Gas-phase fragmentations of anions derived from N-phenyl benzenesulfonamides.

In addition to the well-known SO2 loss, there are several additional fragmentation pathways that gas-phase anions derived from N-phenyl benzenesulfonamides and its derivatives undergo upon collisional activation. For example, N-phenyl benzenesulfonamide fragments to form an anilide anion (m/z 92) by a mechanism in which a hydrogen atom from the ortho position of the benzenesulfonamide moiety is specifically transferred to the charge center. Moreover, after the initial SO2 elimination, the product ion formed undergoes primarily, an inter-annular H2 loss to form a carbazolide anion (m/z 166) because the competing intra-annular H2 loss is significantly less energetically favorable. Results from tandem mass spectrometric experiments conducted with deuterium-labeled compounds confirmed that the inter-ring mechanism is the preferred pathway. Furthermore, N-phenyl benzenesulfonamide and its derivatives also undergo a phenyl radical loss to form a radical ion with a mass-to-charge ratio of 155, which is in violation of the so-called "even-electron rule."