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  • Analytical Chemistry and Spectroscopy  (15)
  • 1985-1989  (15)
  • 1
    Electronic Resource
    Electronic Resource
    14N NMR nuclear shielding and the electronic structure of dibenzo[1,3a,4,6a]tetrazapentalene (1989)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 27 (1989), S. 88-91 
    Details
    ISSN: 0749-1581
    Keywords: 14N NMR ; Nuclear shielding calculations ; Charge separation ; N-Heterocycles ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 14N NMR data and semiempirical molecular orbital calculations are reported for dibenzo-[1,3a,4,6a]tetrazapentalene (1). The 14N signals were assigned by means of the results of the molecular orbital calculations and measured relative signal widths. A comparison was made with results for some azolopyridines. A linear correlation was obtained between the nitrogen shieldings, expressed with respect to the bridging nitrogen atom, and the corresponding relative charge densities. Thus nitrogen nuclear shielding results provide a good estimation of electron charge distribution in these molecules. Compound 1 provides the first case in which the shielding of a pyridine-type nitrogen atom is greater than that of the indolizine-type nitrogen.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260270116
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  • 2
    Electronic Resource
    Electronic Resource
    15N-13C spin coupling as a probe of electronic structure in benzenediazonium ions: INDO - SOS - MO calculations and steric inhibition of resonance (1988)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 26 (1988), S. 960-962 
    Details
    ISSN: 0749-1581
    Keywords: 1J(15N13C) values ; para-Substituted benzenediazonium ions ; Resonance forms ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The magnitude of 1J(15N13C) in para-substituted benzenediazonium ions has been used to assess the importance of the several resonance forms contributing to the ground state of the ion. From a comparison of values observed in 4-nitro- and 4-dimethylamino-benzenediazonium ions and their respective 3,5-dimethyl derivatives, it is concluded that diazo-type structures are important only with strong electron-releasing substituents in the aromatic ring. INDO-SOS-MO calculations indicate that the large and negative Fermi contact term dominates this interaction.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260261104
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  • 3
    Electronic Resource
    Electronic Resource
    Structural studies on some mesoionic compounds using nitrogen NMR (1988)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 26 (1988), S. 1012-1014 
    Details
    ISSN: 0749-1581
    Keywords: Nitrogen NMR ; Mesionic compounds ; Structure determination ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1H, 13C, 14N and 15N NMR data are reported for two 1,2,3,4-oxatriazolium-5-thiolates and for two 1,2,3,4-thiatriazolium-5-olates. It is demonstrated that nitrogen NMR is the most sensitive technique for determining the structures of these mesoionic compounds; of particular significance is the N-2 chemical shift, which distinguishes between the presences of either oxygen or sulphur in position 1. Cyclic structures are confirmed for these compounds on the basis of the nitrogen chemical shifts.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260261113
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  • 4
    Electronic Resource
    Electronic Resource
    Effects of solute-solvent interactions on the nitrogen nuclear shieldings of some alkyl cyanides (1989)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 27 (1989), S. 380-385 
    Details
    ISSN: 0749-1581
    Keywords: Nitrogen nuclear shieldings ; Alkyl cyanides ; Solute-solvent interactions ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It was found that the range of solvent effects on the nitrogen NMR shielding of the cyano group appears to be almost independent of the nature of the attached alkyl group and to be in excess of 20 ppm. Effects due to both the polarity of the medium and hydrogen bonding are observed to contribute almost equally to the nitrogen shielding ranges measured for four alkyl cyanides. These contributions are determined from the shielding in nitrogen variations with the solvent by means of a four-parameter model and are supported by molecular orbital calculations employing the solvaton description of non-specific solute-solvent interactions. The observed responses of the nitrogen shieldings to solvent effect are found to be significantly different from those reported for sp2-type nitrogen atoms.
    Additional Material: 8 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260270415
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  • 5
    Electronic Resource
    Electronic Resource
    M. Goldman. Quantum description of high-resolution NMR in liquids. Oxford University Press, 1988. £35.00 (1989)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 27 (1989), S. 507-507 
    Details
    ISSN: 0749-1581
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260270519
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  • 6
    Electronic Resource
    Electronic Resource
    A theoretical and empirical approach to solvent effects on nitrogen nuclear shielding (1985)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 23 (1985), S. 748-753 
    Details
    ISSN: 0749-1581
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Solvent effects on nitrogen shieldings are shown to vary from almost zero to about 26 ppm. These shielding variations can be analysed in terms of a variety of hydrogen bonding interactions and non-specific solute-solvent interactions. Steric effects are also taken into account. The non-specific interactions are found to be well accounted for by INDO/S-SOS shielding calculations incorporating the solvaton model. Nitrogen NMR is shown to be very suitable for distinguishing between a variety of solute-solvent interactions.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260230914
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  • 7
    Electronic Resource
    Electronic Resource
    Some aspects of high-pressure NMR (1986)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 24 (1986), S. 557-567 
    Details
    ISSN: 0749-1581
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Recent advances in the field of high-resolution NMR spectroscopy in both pure liquids and solutions, under high pressure, are reviewed. Experimental techniques employed for making the NMR measurements at high pressures are discussed. An overview of high-pressure NMR studies as applied to intramolecular dynamics, structures of liquids, molecular conformations and intermolecular interactions is presented.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260240702
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  • 8
    Electronic Resource
    Electronic Resource
    NMR studies of phosphonate carbanions: Influence of substituents on 1J(PC) and 1J(CH) and some INDO calculations (1985)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 23 (1985), S. 48-51 
    Details
    ISSN: 0749-1581
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 13C and 31P NMR data are reported for a series of phosphonate carbanions. In comparison with related uncharged molecules, the values of 1J(PC) are rather large. This is discussed with the help of some INDO-SCPT spin-spin coupling calculations, which reveal that while the positive contact term makes the dominant contribution to these couplings, the negative orbital term also plays an important role. The signs of 1J(PC) and 1J(CH) are predicted to be positive in all cases. Support for the proposal of a planar anionic carbon atom is forthcoming from the INDO-SCPT calculations.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260230113
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  • 9
    Electronic Resource
    Electronic Resource
    Applications of 15N NMR to a study of tautomerism in some monocyclic azoles (1985)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 23 (1985), S. 166-169 
    Details
    ISSN: 0749-1581
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 15N NMR shielding measurements reveal that thiolo-imidazole and -tetrazole exist almost entirely as the thione form. Quantitative estimates of the position of tautomerism in 1,2,3-triazole and tetrazole are obtained. The reported assignments are supported by means of INDO/S-SOS shielding calculations.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260230307
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  • 10
    Electronic Resource
    Electronic Resource
    15N NMR studies of the tautomeric equilibrium of some 1-hydroxybenzotriazoles (1985)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 23 (1985), S. 181-184 
    Details
    ISSN: 0749-1581
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By means of 15N NMR shielding measurements it is possible to obtain quantitative results on tautomeric equilibria for N-hydroxybenzotriazole and its 4- and 6-mononitro derivatives. For the unsubstituted compound the position of the tautomeric equilibrium is found to depend on the pKa value of the solvent. Intramolecular hydrogen bonding appears to be responsible for an increase in the proportion of the N-oxide form present in the equilibrium mixture of the 4-mononitro compound.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260230310
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