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  • 1
    Electronic Resource
    Electronic Resource
    NMR-Spektren einiger Benzylidenbarbitursäurederivate (1976)
    Springer
    Monatshefte für Chemie 107 (1976), S. 1115-1125 
    Details
    ISSN: 1434-4475
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The NMR-Spectra of substituted benzylidene barbituric acids, benzylidene dimethylbarbituric acids and some 1,4-and 1,3-cycloaddition products are reported. The signals of the olefinic protons and the N−CH3-signals depend on the conformation of the compounds. The NMR-Spectra of the anions are also given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00903798
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  • 2
    Electronic Resource
    Electronic Resource
    Elektronenlokalisierung im Grundzustand und in angeregten Zuständen Pars-Orbital-Methode, 12. Mitt (1979)
    Springer
    Monatshefte für Chemie 110 (1979), S. 505-515 
    Details
    ISSN: 1434-4475
    Keywords: Character orders ; Electron localization in excited states ; Electron localization in ground states ; Pars orbital method ; Significance index for pattern of fragmentations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract UsingGleason's theorem the pars orbital concept is developed for excited states of conjugated systems described by CI-methods. A significance index is introduced to evaluate different patterns of fragmentation. The usefulness of this approach is illustrated for butadiene, biphenyl, naphthalene, and azulene.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00938355
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  • 3
    Electronic Resource
    Electronic Resource
    1,4-Photoaddition of maleic anhydride to chrysene (1981)
    Springer
    Monatshefte für Chemie 112 (1981), S. 659-667 
    Details
    ISSN: 1434-4475
    Keywords: Chrysene ; Maleic anhydride ; Mechanism of photoaddition ; 1,4-Photoaddition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die Photo-Diels-Alder-Reaktion von Maleinsäureanhydrid mit Chrysen ergibt Chryseno[4,5-efg]-isobenzofuran-4,6-dion (VI). Schweratomexperimente mit Xenon als äußerer Störer zeigen, daß die Reaktion vom niedrigst angeregten Singulettzustand des Chrysens ausgeht. Die Abstraktion von Wasserstoffatomen aus dem primärenDiels-Alder-Addukt IV durch das Lösungsmittel CH2Cl2 folgt möglicherweise einem Zweistufenmechanismus. Die Reaktion stellt einen neuen Typ von Photoreaktion dar; möglicherweise folgt sie einem Mechanismus, der in der Photochemie neuartig ist.
    Notes: Abstract The photoDiels-Alder reaction of maleic anhydride with chrysene yields chryseno[4,5-efg]isobenzofuran-4,6-dion (VI). Heavy atom experiments using xenon as an external perturber show that the reaction occurs via the lowest singlet excited state of chrysene. Hydrogen is abstracted from the primaryDiels-Alder adduct IV by the solvent CH2Cl2 possibly in a two-step mechanism. The reaction presents a new type of photoreaction, its mechanism possibly follows a scheme not considered so far in photochemistry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00899679
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  • 4
    Electronic Resource
    Electronic Resource
    Molekulare Topologie (1984)
    Springer
    Naturwissenschaften 71 (1984), S. 623-629 
    Details
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00377896
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  • 5
    Electronic Resource
    Electronic Resource
    Elektronenstruktur und Spektren von Phenylcycloheptatrienylium-Kationen (1969)
    Springer
    Monatshefte für Chemie 100 (1969), S. 1-27 
    Details
    ISSN: 1434-4475
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Abstract The electron structures of phenylcycloheptatrienylium cations have been studied using one-electron LCAO-MO-methods (HMO- and EHM-method) and strong σ−π-interaction was observed between twisted rings. The calculated results were compared with UV and NMR spectra of 15 cations synthesized in part for the first time. The NMR spectra of phenylcycloheptatrienylium cations with and without substituents in positions 1 and 1′ were found to differ significantly. The differences can be accounted for assuming differently charged hydrogen atoms. A dihedral angle of ω〈45° probably can be assumed for cations without substituents in positions 1 or 1′.
    Notes: Zusammenfassung Die Elektronenstruktur von Phenylcycloheptatrienylium-Kationen wurde mit Hilfe von Einelektronen-LCAO-MO-Methoden (HMO- und EHM-Methode) untersucht. In den verdrehten Strukturen der Kationen tritt starke σ−π-Wechselwirkung von einem Ring zum anderen hin auf. Die Rechenresultate werden mit den UV- und NMR-Spektren von 15 zum Teil neu dargestellten Kationen verglichen. Die NMR-Spektren von Phenylcycloheptatrienyliumionen mit und ohne Substituenten in den Stellungen 1 oder 1′ unterscheiden sich signifikant voneinander. Diese Unterschiede können durch die verschiedenen Ladungsdichten an den einzelnen Wasserstoffatomen erklärt werden. Für die Kationen ohne Substituenten in den Stellungen 1 oder 1′ wird ein dihedraler Winkel ω〈45° wahrscheinlich gemacht.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00938231
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  • 6
    Electronic Resource
    Electronic Resource
    Über den Zusammenhang von Bindungslängen und Elektronegativitäten (1963)
    Springer
    Theoretical chemistry accounts 1 (1963), S. 308-315 
    Details
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Abstract The empirical equation (3) of Schomaker and Stevenson [7] for the relation between bond lengths and electronegativities is explained by means of quantum mechanics using a VB-function. The ionic and covalent bond energies respectively are approximated by adequate potential functions. For the ionic character of the bond a new term is derived containing the electronegativities; this term is tested using the dipole moments of diatomic molecules. Statistical investigations lead to values for the empirical constants of Schomaker and Stevenson [7] and Gordy [2], which agree well with the empirical values.
    Abstract: Résumé La formule empirique (3) présentée par Schomaker et Stevenson [7] pour la correlation entre les longueurs des liaisons et les électronégativités est expliquée à l'aide d'une fonction VB ondulatoire. Les potentiels des valences ioniques et covalentes sont approximés et une formule nouvelle pour le degré d'ionicité de la liaison contenant les électronégativités est dérivée. Cette formule est examinée pour les moments dipolaires des atomes diatomiques. Un procédé statistique donne des valeurs en bon accord avec les constantes empiriques données par Shomaker et Stevenson [7] et par Gordy [2].
    Notes: Zusammenfassung Die von Schomaker und Stevenson [7] aufgestellte empirische Formel (3) für den Zusammenhang von Bindungslängen und Elektronegativitäten wird quantenchemisch mit Hilfe einer VB-Funktion begründet. Hierbei werden die ionischen bzw. kovalenten Bindungsenergien durch entsprechende Potentialfunktionen angenähert und für den ionischen Charakter der Bindung ein neuer, aus den Elektronegativitäten aufgebauter Ausdruck abgeleitet, dessen Güte an den Dipolmomenten zweiatomiger Moleküle überprüft wird. Auf Grund einer statistischen Betrachtung ergeben sich für die von Schomaker und Stevenson [7] bzw. von Gordy [2] angegebenen empirischen Konstanten Zahlenwerte, welche mit den empirischen Größen gut übereinstimmen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00528762
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  • 7
    Electronic Resource
    Electronic Resource
    Über den Zusammenhang von Kovalenzradien und Elektronegativitäten (1963)
    Springer
    Theoretical chemistry accounts 1 (1963), S. 316-326 
    Details
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Abstract For the calculation of the covalent radii a new empirical function (2) is given containing the electronegativities and a parameter (called shell constant here), which depends only on the principal quantum number of the valence electrons. This parameter is simply related to the charge cloud density of the Slater atomic orbitals on the one hand and on the other hand to the bond force constants b ij of Badger'S [3] empirical function (6). Furthermore a new system of covalent radii is calculated taking as basis the function (1) of Schomaker and Stevenson [10] and using the method of least squares.
    Abstract: Résumé Une nouvelle formule empirique (2) est donnée pour le calcul des rayons covalents, contenant les électronégativités et un paramètre (nommé constante de couche) qui ne dépend que du nombre quantique principal des électrons de valence. Cette constante de couche est liée à la distribution de la densité électronique dans les orbitales atomiques de Slater, et aussi aux b ij de la formule empirique (6) de Badger [3] pour les constantes de force. En outre, un système nouveau de rayons oovalents suivant l'équation (1) de Schomaker et Stevenson [10] est calculé par la méthode des moindres carrés.
    Notes: Zusammenfassung Zur Berechnung der Kovalenzradien wird eine neue empirische Formel (2) aufgestellt, in welche die Elektronegativitäten und ein nur von der Hauptquantenzahl der Valenzelektronen abhängiger Parameter, den wir Schalenkonstante genannt haben, eingehen. Diese Schalenkonstanten hängen einerseits mit den Elektronendichteverteilungen der Slater-Atom-Orbitale und andrerseits mit den Konstanten b ij der von Badger [3] gefundenen empirischen Formel (6) für die Kraftkonstanten einfach zusammen. Ferner wird unter Zugrundelegung der Gl. (1) von Schomaker und Stevenson [10] nach der Methode der kleinsten Quadrate ein neues System von Kovalenzradien berechnet.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00528763
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  • 8
    Electronic Resource
    Electronic Resource
    SCF perturbation theory for unimolecular reactions (1979)
    Springer
    Theoretical chemistry accounts 50 (1979), S. 327-342 
    Details
    ISSN: 1432-2234
    Keywords: Unimolecular reactions ; potential energy surfaces of ∼ ; SCF perturbation theory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A CNDO/2 SCF perturbation theory is presented for interpreting the form of CNDO/2 potential energy surfaces of unimolecular reactions. The analysis is performed by calculating the energy change Δ E arising from a distortion of the molecular geometry along the reaction coordinate. Δ E is decomposed into different perturbational contributions which are appropriate for an interpretation of the perturbation energy Δ E. Moreover, Δ E is resolved into energy parts arising from a single occupied orbital and contributions due to pairwise orbital interactions. In this way one evaluates numerically how the form of the occupied and unoccupied orbitals determines the magnitude of Δ E. If the distortion occurs along a definite symmetry coordinate, group-theoretical arguments can be applied to discuss the magnitude of characteristic components of the perturbation energy. The SCF perturbation theory is used to analyze the isomerization of ethylene, cis-2-butene and cis-2-butenenitrile.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00551340
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  • 9
    Electronic Resource
    Electronic Resource
    The effect of molecular topology on π-molecular-orbital energies (1985)
    Springer
    Theoretical chemistry accounts 67 (1985), S. 63-89 
    Details
    ISSN: 1432-2234
    Keywords: Topological-effect-on-molecular-orbitals (TEMO) theorem ; non-empirical HF SCF calculations ; perturbational-variational Rayleigh-Ritz (PV-RR) analysis ; topological molecular models
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Three models for constructing topologically related pairs of molecular isomers are discussed at length. The topological-effect-on-molecular-orbitals (TEMO) theorem is presented in detail and illustrated with experimental data; this theorem demonstrates that molecular topology imposes constraints in the form of general interlacing rules on the MO energy patterns of topologically related molecules. Further, non-empirical SCF MO calculations have been performed for topologically related o- and p-divinylbenzenes, difluorobenzenes, benzoquinones, and benzoquinodimethanes in standard and optimized geometries using various basis sets. In most cases, the SCF π-MO eigenvalue patterns of topological related isomers are in complete agreement with the TEMO theorem, thus demonstrating the dominant influence of topology on the π-MO energies. A modified version of the generalized perturbationalvariational Rayleigh-Ritz (PV-RR) procedure is described which is used to study the occasional observed deviations from the TEMO predictions; this procedure had been combined with the concept of critical λ (i.e. the threshold value of the perturbation parameter λ at which the TEMO order of a pair of MO eigenvalues starts to invert), thus enabling us to analyze in quantitative detail the physical factors which compete with molecular topology in conditioning the ab initio MO energy patterns.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00547896
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  • 10
    Electronic Resource
    Electronic Resource
    Structure and properties of non-classical polymers II. Band structure and spin densities (1985)
    Springer
    Theoretical chemistry accounts 67 (1985), S. 211-228 
    Details
    ISSN: 1432-2234
    Keywords: Nonclassical polymers ; band structure of ∼ ; cassification and spin densities of ∼
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Theoretical investigation of the band structure of three types of nonclassical polymers, namely alternant (one- and two-dimensional), nonalternant and heteroatomic, are carried out. Although polyradicals, these polymers have a considerable delocalization energy which may determine their relative stability. The spin-density distribution of the alternant type of non-classical polymers corresponds to a ferrimagnetic ground state at 0 K. The non-classical polymers represent a new class of organic systems as their band structure and magnetic properties essentially differ from those of common polymers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00551267
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