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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 71 (1987), S. 277-288 
    ISSN: 1432-2234
    Keywords: Shielding tensors ; MNDO ; Bond orders ; Aromaticity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The Pople model for chemical shielding is applied to calculate the in-plane components of the 13C shielding tensors of condensed aromatic hydrocarbons. The wave functions are evaluated using the MNDO method and the calculated results are supported by the very good agreement with the experimental results in the few cases in which experimental information is available. The relationship found between the calculated bond orders and the in-plane components of the 13C shielding tensors suggest that the experimental study of the 13C shielding tensors in these compounds may provide a powerful technique for studying aromaticity. The in-plane components are found to be directly affected by the degree of delocalization of the π-electrons in the adjacent bonds. Rules are given for estimating the orientation of the two in-plane components of the shielding tensor.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 24 (1986), S. 768-771 
    ISSN: 0749-1581
    Keywords: Solid-state ; 13C NMR ; Aspirin ; Drugs ; Polymorphism ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Natural abundance 13C NMR spectra of different crystal habits of pure aspirin and several aspirin tablets in the solid state have been measured by using the combined techniques of high-power decoupling, cross-polarization and magic angle spinning. Solid-state NMR of aspirin had excellent sensitivity compared with liquid-state NMR, and the carbon signals were assigned using a modified pulse sequence to detect non-protonated carbons. The solid-state 13C NMR spectra of two crystalline forms of aspirin were identical, suggesting that the origin of their difference is not polymorphic.The solid-state 13C NMR spectra of several commercial aspirin tablets, some of them containing buffer components, indicated that there were no interactions among the aspirin and the buffer components; only after dissolving the tablets and lyophilization did the 13C NMR spectra of the dry lyophilized powders show strong interactions between aspirin and the buffer components.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 33 (1995), S. 803-811 
    ISSN: 0749-1581
    Keywords: NMR ; 13C NMR ; 2D INADEQUATE ; polycyclic benzenoid aromatics ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A computerized analysis of a single 2D INADEQUATE spectra assigns all of the 13C chemical shifts in fairly complex aromatic systems. Without the aid of the computer this information is often difficult, if not impossible, to retrieve owing to overlap of the signals in the double quantum dimension. In addition, the use of the computerized analysis allows for the interpretation of INADEQUATE spectra with much lower signal-to-noise ratios than are practical if the analysis were to be done visually. Finally, narrowing the spectral window to a subset of the entire spectrum and the companion advantages are demonstrated. The assignments of the aromatic chemical shifts in 2-methoxydibenzofuran, 6-methylchrysene, 1-decylpyrene, and 7-methylbenzo[a]pyrene illustrate the power of automated pattern recognition methods while supplying previously unavailable chemical shift assignments on these complex fused polycyclic aromatic systems.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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