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  • 1
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Four tetrachlorinated bipbenyls were chlorinated with 35Cl2 to yield seventeen polychlorinated biphenyls (PCBs) substituted once or twice with chlorine enriched in 35Cl. Gas chromatographic analysis of the mixtures allowed the identification of the labelled PCBs produced by comparison of their relative retention times with published values. This also permitted the assignment of the position of the labels in these molecules. Mass spectrometric determination of the 35Cl/35Cl ratio of the ions corresponding to successive dechlorination of these PCBs in positive-ion electron impact (EI) allowed quantification of the residual 35Cl label in these ions. Chlorines in the ortho position are lost preferentially to those in meta or para positions. The first dechlorination reaction was found to be totally regioselective for at least two PCB congeners.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electron-capture negative-ion chemical Ionization mass spectra of 36 35Cl mono- and di-labelled penta- and hexachlorobiphenyls were studied. Under the conditions of the analyses, the dechlorination of these congeners probably proceeds through electrophilic hydrogen atom attachment followed by rapid loss of the chlorine atom at the same position. These dechlorination reactions occur regioselectively. When present, ortho-chlorines are lost preferentially to meta- and para-chlorines. The extent of the dechlorination reaction, as seen by the relative abundance of the [MH — Cl]- ions, decreases with increasing number of ortho-chlorines.
    Additional Material: 8 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 30 (1995), S. 885-892 
    ISSN: 1076-5174
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: DDT and several of its metabolites were synthesized with their aromatic chlorines enriched with 37Cl. The mass spectra of these compounds were recorded under electron impact and under methane positive-ion and electroncapture negative-ion chemical ionization. The regioselectivity of the dechlorination reactions was determined by measurement of the relative proportions of the unlabeled aliphatic versus the labeled aromatic chlorines in the various fragment ions observed. For all the α,β-unsaturated compounds studied under electron impact ionization, the regioslectivity is small, as both the aromatic and the aliphatic chlorines are lost. Under positive-ion chemical ionization, the dechlorination is highly regioselective, the aliphatic chlorines being almost exclusively lost. Under electron-capture negative-ion chemical ionization, the regioselectivity is also very high and the reactivity of the various chlorines is often controlled by the position of the aromatic chlorines.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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