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  • 1
    Digitale Medien
    Digitale Medien
    Electron impact and chemical ionization mass spectra of bis(methoxycarbonyl) [2.2](2,5)pyridinophanes. Formation of quinolizinium ions under electron impact (1986)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 21 (1986), S. 367-370 
    Details
    ISSN: 0030-493X
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: For four isomeric bis(methoxycarbonyl)[2.2](2,5)pyridinophanes differing only in the mutual orientation of the two nicotinic ester units, electron impact mass spectra were measured. The fragmentations observed distinguish surprisingly well between the isomers, depending on the transannular substitution pattern. Of special interest is that for one isomer the otherwise unimportant ion at m/z 298 is found as base peak. This ion is formed by expulsion of HCN from the molecular ion, transannular cycloaddition and aromatization to a stable quinolizinium ion. Fragmentation pathways of the isomers are compared, and chemical ionization and negative ion chemical ionization mass spectra are discussed.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/oms.1210210612
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  • 2
    Digitale Medien
    Digitale Medien
    Proximity effects in the mass spectra of crowded bis(dimethylamino)arenes: Part II - Rearrangements of the molecular radical cations of ‘proton sponges’ by reciprocal methyl/hydrogen transfer (1989)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 24 (1989), S. 367-372 
    Details
    ISSN: 0030-493X
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The EI induced fragmentation pathways of 4,5-bis(dimethylamino)fluorene, 4-(d6-dimethylamino)-5-(dimethylamino)fluorene, 4,5-bis(d6-dimethylamino)fluorene, 4-(dimethylamino)-5-methylaminofluorene, 4,5-bis-(methylamino)fluorene, 4-amino-5-methylaminofluorene, 1,8-bis(dimethylamino)naphthalene, 1,8-bis(d6-dimethyl-amino)-naphthalene and 1,8-bis(dimethylamino)-2,7-dimethoxynaphthalene were investigated. A mechanism is pro-posed for the surprising elimination of CH3—NH2 from the molecular ion, followed by loss of C2H5·, C2H4 and CH3CN and for the accompanying cyclizations to stable heterocyclic ions: prior to fragmentation the molecular radical ion rearranges to new, distonic radical ions by reciprocal H and CH3 transfers between the adjacent dimethylamino groups. Each of these new, isomeric molecular ions decomposes subsequently in a characteristic way.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/oms.1210240602
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  • 3
    Digitale Medien
    Digitale Medien
    Application of 1H/13C inversely correlated NMR spectroscopy to the determination of the stereochemistry of a polysubstituted [2.2]paracyclophane (1988)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 26 (1988), S. 834-838 
    Details
    ISSN: 0749-1581
    Schlagwort(e): 4,7-Dichloro-5,8,12,15-tetramethoxy-13,16-bis[4-(2-methoxycarbonylphenyl) butyl][2.2]paracyclophane ; Stereochemistry ; 1H/13C inversely correlated NMR ; Bridge proton coupling constants ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The relative orientation of substituents in the opposite rings of one of the isomeric 4,7-Dichloro-5,8,12,15-tetramethoxy-13,6-bis[4-(2-methoxycarbonylphenyl) butyl][2.2]paracyclophanes was determined by establishing by NOE their orientation relative to the bridge protons, which thus served as ‘space-spy nuclei’. The mutual orientation of these bridge protons was ascertained by the analysis of their coupling constants, obtained from a phasesensitive COSY spectrum. The 1H and 13C resonances were assigned with the aid of 1H COSY and 1H/13C inversely correlated spectra.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/mrc.1260261006
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  • 4
    Digitale Medien
    Digitale Medien
    “Proton Sponges” and the Geometry of Hydrogen Bonds: Aromatic Nitrogen Bases with Exceptional BasicitiesNew “Proton Sponge” Compounds, Part 5. - Part 4: [1]. (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 27 (1988), S. 865-879 
    Details
    ISSN: 0570-0833
    Schlagwort(e): Proton sponges ; Hydrogen bonds ; Amines ; Basicity ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Certain aromatic diamines (the “proton sponges”) are found to have exceptionally high basicity constants: this is due to spatial interaction of the basic centers, which are in close proximity. The two factors which are most important in causing this effect are, on the one hand, the extreme steric strain in these systems and the destabilizing effect of the overlap of the nitrogen lone pairs of the neutral diamines and, on the other, the strong NċHċN hydrogen bonds which are formed on monoprotonation and which lead to a considerable relaxation of the steric strain. By the systematic variation of the structures of such aromatic diamines we have been able to study these effects as a function of steric factors, in particular of the geometry and the bond length of the NċHċN hydrogen bonds, by means of X-ray structural analysis. The hydrophobic shielding of the basic centers and the NċHċN hydrogen bonds, which was characteristic of the “proton sponge” compounds studied previously, is indeed responsible for the extremely low rate of protonation and deprotonation of these compounds; however, it apparently has no influence on their high thermodynamic basicity. The recent synthesis and basicity determination of a new type of “proton sponge” with no hydrophobic shielding whatever show that not only very strong but also kinetically active bases are accessible using the “proton sponge” concept. Their unusual properties, which are discussed here as the result of steric interactions between two basic centers, provide examples of the fact that cooperative steric interactions of reactive structural elements can lead to properties which cannot be derived from an isolated consideration of the various functional groups. Such “proximity effects” are certainly of general importance in chemistry and biochemistry; the study of their structure-function relationships is worthy of closer consideration.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/anie.198808653
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