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  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1491-1509 
    ISSN: 1434-193X
    Keywords: Chirality ; Circular dichroism ; Cyclophanes ; Theoretical calculations ; Strained molecules ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chiroptical properties of planar-chiral and helical molecules without stereogenic centres and with well-defined structure, strain, electronic properties and chirality are investigated by experimental and theoretical circular dichroism spectroscopy. We report on the synthetic and theoretical achievements made during the past 10 years in the field of rigid [2.2]metacyclophane propellers, as well as in the area of [n]para- and [n]metacyclophanes containing aliphatic parts like adamantane or unsaturated bridges. Results for carbo and hetero helicenes and helicene-related molecules like twisted phenanthrenes are presented. It is demonstrated how reliable theoretical calculations using configuration interaction and time-dependent methods in combination with density functional theory today are and how useful the interplay between theory and experiment stimulates the development of chiral molecules optimized for this purpose. Even for large molecules it is routinely possible to assign Cotton effects to electronic transitions, to evaluate chromophore contributions, to determine absolute configurations and conformational equilibria, and to discover intramolecular charge transfer effects.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2003-2007 
    ISSN: 1434-193X
    Keywords: Supramolecular chemistry ; Rotaxanes ; Mechanical bond ; Molecular recognition ; Chirality ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this paper we report on amide rotaxanes with tetrabenzoylglucose stoppers. When acetyl groups are used instead of benzoyl groups, merely a pseudo-rotaxane 5 is obtained. The circular dichroism measurements of the rotaxanes 6a and 6b differ significantly from that one of the free axle 7. Similarly, the Cotton effects of the mixtures of achiral wheels 2a and 2b and chiral axle indicate intermolecular host-guest interactions, likewise. After an addition of a solution of NaOMe the wheel is slipping off immediately and quantitatively by hydrolysis, as the benzoylglucose stoppers decrease in size by hydrolysis.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    ISSN: 0009-2940
    Keywords: Chirality ; Chromium complexes ; Helicity ; Configuration (absolute) ; [2.2]Metacyclophanes ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Tricarbonylchromium Complexes of Chiral [2.2]Metacyclophanes: Syntheses, Structures, and Chiroptical PropertiesHPLC-baseline separations of three racemic cyclophanes 3, 4, and 6 on cellulose tris(3,5-dimethylphenyl)carbamate led to their enantiomers with high optical purity. Complexation of (-)-3 and (+)-3 with triamminetricarbonylchromium yielded chiral Cr(CO)3 complexes (-)-(S)P-(3S)M-3a and (+)-(R)P-(3R)M-3a stereoselectively. Derivatisation of the complexes by lithiation and reaction with electrophiles gave new substituted chiral Cr(CO)3 complexes of [2.2]metacyclophanes regio-selectively. X-ray structure analyses of one chiral chromium complex (-)-(R)P-(5S)M-14a and three chiral chromium-free ligands (-)-(S)P-3, (-)-(S)P-4, and (-)-(S)P-6 led to the assignment of the absolute configurations of all chiral compounds discussed here. The influences of substituents on the chiroptical properties are investigated. The helicity of [2.2]metacyclophanes is discussed. For the first time X-ray structure analyses were performed of a bis-Cr(CO)3 complex (9a) as well as of the first chromium complex 10a of a heteraphane. Dethioketalisation of (-)-(S)P-3 with NBS gave (-)-(S)P-18, the absolute chirality of which has been known, under retention of configuration.
    Additional Material: 17 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    ISSN: 0009-2940
    Keywords: Carbene complexes ; Chromium ; Cyclophanes ; Chirality ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pentacarbonyl(4-[2.2]metacyclophanyl(methoxy)carbene)-chromium(0) (6) was prepared according to the Fischer route from 4-bromo[2.2]metacyclophane. Aminolysis with non-chiral and chiral amines affords aminocarbene complexes 7-12. X-Ray structure analyses for 6 and its aminocarbene analogs 7 and 8 indicate that the incorporation of the chromium-carbene fragment has no significant influence on the deformation of the [2.2]metacyclophane skeleton.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    ISSN: 0009-2940
    Keywords: Chirality ; Circular dichroism ; Conformational mobility ; Cyclophanes ; [n]Phanes ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Deformed Chiral [n]MetacyclophanesThe new dithiametacyclophane 3c and the thiaazametacyclophanes 6a, b are chiral, but do not contain chirality centres. They are obtained by cyclization of 1,3-propanedithiol (2), or of the thiaza precursors 5a, b, with the bis(bromomethyl) compounds 1, 4a, b. The dynamic behaviour of the aliphatic chains in 3c, and 6a, b (flipping/rotation) have been studied by dynamic NMR. X-ray analyses of 3c and 6a document the out-of-plane deformation of the boat-shaped benzene ring. The circular dichroism of enantiomer-enriched 3c is reported.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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