Mass spectra of 3-nitro-2H-chromenes and 3-nitrochromans

Abstract

The 4kV, 70 eV electron impact mass spectra (e.i.-m.s.) of eight 2-aryl-3-nitro-2H-chromenes and ten 2-aryl-3-nitrochromans of diverse functionality are reported and discussed. The peak due to the molecular ion is always appreciable and often intense in these spectra. Loss of NO₂ from M⁺˙ is responsible for the base peak in the nitrochromene spectra. In contrast, [M– HNO₂]⁺˙ is more abundant than [M– NO₂]⁺ in the spectra of the nitrochromans; furthermore, this unusual HNO₂ loss persists even for metastable molecular ions. A diagnostically important ion, of nominal structure [ArCH₂]⁺, accounts for the base peak in the chroman spectra; this ion, which defines the formula of the 2-aryl subsituent, corresponds to elimination of benzofuran from [M– NO₂]⁺.

All the compounds studied exhibited [M]^–˙ ions in their electron capture negative ion chemical ionisation (c.i.) spectra. Apart from [M]^–˙ and the base peak at [M– NO₂]^–, few ions were of considerable abundance in these spectra, although [NO₂]^– ions were present in the nitrochroman series.