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  • 1
    Electronic Resource
    Electronic Resource
    X-ray diffraction study of some indolinones (1995)
    Springer
    Journal of chemical crystallography 25 (1995), S. 299-308 
    Details
    ISSN: 1572-8854
    Keywords: Indolinone ; lactam ; cis-amide ; X-ray ; hydrogen bond chains
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract X-ray diffraction studies are reported for six indolinones. The results show that two different types of associates are present in the crystal state of the compounds having an NH group. The indolinone molecules without any substituents form cyclic dimers while those with one or two methyl groups attached to the C3 atom of the lactam ring form infinite hydrogen bonded chains. It is confirmed that the lactam moiety forms a typical planar amide structure with no sign of the enol form present.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01796054
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  • 2
    Electronic Resource
    Electronic Resource
    An X-ray study of some 2,3-diphenyltetrazolium salts (1995)
    Springer
    Journal of chemical crystallography 25 (1995), S. 29-35 
    Details
    ISSN: 1572-8854
    Keywords: X-ray diffraction ; aromatic structure ; tetrazole ring
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract An X-ray diffraction study is reported for three molecules of salts containing a cation with a positive charged 2,3-diphenyltetrazolium ring. The results confirm aromatic structure of the tetrazole ring and the delocalization of charge on the whole molecules of the cations. The molecular geometry obtained is compared with that for free mesoionic 2,3-diphenyltetrazoles which have already been studied and the ring parameters do not reveal significant differences. But is shows that the geometry of the (NNO)− exocyclic group is changed as a result of alkylation. Compound I C13H12N5Cl, P21/a,a=16.934(4),b=6.575(1),c=26.121(4) Å, β=108.15(2)°, II C14H13N6OI, P312,a=10.774(3),c=12.821(4) Å, IV C26H20N8Cl2, C2/c,a=22.316(4),b=6.6903(7),c=20.437(3) Å, β=92.51(1)°.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01666191
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  • 3
    Electronic Resource
    Electronic Resource
    Mesoionic compounds — structure and NMR parameters (1995)
    Springer
    Chemistry of heterocyclic compounds 31 (1995), S. 1027-1046 
    Details
    ISSN: 1573-8353
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract It has been shown that1H,13C,14N,15N,17O, and77Se NMR are very successful techniques for the identification and investigation of potential valence tautomerism in all types of mesoionic compounds. Especially the combined use of14N and15N NMR studies has been shown to be very effective in solving structural problems. From15N NMR it is possible to obtain accurate chemical shifts and spin-spin couplings, whereas the14N NMR spectra provide us with nuclear relaxation and some chemical shift data. In particular14N NMR is very useful for the identification of charged nitrogen atoms in molecules containing non equivalent nitrogen positions. This information is available from the relative14N signal widths, which depend upon the rates of14N relaxation, positively charged nitrogen atoms usually have relatively slow14N relaxation rates thus giving rather sharp NMR signals. Some solid state, CP MAS,13C and15N NMR results are available for comparison with the solution NMR data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01165049
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  • 4
    Electronic Resource
    Electronic Resource
    Multinuclear magnetic resonance study of some mesoionic oxatriazoles containing nitrogenous exocyclic groups (1995)
    Springer
    Chemistry of heterocyclic compounds 31 (1995), S. 1103-1107 
    Details
    ISSN: 1573-8353
    Keywords: 1H,13C,14N, and15N NMR ; chemical shifts ; line widths ; mesoionic oxatriazoles ; charge localization ; valence tautomerism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract 1H,13C,14N and15N NMR measurements are reported for four mesoionic 1-oxa-2, 3, 4-triazoles containing exocyclic nitrogenous groups. The NMR signal assignments are discussed and compared with those previously published for some corresponding oxatriazoles. The results obtained support the proposed cyclic mesoionic structures for the compounds studied. The questions of possible charge delocalization and valence tautomerism are addressed. Compound with N− H as a exocyclic group (Fig. 1) is found to be relatively unstable, this is attributed to proton migration in the corresponding non-cyclic form of this molecule.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01165057
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  • 5
    Electronic Resource
    Electronic Resource
    Multinuclear, variable-temperature NMR study of hydrogen bonding in two ortho-Mannich bases (1995)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 8 (1995), S. 463-467 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 1H and 13C NMR data for 2-diethylaminomethyl-3,4,6-tri- and -tetrachlorophenols in CH2Cl2 solutions at a variety of temperatures are reported. The results are consistent with intramolecular hydrogen bonding and proton transfer as shown in the structure 3. Concentration dependence of the NMR data for the perchloro compound shows an additional hydrogen bonding process attributed to the solute self-association. The 1H, 13C and 15N NMR data support the proposed proton transfer structure.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610080704
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  • 6
    Electronic Resource
    Electronic Resource
    Nitrogen-15 NMR studies of hydrogen bonding and proton transfer in complexes of pyridine N-oxides with dichloroacetic acid in CDCl3 (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 746-750 
    Details
    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The 15N NMR chemical shifts of eight substituted pyridine N-oxides (B) and their complexes (AHB) with methanol and dichloroacetic and trifluoromethanesulfonic acids were measured in chloroform-d at the natural abundance level. The measured chemical shifts are strongly affected by substituents, hydrogen bond strength and protonation. The plot of the relative chemical shifts, Δδ(15N) = δ(AHB) - δ(B), against ΔpKa gives a titration curve that reflects the variation of the hydrogen bond strength and the proton moves from the acid to the N-oxide. According to previous IR data, in the complexes from the inversion region (ΔpKa = 1·26), the proton is either delocalized (B…H…A) or more likely the lifetime is so short (≤10-13 s) that the method does not recognize the B…H-A and B+H…A- species. Protonation of pyridine N-oxides shifts the nitrogen signal ca 50 ppm to lower frequencies compared with the ca 123 ppm for pyridines.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 7
    Electronic Resource
    Electronic Resource
    Multinuclear magnetic resonance study of some mesoionic 1,3,4-triazoles (1995)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 33 (1995), S. 134-137 
    Details
    ISSN: 0749-1581
    Keywords: NMR ; 1H NMR ; 13C NMR ; 14N NMR ; 15N NMR ; Mesoionic triazoles ; Charge delocalization ; Protonation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1H, 13C, 14N and 15N NMR data are reported for a series of mesoinoic 1,3,4-triazoles and some of their salts. The results obtained show that the molecules studied exist in the cyclic mesoionic form with delocalization of the positive charge over the ring atoms. The corresponding negative charge occurs on the atoms of the exocyclic groups, which also act as the site of protonation and salt formation. The most important experimental data for these interpretations are found to be the nitrogen shieldings and that for C-5.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260330209
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