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  • Organic Chemistry  (2)
  • 1D-INADEQUATE  (1)
  • Quadrupole splitting constant  (1)
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Keywords
Publisher
Years
  • 1
    Electronic Resource
    Electronic Resource
    A Comparative 1H- and 13C-NMR Study of the Dianion and Dication of Biphenylene (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 955-961 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Biphenylene dianion has been prepared by Li reduction of the parent hydrocarbon. It is stable below -30° and was characterized by its 1H- and 13C-NMR spectra. A comparison of these data with those of the dication indicates the existence of ion pairs in the dianion case which are responsible for a different charge distribution. The diamagnetic ring currents of both ions, however, are of comparable magnitude, and both are more diatropic than the parent hydrocarbon. Predictions of the π-charge-density effect on 1H chemical shifts are improved by calculations that use the linear and quadratic electric-field effect equation instead of the simple Spiesecke-Schneider relation.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19860690502
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  • 2
    Electronic Resource
    Electronic Resource
    Solvation of indenyllithium and indenylpotassium studied by 13C NMR spectroscopy (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 9-12 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Polarization of the π-electron systems of indenyllithium (In -Li+) and indenylpotassium (In -K+), which is generally indicative of the degree and tightness of contact ion pairing, was investigated by 13C NMR spectroscopy. The effect of changing solvent is about two thirds as great for In -K+ as for In -Li+. The indenyl anion is more strongly polarized with Li+/dimethyl sulfoxide than with Li+/ammonia, whereas the reverse is observed for In -K+. Complexation of In -K+ in tetrahydrofuran (THF) by cryptand(2,2,2) results in a π-electron distribution identical with that of In -Li+ in hexamethylphosphoramide, indicative of solvent- or agent-separated ion pairs or free ions. Small but significant cation-anion interactions are observed for In -K+ in hexamethylphosphoramide and for In -N+Me4 in THF.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030103
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  • 3
    Electronic Resource
    Electronic Resource
    Natural abundance one-bond 13C—13C coupling constants and unambiguous assignments of 13C NMR chemical shifts of dithieno[b,d]pyridines; a multivariate data analysis (1990)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 28 (1990), S. 33-41 
    Details
    ISSN: 0749-1581
    Keywords: Dithieno[b,d]pyridines ; 13C NMR ; 1D-INADEQUATE ; Multivariate data analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The one-bond 13C—13C coupling constants (1JCC) in all nine possible dithieno[b,d]pyridines were measured at natural isotope abundance by using the INADEQUATE pulse sequence technique. The unambiguous assignments of the 13C NMR shifts of these compounds are also reported. Assignments are based on proton decoupled 13C spectra, heteronuclear correlation spectra (HETCOR) and 1D-INADEQUATE 13C NMR spectroscopy. The effect of the fusion pattern and the influence of the heteroatoms in the ring skeleton on the NMR parameters are discussed. By a multivariate principal components data analysis, it was shown that the magnitude of 1J(CC) of the pyridine subunit could be satisfactorily predicted from shift data, the azomethine C—H coupling constant and MNDO bond orders. The last parameter gave only a minor contribution to the coupling variability.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260280108
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  • 4
    Electronic Resource
    Electronic Resource
    13C, 6Li and 7Li NMR T1 and T1ρ study of ion-pair dynamics and structure of lithium fluorenide (1991)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 29 (1991), S. 1012-1017 
    Details
    ISSN: 0749-1581
    Keywords: 13C NMR ; 7Li NMR ; Rotating frame relaxation ; Ion-pair exchange ; Ion-pair structure ; Quadrupole splitting constant ; Lithium fluorenide ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rate of interconversion between tight and loose ion pairs of lithium fluorenide in 2-methyltetrahydrofuran was determined from 7Li relaxation in the rotating frame. The rate constant for the tight to loose ion-pair interconversion at -60°C is 2.3 × 104 s-1 and for the reverse process 2.6 × 103 s-1. The 13C relaxation times (T1) of the fluorenyl anion, adjusted for viscosity changes, do not change significantly with the ion-pair structure. The electric quadrupole relaxation contribution to the 7Li T1 was derived from 6Li and 7Li T1 measurements. Lower limits of 7Li quadrupole splitting constants (QSCs) were obtained from the 7Li quadrupolar and the 13C dipole-dipole relaxation times. The QSC values are in the range 37-200 kHz and appear to reflect changes in the ion-pair structure, with a low value corresponding to a solvent-separated ion pair. The higher value for the contact ion pair is in agreement with a structure where the anion disrupts the symmetrical coordination of solvent molecules around the cation. A decreased QSC and a shortened 13C T1 at high temperature for the diethyl ether solution may be caused by aggregation.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260291007
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