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

Abstract

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.