Substituent and H/D randomization in the mass spectra of substituted diphenylacetylenic compounds
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abstract
The mass spectra of several substituted diphenylacetylenes are reported and the [metastable ion]/[daughter ion] ratios for the isomeric chloro and bromodiphenylacetylenes suggested substituent scrambling in their respective molecular ions. The metastable ion data also indicated equilibration of the chloro substituents in a series of isomeric dichlorodiphenylacetylenes. In addition, the fragmentation patterns for the amino and nitrodiphenylacetylenes differed somewhat from most other aromatic amino and nitro compounds. The aminodiphenylacetylenes fragment with expulsion of H 2 CN from the molecular ion and the expulsion of HCN from the [M 1] + ion was only a relatively minor reaction. 4Nitrodiphenylacetylene loses NO from the molecular ion and OH from the [M NO] + , whereas the more familiar loss of OH from the molecular ion was not observed. The mass spectra of several deuterated substituted diphenylacetylenes clearly showed extensive (but not complete) H/D equilibration in the molecular ion or some subsequent decomposition ion. Comparative studies between 4chloro and 4bromo substituted biphenyl, diphenylacetylene and diphenyldiacetylene indicated similar degrees of H/D randomization, and the results showed that the CC group did not inhibit the proton equilibration between the two phenyl groups. Copyright 1973 Heyden & Son Ltd.
