bonding. Steric effects strengthen the hydrogen bonding in cyclic five-membered β-diketones. Plots of two-bond [2ΔC(OD)] vs. four-bond isotope effects [4ΔC(OD)] show that 4ΔC(OD) increases with increasing hydrogen bond strength and that large deviations from this relationship can be an indicator of tautomerism.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260330803
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  • 2
    Electronic Resource
    Electronic Resource
    Data for the characterization of the geometrical isomers of β-sulphinylenamines (1994)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 32 (1994), S. 517-524 
    Details
    ISSN: 0749-1581
    Keywords: β-Sulphinylenamines ; Geometrical isomerism ; NH chemical shifts ; Temperature effects ; 15N chemical shifts ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: NOE experiments at low temperature were used to establish the structure of the E- and Z-isomers of the enamine ButSOCH=CHNHBut. The NOE experiments revealed large intermolecular NOE effects between E- and Z-isomers indicating the formation of dimers of specific orientation. NH chemical shifts and their temperature dependence showed that the E- and Z- isomers behave differently. The NH chemical shifts of the former go to higher frequencies on lowering the temperature, whereas the opposite holds for the (Z)-NH resonance. Similar trends are found on increasing the concentration. The orientation around the C1—N bond can be probed by 3J(H1,NH) or by 1J(N,H). The 15N chemical shifts were also investigated in a series of β-sulphinylenamines. They are mainly dominated by α- and β-effects and show only a slight dependence on the E/Z isomerism, which seems to indicate a weak hydrogen bond in the Z-isomer at high concentration. Pertinent NMR parameters are now available for a general structure determination of geometrical isomers of β-sulphinylenamines.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260320904
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