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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Structural chemistry 3 (1992), S. 143-146 
    ISSN: 1572-9001
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 5
    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: Structural properties of cyclopropabenzene and its heteroanalogs are studied at the SCF 6-31G level of theory. It is found that the Mills-Nixon (MN) type of localization within the benzene ring is present in these systems. The origin of the bond fixation lies in rehybridization at the carbon junction atoms. π-electron bond orders usually follow changes within the sigma framework but can be misleading sometimes. It is shown that a judicious choice of heteroatoms can considerably enhance the MN effect. A refined and better definition of the MN effect is offered. Finally, present calculations and analysis of the results in terms of hybridization model and π-bond orders strongly indicate that experimental 4J(H—C—C—Me) proton-proton spin-spin couplings over four bonds can be used in identification of the MN effect only with extreme caution.
    Additional Material: 4 Tab.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 14 (1969), S. 396-401 
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die Elektronenstruktur von cis-1,2,3-Tricyanocyclopropan wurde mit der Methode der maximalen Überlappung und unter Verwendung von Clementi-Funktionen untersucht. Dabei wurde angenommen, daß die Bindungsenergien proportional zu den entsprechenden Überlappungsintegralen sind. Die entsprechenden Faktoren wurden an Äthylen, Vinylzyanid und Tetrazyanoäthylen getestet. Die Ergebnisse zeigen, daß die Bindungen im cis-1,2,3-Tricyanocyclopropanring gekrümmt sind. In diesem Zusammenhang wurde auch auf die Möglichkeit komplexer Hybride in gespannten Molekülen eingegangen. Es zeigt sich dabei, daß das Prinzip der maximalen Überlappung notwendig zu reellen Hybriden und damit zu gekrümmten Bindungen führt.
    Abstract: Résumé La structure électronique du cis-1,2,3, tricyanocyclopropane a été étudiée en utilisant la méthode du recouvrement maximum pour les orbitales atomiques de Clémenti. On suppose que les énergies de liaison sont proportionelles aux intégrales de recouvrement correspondantes. Les facteurs d'ajustement ont été testés sur l'éthylène, le cyanure de vinyle et le tétracyanoéthylène. L'existence de liaisons courbes dans le cycle du cis-1,2,3, tricyanocyclopropane est confirmée. On discute de la possibilité de l'hybridation complexe dans les molécules à tensions internes. Il est montré que le principe du recouvrement maximum conduit nécessairement à une hybridation réelle et par conséquent à des liaisons courbes.
    Notes: Abstract The electronic structure of cis-l,2,3-tricyanocyclopropane has been studied by the maximum overlap method, using Clementi atomic orbitals. It is assumed that the bond energies are proportional to the corresponding overlap integrals. Scale factors were checked on the ethylene, vinylcyanide and tetracyanoethylene. Bent bonds in the cis-1,2,3-tricyanocyclopropane ring are confirmed. The possibility of the complex hybridisation in strained molecules is discussed. It is shown that the principle of maximum overlap necessarily leads to real hybridisation and consequently to the bent bonds.
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  • 7
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Für einige dreißig Kohlenwasserstoffe wurde der mittels der Methode maximaler Überlappung berechnete s-Charakter mit den CH- und CC-Spinkopplungskonstanten in Zusammenhang gebracht. Dabei ergeben sich folgende Relationen: $$J_{{\text{C}}^{{\text{13}}} - {\text{H}}} = 1079a_{{\text{CH}}}^{\text{2}} /(1 + S_{{\text{CH}}}^{\text{2}} ) - 54,9,$$ $$J_{{\text{C}}_{\text{1}}^{{\text{13}}} - {\text{C}}_{\text{2}}^{{\text{13}}} } = 1020,5a_{{\text{C}}_{\text{1}} }^2 a_{{\text{C}}_{\text{2}} }^{\text{2}} /(1 + S_{{\text{CC}}}^{\text{2}} ) - 8,2.$$ (Kopplungskonstanten in cps-Einheiten !) Im einzelnen basiert die Berechnung des s-Charakters entweder auf der experimentellen oder einer Standard-Bindungslänge. Für die CH-Konstanten sind die Standardabweichungen 0,9 und für die entsprechenden CC-Werte 1,9 cps. Die große additive Konstante in der Korrelationsbeziehung der CH-Konstanten wurde auf den teilweisen ionischen Charakter der CH-Bindungen zurückgeführt. Die gute Übereinstimmung mit den experimentellen Daten weist darauf hin, daß der Fermi-Kontaktterm und die Hybridisierung tatsächlich die dominierenden Faktoren für die CH- und CC-Kopplungskonstanten einer Bindung, zumindest im Fall von Kohlenwasserstoffen, sind.
    Abstract: Résumé Le caractère s des hybrides à recouvrement maximum obtenus pour une trentaine d'hydrocarbures a été corrélé avec les constantes de couplage spin-spin C-H et C-C. Les relations suivantes ont été obtenues: $$J_{{\text{C}}^{{\text{13}}} - {\text{H}}} = 1079a_{{\text{CH}}}^{\text{2}} /(1 + S_{{\text{CH}}}^{\text{2}} ) - 54,9,$$ $$J_{{\text{C}}_{\text{1}}^{{\text{13}}} - {\text{C}}_{\text{2}}^{{\text{13}}} } = 1020,5a_{{\text{C}}_{\text{1}} }^2 a_{{\text{C}}_{\text{2}} }^{\text{2}} /(1 + S_{{\text{CC}}}^{\text{2}} ) - 8,2.$$ Les constantes de couplage sont experimées en unités cps. Dans le calcul des hybrides on a utilisé soit les longueurs de liaison expérimentales soit des longueurs de liaison standards. Les déviations standards pour les constantes de couplage $$J_{{\text{C}}^{{\text{13}}} - {\text{H}}}$$ et $$J_{{\text{C}}^{{\text{13}}} - {\text{H}}} $$ sont respectivement de 0,9 cps et 1,9 cps. Il a été suggéré que la grande constante additive présente dans $$J_{{\text{C}}^{{\text{13}}} - {\text{H}}}$$ Peut être attribuée au caractère ionique des liaisons CH. Le bon accord avec les données expérimentales affermit la conception selon laquelle le contact de Fermi et l'hybridation sont les facteurs dominants dans la détermination des constantes de couplage spin-spin CH et CC, du moins en ce qui concerne les hydrocarbures.
    Notes: Abstract For some thirty hydrocarbons the s character of hybrids obtained by the application of the maximum overlap method have been correlated with C-H and C-C spin-spin coupling constants. The following relationships were obtained: $$J_{{\text{C}}^{{\text{13}}} - {\text{H}}} = 1079a_{{\text{CH}}}^{\text{2}} /(1 + S_{{\text{CH}}}^{\text{2}} ) - 54.9$$ , $$J_{{\text{C}}_{\text{1}}^{{\text{13}}} - {\text{C}}_{\text{2}}^{{\text{13}}} } = 1020.5a_{{\text{C}}_{\text{1}} }^2 a_{{\text{C}}_{\text{2}} }^{\text{2}} /(1 + S_{{\text{CC}}}^{\text{2}} ) - 8.2$$ . Here the coupling constants are expressed in cps units. In the calculation of the maximum overlap hybrids either the experimental bond lengths or a standard bond lengths were used. For the $$J_{{\text{C}}^{{\text{13}}} - {\text{H}}}$$ and $$J_{{\text{C}}^{{\text{13}}} - {\text{H}}} $$ coupling constants the standard deviations are 0.9 cps and 1.9 cps respectively. It has been suggested that the large additive constant in the $$J_{{\text{C}}^{{\text{13}}} - {\text{H}}}$$ correlation may be attributed to the ionic character of C-H bonds. A good agreement with the experimental data strongly supports the idea that the Fermi contact term and the hybridization are dominant factors in determining carbon-hydrogen and carbon-carbon spin-spin coupling constants across one bond, at least in hydrocarbons.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 7 (1967), S. 253-255 
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Es wurde die Aufspaltung derd-Zustände für siebenkoordinierte Komplexe des NbF7 2− Typs mittels eines Punktladungsmodells berechnet. Die Störungsenergien werden als Funktion von λ =G 2/G 4 gegeben. Die Ergebnisse hängen empfindlich von den angenommenen Bindungswinkeln ab.
    Abstract: Résumé La séparation des orbitalesd dans les complexes à sept ligandes du type NbF7 2−est calculée d'après la méthode à charges ponctuelles. Les énergies de perturbation sont données en fonction de λ =G 2/G 4. Les résultats sont très sensibles envers les angles de valence adoptés.
    Notes: Abstract The splittings ofd-orbitals for seven coordinated complexes of the type NbF7 2− is calculated using a point charge model. The perturbed energies are expressed as a function of λ =G 2/G 4. The results are very sensitive on assumed geometrical angles of the molecule.
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  • 10
    ISSN: 1432-2234
    Keywords: Fused molecules ; Hybridization ; Localization of electrons ; Mills ; Nixon effect ; Rehybridization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Structural features of some naphthocyclobutenes and naphtho(b)cyclobutadiene are studied by semiempirical andab-initio procedures. It is found that Mills-Nixon (MN) effect is operative in all investigated molecules. Naphtho(b)cyclobutadiene exhibits the strongest MN type of deformation as anticipated. The calculated CC bond distances are in good accordance with available experimental data. They are rationalized by changes in hybridization parameters and π-bond orders. The rehybridization usually prevails in determining extent of the MN-deformation.
    Type of Medium: Electronic Resource
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