Collision-induced dissociations of substituted benzyl negative ions in the gas phase. The elimination of C4H4

The major collision-induced dissociations of PhEt2 involve the losses of H˙, H2, and CH4. Loss of H˙ occurs from the phenyl ring, H2 is eliminated principally by the process PhEt2→ PhC(Et)CHCH2–+ H2, while methane is lost by the stepwise process PhEt2→{Me–[Ph(Et)CCH2]}→(C6H4)–C(Et)CH2+ CH4, in which the second step (deprotonation) is rate-determining. The characteristic fragmentation of both Ph2CH– and Ph3C– is loss of C4H4. This loss occurs without atom randomisation and Dewar benzene intermediates are proposed. The ion Ph3C– also loses C6H6; this is a slow process which is preceded or accompanied by both intra- and inter-ring hydrogen scrambling.