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  • 1
    Electronic Resource
    Electronic Resource
    N-amination of 2,6-di-tert-butylpyridine (1994)
    Springer
    Monatshefte für Chemie 125 (1994), S. 35-41 
    Details
    ISSN: 1434-4475
    Keywords: 2,6-Di-tert-butylpyridine ; N-Amination ; 1-Amino-2,6-di-tert-butylpyridinium perchlorate ; Steric hindrance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Trotz seiner geringen Nucleophilie ist an 2,6-Di-tert-butylpyridin (DTBP) leicht eine N-Aminierung durchzuführen. Andere gehinderte Pyridine reagieren ähnlich. Ein Vergleich der NMR-Kohlenstoffverschiebungen von 2,6-disubstituiertem 1-Aminopyridiniumperchlorat mit denjenigen der entsprechenden 1-Methylpyridiniumsalze zeigt, daß die Änderungen parallel verlaufen. 1-Amino-2,6-di-tert-butylpyridiniumperchlorat reagiert nicht mitp-Dimethylaminobenzaldehyd, hingegen wurden andere gehinderte 1-(4′-Dimethlylaminobenzylidenamino)pyridiniumsalze über Standardmethoden erhalten.
    Notes: Summary Despite its low nucleophilicity 2,6-di-tert-butylpyridine (DTBP) easily undergoes N-amination. Other hidered pyridines react similarly. Comparison of the NMR carbon chemical shifts of 2,6-disubstituted 1-aminopyridinium perchlorates and those of the respective 1-methylpyridinium salts shows that the changes are parallel. 1-Amino-2,6-di-tert-butylpyridinium perchlorate does not react withp-dimethylaminobenzaldehyde. However, other hindered 1-(4′-dimethylaminobenzylideneamino)pyridinium salts were obtained by a standard procedure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00811671
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  • 2
    Electronic Resource
    Electronic Resource
    Electron impact-induced fragmentation of some aminonitropyridines (1991)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 26 (1991), S. 100-104 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The fragmentation behaviour of 18 vicinally substituted aminonitropyridines was studied under electron impact conditions. Tbe decomposition patterns were found to be strongly dependent on the position of substituents. The formation of the aza analogue of carbazole seems to affect considerably the fragmentation of 3-nitro-2-phenylaminopyridine.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210260211
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  • 3
    Electronic Resource
    Electronic Resource
    The mass spectra of some vicinally substituted nitropyridines (1989)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 24 (1989), S. 133-138 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The fragmentation behaviour of 22 vicinally substituted nitropyridines has been studied under electron impact conditions. The decomposition patterns were found to be strongly affected by interaction of the substituent with the nitro group and the ring nitrogen. AH fragmentation sequences depend to a great extent on the position of the substituent in the ring.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210240213
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  • 4
    Electronic Resource
    Electronic Resource
    Crystal and moecular structure of N-nitro-N-methyl-p-nitroaniline: Analysis of substituent effects on the ring geometry and estimation of the Hammett substituent constant for the N-methylnitramino group (1993)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 6 (1993), S. 257-260 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The crystal and molecular structure of N-nitro-N-methyl-p-nitroaniline was solved with good precision: R = 0·058 and average estimated standard deviation for bond lengths = 0·003 Å. Analysis of the geometry reveals that the NO2 attached to the N atom is strongly conjugated. Application of the HOSE model to its geometry and to geometries of 12 other para-substituted nitrobenzenes yields good linear regressions between canonical structure weights and Hammett σ values by interpolation, σ for the N(Me)NO2 group is estimated to 0·36.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610060502
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  • 5
    Electronic Resource
    Electronic Resource
    The tautomerism of nitraminopyridines (1995)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 8 (1995), S. 689-695 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 1H, 13C and 15N NMR data for nitraminopyridines are discussed in terms of tautomeric equilibria in these compounds. The favoured tautomer is determined mainly from 15N NMR spectroscopy. The chemical shift of the nitrogen atom of the nitro group in nitraminopyridines and N-nitroanilines which cannot tautomerize vary from 28·0 to 35·4 ppm in DMSO solution. 3-Nitraminopyridine and 2-nitramino-3- and -5-nitropyridines behave similarly. In the 15N NMR spectra of nitrimino-1-methyldihydropyridines, used as models, an upfield shift of that atom, different from that observed for 2-nitraminopyridine, indicates the significance of the nitrimino tautomer. In contrast, a downfield shift of the ring nitrogen atom of some other compounds shows an increased weight of the nitramino tautomer. 3-Nitraminopyridine, when dissolved in DMSO, does not have the zwitterionic structure. Changes in the chemical shift of the amino nitrogen atom are not readily interpreted. Some proton and carbon chemical shifts and hydrogen-hydrogen and carbon-hydrogen spin-spin coupling constants can also be used to determine the predominant tautomer of 2- and 4-nitraminopyridines.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610081007
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  • 6
    Electronic Resource
    Electronic Resource
    Transmission of electronic effects in 4-aryl-2,6-diphenylpyrylium perchlorates and related compounds (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 631-638 
    Details
    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Substituent effects on the 13C NMR spectra of 4-aryl-2,6-diphenylpyrylium and 1-methyl-4-aryl-2,6-diphenylpyridinium perchlorates and 4-aryl-2,6-diphenylpyridines were investigated. The dual substituent parameter approach indicates that the resonance contribution to the carbon chemical shifts in the para position to the substituent in the 4-aryl moiety is comparable to that for 4-R-biphenyls. Although heterocyclic moieties jointed at the para position with respect to the substituent in the 4-aryl group differ in their deactivating power, they diminish the resonance term to the same extent in each series. This may result in conformational variations of the compounds studied. AM1 calculations were used to explain the chemical shifts observed.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    13C NMR study of the substituent effects in ortho-substituted nitrobenzenes (1992)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 30 (1992), S. 740-745 
    Details
    ISSN: 0749-1581
    Keywords: 13C NMR ; ortho-Substituted nitrobenzenes ; Substituent effects ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 13C NMR chemical shifts of 22 ortho-substituted nitrobenzenes are reported. Except for those on C-3 and C-5, the effects of the interacting nitro group and the substituent are non-additive. The chemical shifts of the ipso, ortho and para carbons in the spectra and those of monosubstituted benzenes are linearly dependent. Multiparameter correlation analysis shows a predominant field/inductive effect on the ipso compared with both the ortho and para carbon chemical shifts. It shows that the Reynolds non-electronic factors evaluate the substituent chemical shifts of the ipso and ortho positions much better than the Charton steric parameters. Moreover, both in ortho- and para-substituted nitrobenzenes the substituent exerts almost the same shift on the ipso carbon atom. This suggests that the studied compounds, except those carrying very bulky groups, show a high tendency to be planar.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260300809
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  • 8
    Electronic Resource
    Electronic Resource
    1H, 13C and 17O NMR study of substituted nitropyridines (1991)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 29 (1991), S. 878-884 
    Details
    ISSN: 0749-1581
    Keywords: 1H NMR chemical shifts and coupling constants ; 13C NMR chemical shifts and coupling constants ; 17O NMR chemical shifts and line widths ; Substituted 2- and 3-nitropyridines ; Molecular mechanics calculations ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1H, 13C and 17O NMR spectra for 22 substituted nitropyridines were measured and their 1H NMR spectra were analysed. The most significant variations in the NMR parameters are found for isomeric hydroxy derivatives, owing to the possibility of keto-enol tautomerism. The prevalence of the keto form is observed in 2- and 4-hydroxy derivatives, while the 3-hydroxy derivative exists in its enol form. Among the three nuclei studied, 17O seems to be the best nucleus for probing the keto-enol tautomerism. No correlation is observed between the torsion angle of the nitro group and its 17O NMR chemical shift. Molecular mechanics calculations were performed to clarify the torsional energetics of the nitro group and the preferences for keto-enol tautomerism.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260290904
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  • 9
    Electronic Resource
    Electronic Resource
    Effect of the ortho-nitro group on the 13C NMR chemical shifts of substituted pyridines (1993)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 31 (1993), S. 38-44 
    Details
    ISSN: 0749-1581
    Keywords: 13C NMR ; Nitropyridines ; Substituent effects ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 13C NMR spectra of 40 vicinally substituted 2- and 3-nitropyridines were recorded. The observed chemical shifts are, in general, non-additive. These results are discussed in terms of the effects of 2-, 3- and 4-substitutents on the ring carbons and of the position of the fixed nitro group and the substituent. The chemical shifts of the para carbon, with respect to the substitutent, follow well the dual substituent parameter approach, which shows their electronic origin. However, the substituent chemical shifts of both ipso and ortho positions can be rationalized, in terms of multiple parameter substituent correlation analysis, only on a approximate level.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260310108
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  • 10
    Electronic Resource
    Electronic Resource
    Nitramino, NRNO2 (R = H, CH3), as a substituent. 13C and 15N NMR spectroscopic study of nitraminobenzenes and -pyridines (1993)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 31 (1993), S. 659-664 
    Details
    ISSN: 0749-1581
    Keywords: Nitraminobenzenes ; -pyridines ; 13C ; 15N NMR chemical shifts ; nJ(13C,1H) spin-spin coupling constants ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to clarify the special properties of the aryl-bound nitramino substituent NRNO2 (R = H, CH3), 13C and 15N NMR spectra of six nitraminobenzenes and nine nitraminopyridines were measured in DMSO-d6 and their chemical shifts assigned. 1H NMR chemical shifts and spin-spin coupling constants of all the compounds were also determined. In contrast to the behaviour of nitropyridines or -benzenes studied previously, most of the present compounds gave very broad 17O NMR lines even at elevated temperatures and their 17O NMR data were not useful for any reliable conclusions.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260310711
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