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  • 1
    Electronic Resource
    Electronic Resource
    Nuclear Magnetic Shielding of Protons in Amides and the Magnetic Anisotropy of the C—O Bond (1959)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 63 (1959), S. 1388-1394 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j150579a012
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  • 2
    Electronic Resource
    Electronic Resource
    High Resolution Proton Magnetic Resonance Spectrum of Mercury Diethyl: Analysis of an A3B2 System (1960)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 82 (1960), S. 34-40 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja01486a009
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  • 3
    Electronic Resource
    Electronic Resource
    Proton Magnetic Resonance Spectra of Some Ethyl Compounds (1960)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 82 (1960), S. 5983-5986 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja01508a005
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  • 4
    Electronic Resource
    Electronic Resource
    Unrestricted Hartree-Fock spin density distributions in nitro aromatic radical anions (1971)
    Springer
    Theoretical chemistry accounts 22 (1971), S. 369-377 
    Details
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die Spindichteverteilungen in den Radikalanionen des Nitrobenzols und einiger parasubstituierter Nitrobenzole werden mit Hilfe des UHF-Formalismus von Amos und Snyder berechnet. Zur Ermittlung der Spindichte der nitroaromatischen Radikalanionen wird ein Parameterschema benutzt, das zufriedenstellende Darstellung der Elektronenübergänge und der molekularen Ionisationspotentiale von substituierten Benzolen (Nitrobenzol, Toluol, Anilin, Benzaldehyd, Benzonitril) gestattet. Der Einfluß der Spins von benachbarten Atomen auf die Hyperfeinaufspaltung des Stickstoffatoms wird diskutiert. Es zeigt sich, daß zur näherungsweisen Beschreibung des Stickstoffs der Nitrogruppe eine einfache Gleichung des McCornell-Typs ausreicht, wenn auch die Karplus-Fraenkel-Theorie eine bessere Abschätzung der14N-Aufspaltungskonstanten ermöglicht. Die σ-π-Parameter, die zur Voraussage der Stickstoff-Hyperfeinkopplung in Nitro-, Amino- und Cyanogruppen mit Hilfe der UHF-Spindichten erforderlich sind, werden zusammengestellt.
    Notes: Abstract The spin density distributions in the radical anions of nitrobenzene and some para substituted nitrobenzenes are calculated using the unrestricted Hatree-Fock formalism of Amos and Snyder. A parameter scheme which gives satisfactory account of the electronic transitions and molecular ionisation potentials of substituted benzenes (nitrobenzene, toluene, aniline, benzaldehyde and benzonitrile) is used for spin density calculations of the nitro radical anions. The importance of spin densities on neighbouring atoms on the hyperfine splitting of nitrogen atom is discussed. It is seen that although Karplus-Fraenkel theory gives a better estimate of14N splitting constant, the simple McConnell-type of relation is approximately valid for the nitro group-nitrogen. Theσ-π-parameters for use with unrestricted Hartree-Fock spin densities for the prediction of nitrogen hyperfine couplings in nitro, amino and cyano groups are summarised.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01036040
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  • 5
    Electronic Resource
    Electronic Resource
    Unrestricted hartree-fock calculation of spin distributions in some radical anions exhibiting restricted rotation about a carbon carbon bond (1967)
    Springer
    Theoretical chemistry accounts 8 (1967), S. 306-311 
    Details
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Bei früheren ESR-Untersuchungen an trans-Stilben, trans-Dipyridyläthylen, Terephthalaldehyd und Benzaldehyd wurde gefunden, daß sowohl die ortho- wie die meta-ständigen Ringprotonen nicht gleichwertig sind. Wir haben die Spindichten in diesen Systemen mit der UHF- und der UHFAA-Methode untersucht. Befriedigende Übereinstimmung mit experimentellen Ergebnissen wurde erzielt, ohne daß dazu der sogenante α- oder β-Effekt herangezogen werden mußte.
    Abstract: Résumé Dans les anions radicalaires du trans-stilbène, du trans-l,2-bis(4-pyridyl)-éthylène, des aldéhydes térephtaliques cis et trans, et de l'aldéhyde benzo'que, des expériences de r.p.e avaient montré que les deux protons en méta n'étaient pas équivalents. Nous avons effectué une étude systématique des distributions de spin dans ces systèmes en utilisant les méthodes U.H.F. (Hartree-Fock sans restriction) et U.H.F.A.A. (U.H.F. comportant l'annihilation de la composante quartet de spin). On a obtenu un accord satisfaisant avec les résultats expérimentaux dans le cadre de ces théories sans faire appel à de soi-disants effects α ou β.
    Notes: Abstract In the radical anions of trans-stilbene, trans-1,2-bis(4-pyridyl)-ethylene, cis and transterephthalaldehyde and benzaldehyde it has been found earlier by ESR experiments that the two ortho protons, as well as the two meta protons of the six-membered ring are not equivalent. We have made a systematic study of spin distributions in these systems by employing the UHF (Unrestricted Hartree Fock) and UHFAA (UHF incorporating the annihilation of the quartet spin component) methods. Satisfactory agreement with the experimental results has been obtained within the framework of these theories and without invoking the so called “α effect” or “β effect”.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00528175
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  • 6
    Electronic Resource
    Electronic Resource
    Study of the transition state in the isomerization of trans-N2F2 to cis-N2F2 by extended Hückel theory (1968)
    Springer
    Theoretical chemistry accounts 9 (1968), S. 268-274 
    Details
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Conclusion The quantitative agreement with experimental barrier height and the extra stabilization energy of cis-N2F2 over trans-N2F2 may not be considered to be very good, but this is only to be expected as small differences between large quantities are being calculated. It appears from our present calculations that the use of Cusachs relation for evaluating the off-diagonal matrix elements in this system is open to question since the experimentally observed planarity of N2F2 is not correctly predicted by the use of this relation. We therefore prefer the use of the Wolfsberg-Helmholz relation in this system. A value of K= 1.75 appears to be preferable. The results of all the E.H.T. calculations made here for difluorodiazine clearly show that a twisted transition state is more probable than a linear one (LT or LC) in the isomerization of trans-N2F2 to cis-N2F2. This conclusion also receives further support from a consideration of the high preexponential factor in the rate equation [1] and the multiplicity of the transition state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00526606
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  • 7
    Electronic Resource
    Electronic Resource
    Unrestricted Hartree-Fuck calculations of spin density distributions in the radical anions of some heterocycles derived from thiophene, furan and pyrrole (1968)
    Springer
    Theoretical chemistry accounts 11 (1968), S. 156-158 
    Details
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Spin density distributions in the radial anions of some heterocycles derived from thiophene, furan and pyrrole have been obtained using the unrestricted Hartree-Fock method. Good agreement between the calculated results and experimental data has been observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01184322
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  • 8
    Electronic Resource
    Electronic Resource
    Unrestricted Hartree-Fock spin density calculations with orthogonalized atomic orbitals on aza and nitroaromatic radical anions (1974)
    Springer
    Theoretical chemistry accounts 32 (1974), S. 321-330 
    Details
    ISSN: 1432-2234
    Keywords: Spin density ; Aza and nitroaromatic radical anions ; Proton and nitrogen hyperfine splittings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The spin density distributions in some aza and nitroaromatic radical anions have been calculated using Löwdin's orthogonalized basis set of atomic orbitals in the Unrestricted Hartree-Fock method of Amos and Snyder. The present calculations lead to a satisfactory account of proton splittings in these radicals. Least squares analyses correlating the observed 14N splittings and the spin density results over completely localized nonorthogonal basis have been separately carried out for aza and nitroaromatic radical anions and the sigma-pi parameters thus obtained are discussed and compared with earlier estimates for these quantities. Unlike the earlier results, the present estimate of Q NN N for aza and nitroaromatic radicals are not very much different from each other.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00526867
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  • 9
    Electronic Resource
    Electronic Resource
    Molecular orbital study of some heterocycles containing nitrogen and sulphur (1966)
    Springer
    Theoretical chemistry accounts 5 (1966), S. 401-405 
    Details
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Es wurde eine systematische HMO-Studie von 1, 2, 5-Thiadiazol (I), 2, 1, 3-Benzothiadiazol (II) und dem kürzlich synthetisierten Naphto-[2, 3-c]-1, 2, 5-thiadiazol (III) durchgeführt. Die HMO -Berechnung der Stabilität und Reaktivität ist in Übereinstimmung mit den experimentellen Ergebnissen. Theoretische Bindungslängen für (I) und (II) und Spindichten für (II) sind ebenfalls in Übereinstimmung mit den Experimenten, Bindungslängen und Spindichten für (III) werden vorausgesagt.
    Abstract: Résumé Utilisant la méthode des orbitales moléculaires de Hückel (HMO) nous avons étudié systématiquement les 1, 2, 5-thiadiazole (I), 2, 1, 3-benzothiadiazole (II) et le naphto [2, 3-c] 1, 2, 5 thiadiazole (III) récemment synthétisé. La stabilité et la réactivité de ces molécules, telles que la théorie les prédit, sont en bon accord avec les données expérimentales. Les longueurs des liaisons de (I) et (II) sont connues et sont en bon accord avec la théorie. Les densités de spin calculées pour l'anion radicalaire de (II) sont en bon accord avec l'expérience. On prédit les longueurs de liaison et la réactivité de (III) ainsi que les densités de spin de son anion radicalaire.
    Notes: Abstract A systematic study of 1, 2, 5-Thiadiazole (I), 2, 1, 3-Benzothiadiazole (II) and the recently synthesised Naphtho[2, 3-c]-1, 2, 5 thiadiazole (III) has been made using the Hückel molecular orbital theory (HMO). Stability and reactivity of these molecules as predicted by HMO calculations are in agreement with experimental observations. For (I) and (II) bond lengths are known and excellent agreement with theory has been shown. Spin densities calculated for the radical anion of (II) are in good agreement with experimental data. Bond lengths in (III) and its reactivity as well as the spin densities for its radical anion are predicted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00527042
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  • 10
    Electronic Resource
    Electronic Resource
    Approximate valence-shell electron unrestricted Hartree-Fock calculations with orthogonalized atomic orbitals: Proton hyperfine splittings in benzyl and related radicalsPaper presented at the First International Congress of Quantum Chemistry, Menton, France, July 4-10, 1973. (1974)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 8 (1974), S. 451-465 
    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 modified INDO procedure has been used to calculate the proton hyperfine splittings in benzyl and the isoelectronic anilino, phenoxy and 2-azabenzyl as well as 2- and 3-thenyl radicals. The present procedure differentiates between s-, p- and d-orbitals on an atom in estimating various integrals involving them, satisfies the rotational invariance requirements and employs an orthogonalized basis set of atomic orbitals for obtaining core-Hamiltonian matrix elements. The calculations based on using the exponents which depend only on the type of orbital and the nature of atom fail to provide correct relative order of ortho and para proton splittings in benzyl as well as anilino, phenoxy and 2-azabenzyl radicals. On the other hand, use of the exponents which are modified according to the charge densities in various orbitals leads to a high absolute value for para proton splitting compared to that for ortho proton splitting which in case of all these radicals is in agreement with experiment. A spin density calculation on benzyl, anilino and phenoxy radicals considering the variation of one-center one-electron and one-center two-electron integrals for different protons with their charges is found to yield further improvement in the relative order of ortho and para proton splittings in all these radicals. In 2- and 3-thenyl radicals the role of 3d-orbitals on sulfur has also been examined. To our knowledge, no unrestricted INDO calculations including 3d-orbitals on sulfur have been reported in the literature so far.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560080311
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