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  • Analytical Chemistry and Spectroscopy  (5)
  • 1995-1999  (5)
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Keywords
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Year
  • 1
    Electronic Resource
    Electronic Resource
    L x-ray fluorescence cross-sections in the atomic region 62 ≤ Z ≤ 70 excited by 15.20, 17.80, 23.62 and 24.68 keV photons (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    X-Ray Spectrometry 24 (1995), S. 244-248 
    Details
    ISSN: 0049-8246
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: L x-ray fluorescence cross-sections were measured for the elements Sm, Ho and Yb using photon energies of 15.20, 17.80, 23.62 and 24.68 keV. Measurements were performed using an x-ray tube with a modified exciter system as the excitation source. In order to improve the efficiency of the detection system, the excitation source, the sample and the detector assembly were placed in a vacuum chamber and a pressure of 10-2 mbar was maintained through-out the measurements. The present system considerably reduced the scattering and background effects and improved the monochromaticity. The x-ray transitions were chosen on the basis of experimentally observed spectra and a particular goup of x-rays are included in the calculation of fractional x-ray emission rates. The experimental results were in excellent agreement with theoretical values.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/xrs.1300240506
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  • 2
    Electronic Resource
    Electronic Resource
    Cycloreversal reaction and ortho interactions in 2-aryl-4H-3, 1-benzoxazin-4-ones on electron impact (1995)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 30 (1995), S. 1195-1200 
    Details
    ISSN: 1076-5174
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A cycloreversal reaction, leading to aroyl cations, is the major process in 2-aryl-4H-3,1-benzoxazin-4-ones under electron impact conditions. The ortho interaction of the methoxy and the nitro groups in the 2-phenyl moieties in these compounds present the most abundant ions at m/z 119 and 134, respectively, in their mass spectra as a result of the transfer of a hydrogen atom from the former and an oxygen atom from the latter to the imine nitrogen of the heterocycle. The ion structures and the mechanisms for the proposed fragmentations are based on high-resolution data, B/E and B2/E linked-scan spectra, collision-activated decomposition-B-/E linked-scan spectra and deuterium labelling.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jms.1190300818
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  • 3
    Electronic Resource
    Electronic Resource
    Dual ortho interaction in 2-substituted-3-(2-methylphenyl)-4(3H)-quinazolinones and their thio analogues under electron impact conditionsDedicated to Professor C. N. Pillai, Department of Chemistry, Indian Institute of Technology, Madras, on the occasion of his 60th birthday. (1995)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 30 (1995), S. 262-268 
    Details
    ISSN: 1076-5174
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Competing ortho interactions, involving the C=X and the ortho-methyl substituent on the 3-phenyl moiety, resulting in the eliminations of ·CH3 and ·OH/·SH from the molecular ions of 2-substituted-3-(2-methylphenyl)-4(3H)-quinazolinones and their thio analogues, were observed. An intramolecular aromatic substitution of the heteroatom of C=X at the ortho-carbon of the 3-phenyl moiety ejecting the methyl group and a hydrogen transfer from the same ortho-methyl substituent to the heteroatom of C=X resulting in the expulsion of ·XH are envisaged for the dual ortho interaction. Another expected fragmentation process observed in these compounds is the transfer of the aryl group from the 3-position of the heterocycle to the heteroatom of C=X leading to the elimination of ArX· from the molecular ions. The proposed fragmentation processes and the ion structures are supported by high-resolution data, B/E and B2/E linked-scan spectra, collisionally activated decomposition B/E spectra and deuterium isotopic labelling.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jms.1190300206
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  • 4
    Electronic Resource
    Electronic Resource
    Intramolecular aromatic substitution and amino-Claisen rearrangement in substituted N-(2-propynyl)anilines on electron impact (1995)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 30 (1995), S. 1028-1033 
    Details
    ISSN: 1076-5174
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: N-(2-Propynyl)anilines undergo amino-Claisen rearrangement to a minor extent in the ion source, losing a molecule of HCN under electron impact conditions. However, metastable molecular ions with energies closer to threshold undergo Claisen rearrangement giving rise to more abundant [M - HCN]+· ions in the first field-free region. Loss of a hydrogen from the molecular ion gives rise to the base peak in the mass spectrum of N-(2-propynyl)aniline. The hydrogen that is expelled for the formation of the [M - H]+ ion is observed to be from the amino nitrogen, propargylic carbon and the ortho-carbon of the ring. The last process leads to a cyclic fragment involving intramolecular aromatic substitution. Double oxygen migration from the nitro group to the triple bond, due to the ortho effect, yields an abundant ion at m/z 105 in N-(2-propynyl)-o-nitroaniline. The proposed fragmentation pathways and ion structures are substantiated by high-resolution data, B/E and B2/E linked-scan spectra, collisionally activated dissociation-B/E linked-scan spectra and deuterium isotopic labelling.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jms.1190300713
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  • 5
    Electronic Resource
    Electronic Resource
    Coherent and incoherent scattering of 42.75 and 47.24 keV x-ray photons scattered from Al, Cu, Y, Mo, Au and Pb (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    X-Ray Spectrometry 24 (1995), S. 172-176 
    Details
    ISSN: 0049-8246
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Using nearly monoenergetic unpolarized Kα x-ray photons, measurements were made of the coherent and Compton scattered intensity in the atomic region 13 ≤ Z ≤ 82 at an angle of 90° with a high-resolution Si(Li) detection system. In order to improve the efficiency of the detection system, the excitation source, detector and the sample assembly were placed in a vacuum chamber and a pressure of 10-2 mbar was maintained throughout the measurements. Experimental scattering cross-sections are compared with the normalized integrated cross-sections based on form factor and incoherent scattering functions. Experimental coherent scattering cross-sections are higher than the theoretical values, indicating the resonance behaviour, fine structure effects and oscillation of coherent intensity around the absorption edges. Experimental incoherent scattering cross-sections are lower than the theoretical estimates for heavy elements, indicating the effect of electron binding at low photon energies.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/xrs.1300240406
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