The Collision-Induced Dissociations of Deprotonated Amines in the Gas Phase

Abstract

The major collision-induced fragmentations of deprotonated primary and secondary amines are best rationalized as proceeding through the intermediacy of ion complexes. For example, the characteristic fragmentation of deprotonated ethylamine is

MeCH₂NH^- → [Me^-(CH₂=NH)] → CH₂N^- + CH₄

Secondary alkylamines behave in a similar fashion. The occurrence of proton transfer as a prelude to fragmentation is rare: the only example observed in this study is the probable reaction

PhNEt →→ PhNHCHMe → [(PhNH=CH)Me^-] → C₇H₆N^- + CH₄

which is preceded or accompanied by proton transfer between the methylene and phenyl substituents. Deprotonated aniline undergoes specific elimination of CNH from the 1-position to form the cyclopentadienyl anion. Finally, retro reactions are observed for the piperazine anion, e.g.

HN(CH₂CH₂)₂N → -CH₂CH₂N=CH₂+CH₂NH