Library

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Theoretical study of the in-plane components of the 13C shielding tensors in condensed aromatic hydrocarbons (1987)
    Springer
    Theoretical chemistry accounts 71 (1987), S. 277-288 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF00529099
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Solid-state 13C NMR study of drugs: Aspirin (1986)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 24 (1986), S. 768-771 
    Details
    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
    URL: http://dx.doi.org/10.1002/mrc.1260240907
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Conformational analysis of DL-, L- and D-methionine by solid-state 13C NMR spectroscopy (1986)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 24 (1986), S. 167-170 
    Details
    ISSN: 0749-1581
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational analysis of DL-, L- and D-methionine was studied by solid-state 13C NMR with the help of cross-polarization and magic-angle spinning techniques. The spectrum of commercial crystalline DL-methionine showed two chemical shifts (18.7 and 15.8 ppm) for the methyl carbon. Crystallization from water or water-ethanol (95 : 5) allowed the separation of two crystalline forms (α and β), of which one had δ (CH3) 18.7 ppm and the other δ (CH3) 15.8 ppm. Therefore, each crystalline form of DL-methionine consists of a single conformer, a result in agreement with x-ray diffraction data. This conformational difference of the two crystalline forms was also reflected in the carbon resonances of C-β and C-γ. When L- and D-methionine were crystallized from water-ethanol (3 : 2), the solid-state 13C NMR spectra showed that each isomer displayed two methyl carbon peaks at 18.1 and 16.2 ppm of equal intensities, while the α-carbon resonances showed a broad peak due to two unresolved doublets. These results suggest that the L- or D-methionine crystal contains two different conformers in one unit cell, a conclusion that is also supported by the x-ray data.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260240213
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    The use of high-field carbon-13 NMR spectroscopy to characterize chiral centers in isopranes (1986)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 24 (1986), S. 191-198 
    Details
    ISSN: 0749-1581
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 13C nuclear magnetic resonance spectra of four diastereomeric, acyclic isoprenoids [farnesane (C15), pristane (C19), phytane (C20), and squalane (C30)] have been obtained as a means for interpreting hydrocarbon mixtures common in some fossil fuels and biosynthesized organic compounds. Multiple resonance environments were detected for carbons influenced by two or three chiral centers. Samples of farnesane and squalane were found to exhibit random stereochemistry, whereas the phytane sample was demonstrated to be a mixture of two isomers, probably the 6(R), 10(S), 14(R,S) compound. The sample of pristane consisted of a single diastereomer and was probably obtained from a natural product. It is shown that general chemical shift assignments can be made in this class of molecules by considering the number of carbons located at positions one, two and three bonds distant, while assignment of closely spaced lines may be made on the basis of diastereomerically induced chemical shifts. Using these principles, the structural features of two fossil fuels were analysed.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260240303
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...