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  • 1
    Electronic Resource
    Electronic Resource
    Proton magnetic shielding in the water molecule (1972)
    Springer
    Theoretical chemistry accounts 27 (1972), S. 135-145 
    Details
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die ungekoppelte Hartree-Fock Variationsstörungsrechnung von Karplus u. Kolker wird für die Berechnung von Eigenschaften 2. Ordnung des Wassermoleküls verwendet. Für die Berechnung wird die SCF MO SCGO-Wellenfunktion des Grundzustandes gewählt, und die gestörten Orbitale 1. Ordnung werden in der multiplikativen Form approximiert. Die Konvergenz der Methode und die Frage, ob die Eichinvarianz verletzt wird, werden untersucht. Für den gewählten Potential-Nullpunkt im Zentrum der negativen Ladungsverteilung beträgt die errechnete Protonenabschirmungskonstante 28,30 ppm in guter Übereinstimmung mit den experimentellen Werten (30.20, 30.03 + 0.60 ppm). Die Ergebnisse für die magnetische Suszeptibilität des Wassermoleküls sind gleichfalls in vernünftiger Übereinstimmung mit dem Experiment.
    Notes: Abstract The variation-perturbation uncoupled Hartree-Fock procedure of Karplus and Kolker is employed for the calculation of the second-order properties of the water molecule. The SCF MO LCGO ground state wave function was chosen and the first-order perturbed orbitals were approximated in the multiplicative form. The convergence of the method as well as the violation of the gauge independence are studied. For the preferred gauge origin at the electronic centroid the calculated proton shielding constant is 28.30 ppm and compares favourably with the experimental data (30.20, 30.03 ±0.60 ppm). The results for the magnetic susceptibility of the water molecule are also in reasonable agreement with experimental values.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00528156
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  • 2
    Electronic Resource
    Electronic Resource
    Proton magnetic shielding in H2O and (H2O)2 (1973)
    Springer
    Theoretical chemistry accounts 30 (1973), S. 257-265 
    Details
    ISSN: 1432-2234
    Keywords: Proton magnetic shielding ; Hydrogen bond NMR shift of water molecule and dimer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The proton magnetic shielding constants in the water molecule and its linear perpendicular dimer are computed from SCF-MO-LCGO wave functions by using the uncoupled Hartree-Fock variation-perturbation procedure due to Karplus and Kolker. The convergence of the calculated shielding constants as well as their gauge dependence is studied. The final results for 17-term polynomial variation function indicate that the best choice for the gauge origin corresponds to the molecular electronic centroid. The calculated proton magnetic shielding constant in the water molecule is in remarkable agreement with experimental data and favourably compares with the best coupled Hartree-Fock results. It follows from the calculations for the water dimer that the H-bond NMR-shift amounts in this case —1.0 ppm and qualitatively agrees with the experimental data for the liquid water.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00527616
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  • 3
    Electronic Resource
    Electronic Resource
    Approximate variation-perturbation calculations of the second-order molecular properties (1971)
    Springer
    Theoretical chemistry accounts 21 (1971), S. 159-167 
    Details
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Das Variations-Störungsverfahren wird im Rahmen der CNDO/2-Näherung zur Berechnung von elektrischen Polarisierungstensoren zweiatomiger Moleküle herangezogen. Die Resultate ähneln denen des analogen, aber auf ab initio-Rechnungen basierenden Verfahrens mit einem minimalen Satz von Slaterfunktionen. Es ergibt sich, daß die Berechnung der Anisotropien nicht möglich ist, wohl aber die der räumlichen Mittelwerte.
    Notes: Abstract The variation-perturbation technique is applied to the calculation of the electric polarizability tensor of diatomic molecules within the CNDO/2 approximation. The results obtained in this paper are similar to those found in the non-empirical variation-perturbation approach within the minimal STO basis set. They are also compared with other CNDO/2 calculations and with existing experimental data. It follows from this comparison that the CNDO/2 variation-perturbation method does not allow for the calculation of the polarizability anisotropies. On the other hand, the rotational average of the polarizability tensor can be predicted in agreement with both the experimental data and nonempirical results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00530213
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  • 4
    Electronic Resource
    Electronic Resource
    CNDO calculations of diamagnetic shielding in molecules (1970)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 2 (1970), S. 63-69 
    Details
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An approximate procedure for the calculation of diamagnetic shielding in molecules is presented. The method proposed is based on the ‘complete neglect of differential overlap’ (CNDO) molecular wave functions and is formulated according to the zero differential overlap (ZDO) approximation. The results obtained with several CNDO-type wave functions for diatomic and polyatomic molecules are in very good agreement with non-empirical SCF calculations. The 14N diamagnetic shielding constants in several molecules were computed and some approximations usually adopted in the interpretation of 14N chemical shifts are critically discussed. It was shown that in some cases the observed 14N chemical shifts cannot be interpreted solely in terms of the paramagnetic contribution to the shielding constant.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1270020108
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  • 5
    Electronic Resource
    Electronic Resource
    14N chemical shifts in the enamino ketone quaternary ammonium salts (1971)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 3 (1971), S. 589-594 
    Details
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 14N chemical shifts were measured for a series of quaternary ammonium salts of enamino ketones. An upfield shift of the 14N resonance signals upon quaternization has been observed. The interpretation in terms of the approximate theory of nuclear magnetic shielding is given. The calculations for some model systems result in a general agreement with the experimental data.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1270030514
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    Paper (German National Licenses)
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