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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
    ISSN: 0749-1581
    Keywords: Alphitonia zizyphoides ; Saponin ; 2D NMR ; INADEQUATE ; Molecular structure ; Computerized spectral analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: High-field NMR experiments, including the 2D INADEQUATE technique coupled with a computerized spectral analysis, were used to determine the full structure of a new saponin extracted from a plant (Alphitonia zizyphoides) found in the Samoan rain forests. The saponin, which shows significant pharmacological activity, consists of an aglycone framework of six rings (three saturated six-membered rings, two oxygen-containing five-membered rings and a five-membered carbon ring) to which are attached four sugar units and a six-carbon side-chain. The INADEQUATE experiment, which was carried out on 60 mg of sample, provided absolute confirmation of the assignments for 35 of the possible 53 C—C bonds from the 13C-13C connectivities.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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