Electron impact studies. Part VIII. Mass spectra of substituted azobenzenes; aryl migration on electron impact

Abstract

The spectra of thirty-eight substituted azobenzenes are reported and discussed. The molecular ions are observed as pronounced peaks throughout, and the fragmentation processes are substantiated by exact mass measurements and by the presence of appropriate metastable ions. An approximately linear relationship is shown to exist between the relative ease of cleavage of C–N bonds in 3- and 4-monosubstituted azobenzenes and Hammett σ-values for those substituents, suggestive of some correlation between this mass-spectrometric process and ground-state chemistry. Without exception, the mass spectra of azobenzenes show the presence of skeletal rearrangement ions due to biphenylene, or substituted biphenylene radical ions.