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  • 1
    Electronic Resource
    Electronic Resource
    (E, Z)1-Equilibria, 17 Demonstration of the Nitrogen Inversion Mechanism of Imines in a Schiff Base ModelDedicated to Professor Heinrich Nöth on the occasion of his 65th birthday. (1993)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 747-754 
    Details
    ISSN: 0009-2940
    Keywords: Diastereotopomerization, (E, Z) ; Imines ; Inversion, nitrogen ; Permethylation ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Experimental differentiation between pure C=N double bond rotation and nitrogen inversion in N1-arylimines is possible with a single compound (13b) under the proviso of slow rotation about the N-aryl single bond. Labelling by 1H and 13C nuclei at the diastereotopic faces of the C=N moiety as well as of the N-aryl group is the clue to a successful stereodynamic analysis, as performed by variable-temperature NMR spectroscopy of 13b, a sterically congested and chiral model compound. Interpretation of similar measurements on a second model (13d) is less straightforward. The experimental observation of time-averaged Cs symmetry by NMR coalescences is only compatible with a mechanism of (E/Z) stereomutation either by pure inversion at sp2 nitrogen or by a contribution from C=N rotation together with a synchronized (geared) controtation about the N-aryl single bond. However, the latter combination is concluded to be predominantly inversion-like by comparisons with related imines.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19931260327
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  • 2
    Electronic Resource
    Electronic Resource
    (E,Z) Equilibria, 14. Substituent-Induced Chemical Shifts along the C = N Bond of Schiff Bases (1992)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 125 (1992), S. 2033-2040 
    Details
    ISSN: 0009-2940
    Keywords: 13C NMR, SCS ; Substituent effects ; Imines ; Isomerization, (E,Z) Schiff bases ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Sterically congested N-(1,1,3,3-tetraalkyl-2-indanylidene)-amines 8-11, N-(cyclopentylidene)anilines 13-17, and two of their salts are described, together with a short synthesis of 2-imino-1,1,3,3-tetramethylindan (5). Some of these imines show rapid (E,Z) equilibration. Positively and negatively charged nitrogen functions (in 6 and 7) cause opposite 1H- and 13C-NMR chemical shift effects along the C = N bond. Chemical shifts are almost equally affected by the lone electron pair and by the imino N-H bond. Substituent-induced chemical shifts (SCS) have been assigned for all syn and anti positions with respect to methyl, phenyl, and 2,6-dimethylphenyl groups at the imino nitrogen atom. The structurally well-defined, rigid imines recommend themselves as new models for the calibration of theoretical approaches to syn/anti-differentiating SCS.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19921250911
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