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  • 1
    Electronic Resource
    Electronic Resource
    Molecular reorientation from NMR relaxation times in planar molecules (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 58-69 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The spectral density J(0) for the autocorrelation function referred to an arbitrarily chosen body-fixed coordinate system has been rederived for a planar asymmetric rotor undergoing rotational diffusive motions. The angular dependence of J(0) was found to be more complicated than in the case of coincidence of the body-fixed frame with the principal axes of rotation. Therefore, the orientation of the principal axes of the rotational diffusion tensor can be determined from four different J(0) or 1/T1 values. This result disagrees with previous conclusions based upon the assumption that the same angular dependence should be expected irrespective of the relative orientation of the diffusion tensor axes. Likewise, the values of the three diffusion coefficients can be in principle determined from more than two (or three) different J(0) values for molecules with (or without) a binary symmetry axis. In practice, however, only two relations between them can usually be obtained due to the uncertainty in T1 measurements and to the relative insensitivity of J(0) to some correlated changes in the diffusion coefficients for moderate anisotropic molecular rotations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449793
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  • 2
    Electronic Resource
    Electronic Resource
    Relationships between Torsional Angles and Ring-Puckering Coordinates. 5. Application to Six-Membered Rings (1994)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 98 (1994), S. 10440-10446 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100092a010
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    ASIS effect for tetrahydroselenophene (1979)
    s.l. : American Chemical Society
    The @journal of organic chemistry 44 (1979), S. 3425-3426 
    Details
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/jo01333a038
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    Paper (German National Licenses)
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  • 4
    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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  • 5
    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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  • 6
    Electronic Resource
    Electronic Resource
    Methyl carbon chemical shifts of methylbenzoic acids and methylbenzoate anions (1984)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 22 (1984), S. 140-145 
    Details
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Methyl carbon chemical shifts have been assigned for methylbenzoic acids dissolved in CDCl3, and for methylbenzoate anions obtained by dissolving these acids in aqueous NaOH solution. Chemical shifts have been interpreted by means of additive substituent parameters which reflect conformational features existing between adjacent substituents. Barriers to rotation of a methyl group adjacent to a carboxyl or carboxylate group have been estimated to differ by less than 2 kJ mol-1 from the barrier of a methyl group in o-xylene.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1270220304
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  • 7
    Electronic Resource
    Electronic Resource
    Aryl carbon chemical shifts of methylbenzoic acids and methylbenzoate anions (1985)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 23 (1985), S. 442-449 
    Details
    ISSN: 0749-1581
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The aryl carbon chemical shifts of methylbenzoic acids in CDCl3 and methylbenzoate anions in aqueous NaOH solutions have been assigned. The shifts have been interpreted by means of a model based on the additivity of substituents which is similar to that previously developed for the analysis of the methyl chemical shifts. Corrective parameters included to take into account the interactions of adjacent substituents are found to be related to both the twist angle, θ, of the carboxyl or carboxylate substituents and the conformation of the methyl groups. The derived values of the twist angle are in closer agreement with x-ray data than those estimated from UV spectra or from Cl-PPP computations.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260230608
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  • 8
    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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