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  • 11
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): Chemistry ; Theoretical, Physical and Computational Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: 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.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 12
    Digitale Medien
    Digitale Medien
    Differentiation between isomeric structures of benzazoles by 14N, 13C and 1H NMR (1978)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 11 (1978), S. 385-389 
    Details
    ISSN: 0030-4921
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Nitrogen chemical shifts constitute an effective means of distinguishing between isomeric benzazole ring systems. There is a large difference in nitrogen shielding, usually more than 20 ppm, between isomeric benzenoid- and quinonoid-like structures. 13C and 1H NMR is shown to provide unambiguous structure assignment only in cases of symmetric quinonoid ring systems of azoles.
    Zusätzliches Material: 2 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/mrc.1270110804
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  • 13
    Digitale Medien
    Digitale Medien
    14N and 13C NMR of tautomeric systems of mercapto- and amino-pyridines (1979)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 12 (1979), S. 379-382 
    Details
    ISSN: 0030-4921
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Nitrogen chemical shifts are shown to provide a means of estimating equilibrium compositions of tautomeric systems of mercapto- and amino-derivatives of pyridine. Carbon chemical shifts can afford only qualitative information about such equilibria.
    Zusätzliches Material: 4 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/mrc.1270120611
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  • 14
    Digitale Medien
    Digitale Medien
    Structural studies on mesoionic 1,2,3,4-thiatriazolo-5-aminides and 1,2,3,4-thiatriazolo-5-methylides by nitrogen and carbon NMR (1993)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 31 (1993), S. 447-450 
    Details
    ISSN: 0749-1581
    Schlagwort(e): Nitrogen NMR ; Mesoionic compounds ; Mesoionic thiatriazoles ; Ring-chain valence tautomerism ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 15N, 14N, 13C and 1H NMR data were used for the structural analysis of seven 1,2,3,4-thiatriazoles with various exocyclic groups. Measurements at various temperatures were carried out in order to study the behaviour of exocyclic groups. Some 15N-labelled compounds were prepared to assist in the interpretation of the 15N NMR spectra. The results suggest that the investigated compounds exist in the cyclic structure. Three of the investigated compounds have not been previously synthesized.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/mrc.1260310506
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  • 15
    Digitale Medien
    Digitale Medien
    Conformational behaviour of some trifluoroenaminones by multinuclear magnetic resonance (1993)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 31 (1993), S. 808-814 
    Details
    ISSN: 0749-1581
    Schlagwort(e): Multinuclear magnetic resonance ; Trifluoroenaminone ; Conformation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The structures of 4-N-methylamino and 4-N,N-dimethylamino-1,1,1-trifluorobut-3-en-2-one (1, 2) were solved by means of an analysis of 1H, 1H and 1H, 13C coupling constants. NOE measurements, 13C, 1H heteronuclear correlation and selective decoupling. The spectra of 1 are strongly solvent dependent. Variable-temperature experiments indicated that in these compounds the double bond character of the C—N bond is fairly pronounced and that the p-electrons from the nitrogen atom are engaged in the conjugated π-electron system. 14N, 15N, 17O and 19F chemical shifts for 1 are reported.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/mrc.1260310904
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  • 16
    Digitale Medien
    Digitale Medien
    13C and 15N NMR study of 2,3-diphenyl-1,2,3,4-tetrazolium-5-aminides (1993)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 31 (1993), S. 200-202 
    Details
    ISSN: 0749-1581
    Schlagwort(e): Nitrogen NMR ; Mesoionic compounds ; Chain-ring valence tautomerism ; Structure determination ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 13C, 14N and 15N NMR data are reported for some mesoionic 2,3-diphenyltetrazoles with nitrogen-containing exocyclic groups, and the data confirm their cyclic structures. The protonated forms of these mesoionic structures contain hydrogen atoms at the exocyclic groups.
    Zusätzliches Material: 2 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/mrc.1260310209
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  • 17
    Digitale Medien
    Digitale Medien
    13C and 15N NMR study of mesoionic type A and type B tetrazoles with four nitrogen atoms in the exocyclic group (1994)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 32 (1994), S. 746-748 
    Details
    ISSN: 0749-1581
    Schlagwort(e): NMR ; 15N NMR ; 13C NMR ; Mesoionic compounds ; Tetrazoles ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 13C and 15N NMR measurements are reported from a study of five mesoionic compounds containing either the 2,3-diphenyl- or 1,3-diphenyltetrazolium ring, and either the 2,3-diphenyltetrazolium ring or its linear analogue as an exocyclic group. Three 15N-labelled compounds were synthesized for signal assignment purposes. Some 15N—13C and 15N—15N coupling constants were determined. A proton was found to be located on the exocyclic groups of two of the compounds.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/mrc.1260321208
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  • 18
    Digitale Medien
    Digitale Medien
    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
    Schlagwort(e): NMR ; 1H NMR ; 13C NMR ; 14N NMR ; 15N NMR ; Mesoionic triazoles ; Charge delocalization ; Protonation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 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.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/mrc.1260330209
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  • 19
    Digitale Medien
    Digitale Medien
    Multinuclear magnetic resonance study of some mesoionic 1,3-diphenyltetrazoles with various exocyclic groups (1994)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 32 (1994), S. 284-287 
    Details
    ISSN: 0749-1581
    Schlagwort(e): NMR ; 13C NMR ; 15N NMR ; 14N NMR ; Mesoionic compounds ; Tetrazoles ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 1H, 13C, 14N and 15N NMR methods were applied to the study of some Type A mesoionic 1,3-diphenyltetrazoles with various exocyclic groups. The ring structures of these tetrazoles are confirmed by the nitrogen NMR data. The shielding of N-4 increases consecutively by amounts of ca 10 ppm as the bonded exocyclic atom changes from S to C to O.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/mrc.1260320505
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  • 20
    Digitale Medien
    Digitale Medien
    Multinuclear NMR study of protonation in some indolizine systems (1994)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 32 (1994), S. 373-375 
    Details
    ISSN: 0749-1581
    Schlagwort(e): NMR ; Nitrogen ; NMR ; Indolizines ; Protonation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 1H, 13C and 15N NMR data are presented for seven indolizine derivatives in solutions of dimethyl sulphoxide and trifluoroacetic acid (TFA). The TFA solutions contain species protonated at position N-1 in all cases. The most definitive evidence for the site of protonation is provided by the 15N results.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/mrc.1260320613
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