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  • 11
    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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  • 12
    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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  • 13
    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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  • 14
    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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  • 15
    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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  • 16
    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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  • 17
    Electronic Resource
    Electronic Resource
    Zur Clar'schen Theorie Lokaler Benzoider Gebiete in Kondensierten Aromaten (1967)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 1 (1967), S. 379-401 
    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
    Description / Table of Contents: By means of the HMO method a postulate by Clar is justified. According to this postulate certain localized benzene-like regions exist in condensed aromatic hydrocarbons. A measure of the benzene character, butene character, etc., of certain parts of these molecules is derived and a simple method to calculate it is described. The importance of these measurements for discussions of chemical reactivity is pointed out.
    Abstract: Mit Hilfe der HMO Methode wird gezeigt, dass das Postulat von E. Clar, gewisse Sechsring-Einheiten in kondensierten Aromaten stellen lokale benzoide Gebiete dar, berechtigt ist. Eine Masszahl (Character order) für den benzoiden, butenoiden usw. Charakter bestimmter Teile kondensierter Aromaten wird abgeleitet und ein einfaches Rechenverfahren zu ihrer Ermittlung angegeben. An Hand der Charakterogramme von 41 kondensierten Aromaten wird die Bedeutung dieser Zahlen für die Diskussion der chemischen Reaktivität aufgezeigt.
    Notes: Partant de la méthode HMO on vérifie qu'un postulate de Clar est justifié. D'après ce postulat il existe dans les hydrocarbures aromatiques condensés certaines régions localisées de caractère benzènoide. On propose un indice pour le caractère benzèneoide, butènoide, etc., de certaines parties de ces molécules, et on présente une méthode simple pour calculer ces indices. On discute l'importance de ces indices pour la réactivité chimique.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560010412
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  • 18
    Electronic Resource
    Electronic Resource
    Zur Kenntnis organischer Lewis-Säuren, 34. Die thermische [4π + 2π]-Cycloaddition von Enolethern an 1,1-dicarbonylsubstituierte Ethene (1980)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 113 (1980), S. 1020-1032 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Organic Lewis Acids, 341. Thermal [4π + 2π]-Cycloaddition of Enol Ethers to 1,1-Dicarbonyl Substituted EthenesEnol ethers such as ethyl vinyl ether and 1,1-dimethoxyethene (3f) react thermally, in some instances below 0°C, with cyclic 2-alkylidene-1,3-dicarbonyl compounds such as 1 and 2 to give [4π + 2π]-cycloadducts 4 and 5, respectively (cyclic enol acetals and enol orthoesters), and with 1,1-dicyanoethenes 6 to give [2π + 2π]-cycloadducts 7. On passing from toluene to acetonitrile as the solvent, rates of formation of 4bf from 1b and 3f increase about tenfold and those of 7b from 6b and 3f about sixfold. A discussion of these rates, including rates of related reactions, the relative Lewis acid strengths of 1b and 6b, and the behaviour of 1b/3f towards methanol leads to the conclusion that the degree of concert of the formation of 4bf is below 6.5 kJ · mol-1. - The configurations and conformations of adducts 4 and 5 are discussed.
    Notes: Enolether wie Ethylvinylether und 1,1-Dimethoxyethen (3f) bilden mit exocyclisch 1,1-dicarbonylsubstituierten Ethenen wie 1 und 2 z.T. schon unterhalb von 0°C thermisch die [4π + 2π]-Addukte 4 bzw. 5 (cyclische Enolacetale und Enolorthoester) und mit den 1,1-Dicyanethenen 6 die [2π + 2π]-Addukte 7. Die Bildungsgeschwindigkeit von 4bf aus 1b und 3f steigt auf etwa das Zehnfache und die von 7b aus 6b und 3f auf etwa das Sechsfache beim Übergang von Toluol auf Acetonitril als Lösungsmittel. Eine Diskussion dieser Bildungsgeschwindigkeiten unter Einbeziehung verwandter Reaktionsgeschwindigkeiten sowie der relativen Lewis-Säurestärken von 1b und 6b und des Verhaltens des Systems 1b/3f gegenüber Methanol führt zum Schluß, daß der energetische Konzertiertheitsgrad der Bildung von 4bf unter 6.5 kJ · mol-1 liegt. Die Konfigurationen und Konformationen der Addukte 4 und 5 werden diskutiert.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19801130321
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  • 19
    Electronic Resource
    Electronic Resource
    Synthesis and twisted intramolecular charge transfer(TICT)-fluorescence of 8,8′-bi-naphtho[1,2,3,4-def]chrysenyl (1986)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 119 (1986), S. 1683-1688 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Synthese und intramolekulare Charge-Transfer(TICT)-Fluoreszenz von 8,8π-Bi-naphtho[1,2,3,4-def]chrysenylBei der Belichtung von Naphtho[1,2,3,4-def]chrysen (3) in Chlorbenzol entsteht ein neues symmetrisches Biaryl, 8,8′-Bi-naphtho[1,2,3,4-def]chrysenyl (4). Fluoreszenzuntersuchungen an 4 ergaben, daß die Emission aus einem TICT-Zustand erfolgt.
    Notes: Upon irradiation of naphtho[1,2,3,4-def]chrysene (3) in chlorobenzene a symmetric biaryl, 8,8′-bi-naphtho[1,2,3,4-def]chrysenyl (4), is formed. Fluorescence studies of 4 reveal that the emission originates from a TICT state.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19861190519
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  • 20
    Electronic Resource
    Electronic Resource
    Thermal and photochemical reactions of naphtho[1,2,3,4-def]chrysene with 4-Phenyl-1,2,4-triazoline-3,5-dione (1988)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 121 (1988), S. 1647-1650 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Thermische und photochemische Reaktionen von Naphtho [1,2,34-def]chrysen mit 4-Phenyl-1,2,4-triazolin-3,5-dionDie thermischen und photochemischen Reaktionen von Naphtho [1,2,3,4-def]chrysen (1) mit 4-Phenyl-1,2,4-triazolin-3,5-dion (2) werden verglichen. In der thermischen Reaktion führt elektrophiler Angriff von 2 an 1 zum Substitutionsprodukt 4, welches z. T. zu 5 und 6 weiter umgesetzt wird. Unter Lichteinwirkung findet vorzugsweise [4π + 2π]-Cycloaddition von 2 an 1 unter nachfolgender Dehydrierung zu 6 statt; 6 wird durch das Licht zu einem komplexen Gemisch zersetzt, aus dem 10 isoliert werden kann. 5 existiert in zwei atropisomeren Formen. Die Struktur einer dieser Formen, 5b, wurde durch Kristallstrukturanalyse bestimmt.
    Notes: The thermal and photochemical reactions between naphtho-[1,2,3,4-def]chrysene (1) and 4-phenyl-1,2,4-triazoline-3,5-dione (2) have been compared. In the thermal reaction, 2 electrophilically attacks 1 to give substitution product 4 which in part is further transformed into 5 and 6. In the light-induced reaction, 2 predominantly undergoes [4π + 2π] cycloaddition to 1 with subsequent loss of hydrogen to yield 6 which then photodecomposes to give a complex mixture containing 10. 5 exists in two atropisomeric forms. The structure of one form, 5b, was determined by X-ray crystallography.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19881210917
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