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  • 1
    Electronic Resource
    Electronic Resource
    Effect of the substituents on the conformational behavior of five-membered rings: Application to the cis- and trans-2,5-dimethoxytetrahydrofuran (1988)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 9 (1988), S. 189-199 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A model is proposed which assumes that the pseudorotational potential in five-membered rings is given by the combination of contributions from the unsubstituted ring, from the individual substituents and from interactions between pairs of substituents. The application of this model to the potentials calculated by the MM2 force field for the cis and trans-2,5-dimethoxytetrahydrofuran shows that the contributions from the individual substituents explain the main features of the potentials of these disubstituted rings. The pseudorotational analysis from vicinal proton spin-spin coupling constants 3JHH confirms the realibility of the MM2 potentials.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540090302
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Long-Range proton-proton coupling constants. I. Propanic coupling involving a methyl group 4JMeH (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 10 (1989), S. 887-895 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: An equation is formulated on the basis of theoretical INDO/FPT calculations which describes the angular dependence of the propanic long-range coupling constant 4JMeH in substituted HCCCH3 fragments. This equation is a truncated Fourier series in the torsion angle φ, HCCMe, which takes into account the dependence of the Fourier coefficients on the bond angle θ, CCMe. The substituent effects are assumed to be additive. Some parameters in the equation may be obtained from the 4JMeH couplings in propane and neopentane derivatives. The calculated effect upon 4JMeH of changes in the bond angle θ is significant and it seems to be in part the cause of some effects which have been attributed to conformational dependence.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540100705
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Methoxy group conformation effects on 13C NMR parameters in 1-cis-methoxy- and 1-trans-methoxy-1,3-trans-butadiene (1994)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 32 (1994), S. 199-204 
    Details
    ISSN: 0749-1581
    Keywords: NMR ; 13C NMR ; Conformation ; Ab initio calculations ; 1-cis-Methoxy-1,3-trans-butadiene ; 1-trans-Methoxy-1,3-trans-butadiene ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The proton-coupled 13C NMR spectra of 1-trans-methoxy- (2) and 1-cis-methoxy-1,3-trans-butadiene (3) are consistent with a methoxy heavy atom planar conformation with s-syn and s-anti orientations, respectively. Ab initio 6-31G* calculations confirmed such conformations. They were taken as model compounds to determine the influence of electrostatic interactions on the methoxy 13C NMR parameters. A shielding increase of 4 ppm is observed in 2, with respect to 3, for the OMe 13C chemical shift in an s-syn conformation and is ascribed to the attraction between the methyl and vinyl moieties as proposed by Li and Chesnut. The methyl 1J(C,H) coupling is not affected by this interaction, showing that the carbon 2p electrons are more polarizable than those in the 2s orbital.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260320402
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    Paper (German National Licenses)
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