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  • 1
    Electronic Resource
    Electronic Resource
    Restricted rotation about partial C,N double bonds (1997)
    Springer
    Structural chemistry 8 (1997), S. 217-226 
    Details
    ISSN: 1572-9001
    Keywords: NMR ; ab initio calculation ; restricted rotation ; solvent effects ; NBO
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The restricted rotation about the partial C,N double bond in 2-chloro-6-NR2-pyran-4-ones is discussed in the light of NMR spectroscopic data and theoretical calculations.Ab initio calculations at the HF/6-31G* level were carried out using a continuum model to take solvent effects into account. The delocalization ofπ-electron density [described by natural bond orbital analysis (NBO)] was applied to determine the degree of conjugation in the ground state (GS) and in the transition state (TS) for the restricted rotation of the compounds studied. The reason for the different barriers to rotation of the NR2 substituents (pyrrolidino 〉 dimethylamino 〉 morpholidino 〉 piperidino) at the 2-chloro-pyran-4-one ring appears to be the different steric hindrance of the NR2 substituents in the GS for the restricted rotation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02263510
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  • 2
    Electronic Resource
    Electronic Resource
    Acyclic stereochemical analysis by NMR spectroscopy (1987)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 25 (1987), S. 990-995 
    Details
    ISSN: 0749-1581
    Keywords: NMR ; γ-chloropropyl methyl ethers ; Vicinal H,H coupling constants ; Steric compression Conformation ; Diastereomer assignment ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The diastereomers of a series of substituted γ-chloropropyl methyl ethers with up to three chiral centres have been assigned by 1H/13C NMR spectroscopy from vicinal H,H coupling constants and the steric compression within the carbon skeleton (γ-gauche effect). The necessary conformational study was carried out with the help of theoretically estimated steric 1,3-parallel interaction energies.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260251114
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  • 3
    Electronic Resource
    Electronic Resource
    Stereochemistry of crown ethers. V.For Part 4, see S. Stoss, E. Kleinpeter and H.-J. Holdt, Magn. Reson. Chem. 29, 999 (1991). - solution structure and complexational behaviour of dibenzo crown ethers (1992)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 30 (1992), S. 425-433 
    Details
    ISSN: 0749-1581
    Keywords: Dibenzo crown ethers ; Conformations ; NMR ; Molecular mechanics ; Alkali complexes ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preferred conformations and the complexing behaviour of 16- and 17-membered dibenzo crown ethers were studied by means of both NMR spectroscopy and molecular mechanical calculations. Conclusions could be drawn about the stoichiometry and stability of the alkali metal ion corand complexes. The spin-lattice relaxation times of the crown ether carbon atoms and the relevant complexes are discussed with respect to the intramolecular flexibility of these species. The intramolecular reorientations detected are reduced considerably in the alkali metal ion complexes. In the preferred conformers of corands 2, 3 and 6, the molecular mechanical calculations prove that the phenyl rings are positioned in a chair conformation at a twist to each other. The same phenyl rings in the crown ethers 1, 4 and 5 are in a boat conformation. These conformations seem to be important for the optimum complexation of the alkali cations.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260300514
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