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  • 1985-1989  (224)
  • 1935-1939
  • 1850-1859
  • Computational Chemistry and Molecular Modeling  (224)
  • 1
    Electronic Resource
    Electronic Resource
    Spectroscopic studies on some phenylethylamine drugs: Molecular orbital calculations (1987)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 855-869 
    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: The electronic absorption spectra of some phenylethylamine drugs, namely, d-pseudoepherine, l-pseudoephedrine, l-ephedrine, dl-ephedrine dl-norephedrine, phenylethylamine, methoxyphenamine, and l-noradrenaline were investigated in polar and nonpolar solvents. The observed transitions were interpreted, and the role of σ-π interaction was explored. Molecular orbital calculations were performed on representatives of the above group of compounds, namely, d-pseudoephedrine, l-ephedrine, and l-noradrenaline using the INDO procedures and adopting the best conformer of the molecule. The transition energy, band intensity, and dipole moments were calculated and corresponded satisfactorily with the experimental values.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560310603
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  • 2
    Electronic Resource
    Electronic Resource
    The difluoroethylenes: A reconsideration of the “Cis effect” (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 61-72 
    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: Ab initio molecular orbital calculations have been carried out on all three isomers of difluoroethylene with geometry optimization. The calculations were done with a “double-zeta” basis set. After correction of the SCF energies for the effect of electron correlation, the 1,1-isomer is shown to be 8 kcal/mole lower in energy than the cis, which is 1 kcal/mole more stable than the trans. As the stabilization of the isomers increases, the distance between the fluorine atoms decreases: trans, 3.57 Å; cis, 2.77 Å; 1,1-isomer 2.20 Å. A simple explanation for these trends is based upon electrostatics and the small size and high electronegativity of the fluorine atom. As the fluorine atoms come closer together, the destabilization due to nuclear repulsions and electron repulsions is offset by the increased stabilizing electrons-nuclei attractions.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290107
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    On the use of perturbation theory corrections to numerically selected MRDCI calculations (1985)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 6 (1985), S. 88-92 
    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: If numerical configuration selection procedures are used in MRDCI calculations, the full MRDCI energy may be estimated by adding energy corrections obtained by perturbation theory. Accurate results may then be obtained by including all selected CFs in the zero-order function instead of only the reference CFs.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540060203
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Molecular mechanics (MM2) calculations on peptides and on the protein Crambin using the CYBER 205 (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 10 (1989), S. 503-513 
    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: The MM2 potential functions for amides and peptides have been further extended by examining the experimental crystal structures for cyclo-(-Ala-Ala-Gly-Gly-Ala-Gly-), I, and cyclo-(-Ala-Ala-Gly-Ala-Gly-Gly-), II. The force field obtained was then applied to a study of the structure of the hydrophobic protein Crambin, for which a high resolution crystal structure is available. The energy minimization was carried out using a version of MM2 adapted to the CYBER 205.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540100408
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Isoscalar factors for tetragonal, orthorhombic, monoclinic and triclinic shubnikov point groups (1985)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 27 (1985), S. 45-58 
    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: The relations between isoscalar factors for corepresentations of antiunitary magnetic point groups are discussed in the case of associated corepresentations. The tables of the isoscalar factors for the single- and double-valued corepresentations of all tetragonal, orthorhombic, monoclinic, and triclinic Shubnikov point groups are given. Some peculiarities of the calculation method of the isoscalar factors for corepresentations are considered.
    Additional Material: 10 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560270104
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  • 6
    Electronic Resource
    Electronic Resource
    Ab initio quantum-mechanical calculations on trifluoromethylamine (1985)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 28 (1985), S. 163-180 
    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: Extensive ab initio molecular-orbital calculations were carried out on trifluoromethylamine (TFM) to elucidate changes in geometry and electronic structure upon fluorination. The calculations show that the decomposition of CF3NH2 is slightly endoenergetic, and the heats of atomization of CF3NH2 and CH3NH2 show decreased stability of the species upon fluorination. Characteristic of CF3NH2 is a highly polar, strong, short CN bond. More limited calculations were carried out on CF3OH and CH3OH, and the electronic structure of CF3OH is found to be generally similar to that of CF3NH2. The reduced basicity of the fluorinated amine cannot be ascribed to the inductive effect; the enhanced acidity of the fluorinated alcohol reflects the weakening of the OH bond. No evidence leads to a confirmation of the existence of nitrogen-fluorine hyperconjugation in the fluorinated amine.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560280202
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    Atomic energy levels from configuration interaction calculations with relativistic corrections (1989)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 35 (1989), S. 325-330 
    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: It is shown that configuration interaction calculations, with inclusion of the relativistic corrections, constitute an appropriate approach for the prediction of atomic energy levels and that results of experimental accuracy are possible given the availability of large-scale, fast computers. The results obtained for He through F emphasize both the practical difficulties to be encountered and the possibility of predictions with less than 1% error.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560350209
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  • 8
    Electronic Resource
    Electronic Resource
    Numerical method for the open-shell restricted hartree-fock density-matrix direct calculation (1985)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 27 (1985), S. 653-664 
    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: A new computation procedure for direct calculation of the density matrix in the LCAO version of the restricted Hartree-Fock-Roothaan open-shell theory is analyzed. It is proved that the procedure is quadratically convergent and stable to the round-off errors independently of the Fock operator spectrum. The dependence of the limit matrix of the initial matrix is examined.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560270603
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  • 9
    Electronic Resource
    Electronic Resource
    An ab initio study of intermolecular hydrogen bonding between small peptide fragments (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1241-1251 
    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: Several small peptide fragments are investigated with ab initio (Hartree-Fock) calculations, using Gaussian basis sets. Complexation energies, net atomic charges, and optimum geometries are obtained. The geometries predicted by the STO-6G, and 6-31G* basis sets are quite similar, whereas the binding energies obtaiend by the 6-31G calculations are higher than those obtained with STO-6G and 6-31G* basis sets.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290521
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  • 10
    Electronic Resource
    Electronic Resource
    The use of inner projections of the polarization propagator to study different contributions to the magnetic shielding tensor. I. Proton deshielding by steric compressionPart of a PhD thesis (M.B.F.) to be presented to the University of Buenos Aires. (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 30 (1986), S. 77-88 
    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: A new method for studying different contributions to the magnetic shielding tensor is proposed. These contributions come from different molecular fragments, which are defined through a localization procedure. They are obtained by means of inner projections of the polarization propagator onto the subspace defined by the chosen molecular fragment. To illustrate the utility of this method, results are presented for the proton desheilding effect of steric crowding. Different degrees of approximation both in the polarization propagator formalism and in the ground state wave function can be used. Results presented in this paper were obtained at the INDO level, within the CHF scheme. Good agreement with experimental values is obtained.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560300108
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