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  • 1
    Electronic Resource
    Electronic Resource
    Substitutent effects in monosubstituted benzenes: Semi-empirical SCF studies of the Hammett constants (1995)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 8 (1995), S. 629-636 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Semi-empirical SCF calculations using the AM1 Hamiltonian were shown to account for the Hammett σ constants and other properties of a representative series of 22 monosubstituted benzenes in terms of the atomic charges at the ipso, ortho, meta and para positions. The trends of the correlations with experimental σ constants were found to follow the normal expectations of physical organic chemistry. Additional support for the AM1 charge distributions was obtained in correlations with the 13C chemical shifts of 12 of the test molecules. On the other hand, no correlations were found between σ constants and computed force constants for bending peripheral H atoms out of the plane of the aromatic ring, supporting the view that Hammett σ constants reffect charge distributions and not secondary effects expressed in the stiffness of bonds.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610081002
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  • 2
    Electronic Resource
    Electronic Resource
    Computational studies of peripheral ring twisting in meso-N-methyl pyridyl-substituted porphyrins (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 46 (1993), S. 701-709 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Semiempirical molecular orbital calculations for the porphyrins tetrakis(4-N-methyl pyridyl)porphine (H2TMpyP-4) and tetrakis(2-N-methyl pyridyl)porphine using the MNDO and AM-1 Hamiltonians suggest that twisting one or more of the pyridinium rings results, at considerable energy expense, in highly nonplanar macrocycle configurations as the exocyclic ring(s) approach coplanarity. The results imply that the mechanism of intercalation of H2TMpyP-4 into DNA cannot require twisting the exocyclic rings anywhere close to coplanarity with the central porphine core, but involves, instead, the inherent flexibility of DNA itself. © 1993 John Wiley & Sons, Inc.
    Additional Material: 10 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560460604
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    Paper (German National Licenses)
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