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  • 1
    ISSN: 0935-6304
    Keywords: Resolution of atropisomers ; Alkylated biphenyls ; Polychlorinated biphenyls (PCBs) ; Dynamic gas chromatography ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Selectively alkylated cyclodextrins have been used to resolve the enantiomers of 2,2′ alkylated biphenyls. The configurational stability of 2,2′-dimethyl and 2,2′-diethyl biphenyls is insufficient for gas chromatographic separation even at ambient temperature. 2-Isopropyl-2′-t-butyl- and 2,2′-di-t-butylbiphenyl are configurationally stable under the conditions applied, whereas 2,2′-diisopropyl- and 2,2′-bis(trifluoromethyl)biphenyl show temperature-dependent interconversion of the enantiomers during chromatography. The gas chromatographic separation of the enantiomers of some ortho trichlorinated biphenyls carrying 4, 5, and 6 chlorine substituents has been demonstrated for the first time.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0947-3440
    Keywords: Atropisomers ; Biphenyls, axially chiral ; Enantiomerization ; Dynamic gas chromatography ; Polarimetry ; Energy barriers ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have synthesized a series of 2,2′-substituted biphenyls and particularly derivatives of 2,2′-bis(trifluoromethyl)biphenyl (4) with either one or two fluoro, chloro, bromo, amino, nitro or methoxy substituents in the para positions for investigating the influence of these substituents on the rotational energy barrier of the biphenyls by polarimetry and dynamic gas chromatography (DGC). Axially chiral biphenyls with at least two bulky substituents in the ortho positions were separated by gas chromatography on selectively modified cyclodextrins. Due to competition between resolution and enantiomerization in the gas chromatographic column 2-tert-butyl-2′-isopropyl- (2), 2-isopropyl-2′-(trifluoromethyl)biphenyl (5), and some para-substituted derivatives of 4 show temperature-dependent interconversion profiles and coalescence phenomena in analogy to dynamic NMR studies. The accelerating effect on the rate of enantiomerization of electron-donating groups in the para positions and the decelerating effect of electron-accepting groups has been determined. Dynamic gas chromatography is shown to be a useful supplement to studies of thermal enantiomerization kinetics of optically enriched or separated compounds by polarimetry for the investigation of energy barriers of atropisomeric biphenyls.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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