Electron-impact studies. XCIX—negative ion mass spectrometry of the o-NO2?C6H4?X?C6H5 systems. Aryl hydrogen scrambling and proximity effects

We report the first example of aryl hydrogen scrambling occurring in a molecular anion prior to or accompanying fragmentation, i.e. for the reaction M]^?· → M ? H₂NO₂.]^? from o-NO₂? C₆H₄? X? C₆H₅ (X = O or S). Proximity effects occur in these spectra when X = CO, NH, O, or S, and certain of these have been substantiated by ²H and ¹⁸O labelling.