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  • 1
    Electronic Resource
    Electronic Resource
    What is the basic chromophore of a dye? (1984)
    Springer
    Monatshefte für Chemie 115 (1984), S. 21-34 
    Details
    ISSN: 1434-4475
    Keywords: Dye ; Colour and constitution ; Chromophore ; Streptopolymethine ; Computation ; PPP ; MIM ; MOA ; CA ; FMO ; MINDO/3, QCFF/Pi
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die Farbe des 4,5-diphenyl-substituierten 2-Dimethylamino-3-azacyclopentadienons (4) wird im Hinblick auf verschiedene Grundchromophore diskutiert. Der Grundchromophor kann entweder mit der Struktur identifiziert werden, welche die gleiche Absorptionswellenlänge wie die betrachtete Verbindung aufweist, oder mit der Struktur, welche elektronisch am stärksten mit dem Farbstoff verwandt ist. Im Falle4 führen beide Betrachtungen zu verschiedenen Ergebnissen. Auf Grund des Korrelationsdiagramms der Elektroenzustände, die in die Anregung eingeschlossen sind, wird die langwellige Absorption von4 besser verstanden als Merocyaningrundchromophor, als durch eine betainische Teilstruktur, welche die gleiche Farbe wie4 aufweisen sollte und nachKlessinger der Grundchromophor ist. Diese Schlußfolgerung wird aus derPPP-Konfigurationsanalyse der Wellenfunktion von4 in bezug auf verschiedene molekulare Teilstrukturen gezogen. Die durch Geometrieoptimierung in MINDO/3 und QCFF/Pi-Näherung berechnete Molekülgeometrie lieferte zusätzlich Argumente zugunsten der Cyclomerocyaninstruktur von4. Bezüglich der Farbe kann4 zu einer neuen Serie cyclisch-konjugierter Chromophore gerechnet werden.
    Notes: Abstract Taking the 4,5-diphenyl-substituted 2-dimethylamino-3-azacyclopentadienone (4) as an example its colour has been discussed in relation to different basic chromophores (parent chromophores). The parent chromophore can be defined either as the structure which has nearly the same absorption wavelength as the dye under consideration or as the substructure which is electronically most closely related to the dye. In the case of4 both considerations lead to different results. Based on the correlation diagram between the electronic states involved in the electronic excitation the long-wavelength absorption of4 is better understood in terms of the merocyanine parent chromophore than in terms of a betainic substructure, which should have the same colour as4 and is the parent chromophore according toKlessinger. This conclusion is drawn fromPPP configuration analysis of the wavefunctions of4 relative to different molecular substructures. The molecular geometry predicted by the geometry-optimized MINDO/3 and QCFF/Pi calculations provided additional arguments in favour of the cyclomerocyanine structure of4. In respect to the colour4 belongs to a new series of cyclic-conjugated chromophoric systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00798418
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  • 2
    Electronic Resource
    Electronic Resource
    Zur Farbigkeit der Pseudooxo-Krokonsäurebisamide (1985)
    Springer
    Monatshefte für Chemie 116 (1985), S. 625-632 
    Details
    ISSN: 1434-4475
    Keywords: Colour and constitution ; Chromophore ; Oxo croconic acid bisamide ; Pseudooxo croconic acid bisamide ; Electronic wavefunctions and transitions ; PPP
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The colour of oxo- und pseudooxo croconic acid bisamides (1) in solution is due to two intense π → π* transitions in the visible region. These transitions are related to those of the Klessinger-Lüttke basic indigo chromophore. The first band corresponds to the second absorption band of this basic chromophore red-shifted by the intramolecular charge transfer excitation between the molecular subsystems of1. The second band of1 is closely related to the colour band of the basic indigo chromophore. According to the results of various analysis and projection techniques the interpretation of the colour of1 in terms of the basic indigo chromophore is superior to any other one in terms of alternative chromophoric subsystems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00798787
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  • 3
    Electronic Resource
    Electronic Resource
    Substituent Effects on the Vinylcyclopropane-Cyclopentene Rearrangement - A Theoretical Study by Restricted and Unrestricted Density Functional Theory (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 215-220 
    Details
    ISSN: 1434-193X
    Keywords: Density functional calculations ; Vinylcyclopropane-cyclopentene rearrangement ; [1,3]-Sigmatropic shift ; Biradical-like transition structure ; Substituent effects ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The effect of donor substitution by the hydroxy group and of acceptor substitution by the cyano group on the activation energies of the vinylcyclopropane-cyclopentene rearrangement was calculated by the spin-restricted RB3LYP/6-31G* method for reactant structures and by the spin-unrestricted UB3LYP/6-31G* method for transition structures. The activation energies of the rearrangement of hydroxy- and cyano-substituted vinylcyclopropanes are very similar for substitution in the same position. In agreement with earlier findings the substituent effects on the activation energies are closely connected with the radical stabilizing properties of the substituents. As indicated by singlet/triplet splitting energies, the transition structures are essentially biradicaloid. In spite of spin pairing in the transition structure the substituent effects on bond lengths and on stabilization energies are very similar to those of the free radicals corresponding to the two radical substructures. Thus, the transition structures may be considered, in good approximation, as structures consisting of two weakly interacting radicals.Supporting information for this article is available on the WWW under -http://www.wileY-Vch.de/contents/jc_2046/1999/98349_s.pdf or from the author.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [1,3]-Sigmatropic Rearrangements of Divinylcyclopropane Derivatives and Hetero Analogs in Competition with Cope-Type Rearrangements - A DFT Study (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1107-1114 
    Details
    ISSN: 1434-193X
    Keywords: Rearrangements ; Density functional calculations ; Substituent effects ; Transition structures ; Small-ring compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Two possible types of competing [1,3] rearrangements of divinylcyclopropane derivatives and of the hetero-analogous compounds vinylcyclopropanecarbaldehyde and vinylcyclopropanecarbthioaldehyde to five-membered ring compounds have been investigated theoretically by (U)DFT (Becke3LYP/6-31G*) methodology. Although both of the rearrangement pathways correspond to a reaction of the monosubstituted cyclopropane substructure, i.e. a reaction of vinylcyclopropane or of cyclopropanecarb(thio)aldehyde, new features in the reactivity are seen due to the combination of two substituents. Reaction parameters such as reaction and activation energies of the [1,3]-sigmatropic rearrangements have been calculated and compared. Substituent effects of hydroxy and formyl (donor and acceptor) groups in specific positions have also been considered. On the basis of these calculations, the [1,3] rearrangement of vinylcyclopropanecarbaldehydes to dihydrofurans can be expected to be kinetically favored over their conversion to cyclopentenes, while formation of the latter should be favored thermodynamically. This prediction is borne out by the experimental findings. Depending on the substitution pattern, the [1,3]-sigmatropic rearrangement of vinylcyclopropanecarbaldehydes may compete with the [3,3]-sigmatropic rearrangement. For the other investigated structures, the [1,3] rearrangement is strongly disfavored.Supporting information for this article is available on the WWW under -http://www.wileY-Vch.de/contents/jc_2046/1999/98456_s.pdf or from the author.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    A DFT Study on the Vinylcyclopropanecarbaldehyde-to-2,5-Dihydrooxepin Hetero-Cope-type Rearrangement and on Related ReactionsDedicated to Prof. Dr. Klaus Hafner on the occasion of his 70th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 2443-2449 
    Details
    ISSN: 0947-3440
    Keywords: Pericyclic reactions ; Hetero-Cope-type rearrangement ; Cyclopropanes ; Heterocycles ; Substituent effects ; Transition structures ; Density functional calculations ; Ab initio calculations ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The prototypical 1,2-cis-vinylcyclopropanecarbaldehyde-to-2,5-dihydrooxepin hetero-Cope-type rearrangement was studied by “exact” first-principle methods. The reaction pathway was examined. The reaction, as well activation energies, was calculated for the unimolecular transformation of vinylcyclopropanecarbaldehyde and various derivatives. The derivatives differ from vinylcyclopropanecarbaldehyde by replacement of the formyl (CH=O) by the thioformyl (CH=S) or formiminyl (CH=NH) group and, in part, by replacement of hydrogen atoms at the substituted carbon atoms of the cyclopropane ring by hydroxyl or formyl substituents. The experimental reaction parameters of vinylcyclopropanecarbaldehyde are surprisingly well reproduced by B3LYP/6-31G* density functional and MP2/6-31G* ab initio quantum theoretical calculations. Reactant and product are nearly isoenergetic, while the activation energy amounts to about 25 kcal/mol. In the case of the nitrogen and sulfur containing compounds the isomeric seven-membered ring structures are considerably favoured over the cyclopropanes. Due to a low calculated activation energy a rapid formation of the 2,5-dihydrothiepin is expected. Substitution of the hydrogen at the substituted ring carbon atoms in vinylcyclopropanecarbaldehyde by OH and CH=O also lowers the barrier and increases, in general, the exothermicity of the reaction. As shown by the reaction energies of isodesmic reactions both reactants and products are stabilized by substitution. However, the seven-memberd ring compounds are more strongly stabilized than the cyclopropanes. The OH group exerts a different effect depending on whether the linkage is geminal or vicinal to the C=X group. The difference is caused by hydrogen bond formation in geminal arrangements. The substituent effects in the cyclopropane series parallel those for the prototypical Cope-type and Claisen-type series. The particular feature of the cyclopropane series is the lower stability of the cyclopropanes relative to the corresponding open chain congeners. This is obviously due to the ring strain which over-compensates for attractive interactions between cyclopropane and the substituents. In consequence, the formation of seven-membered ring compounds proceeds more easily than the formation of the corresponding compounds in related Cope-type rearrangements.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719971207
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