Ethylene bromonium and 1-bromoethyl cations and their neutral and anionic counterparts: a tandem mass spectrometry study of dissociations and gas phase redox reactions

Abstract

The unimolecular chemistry of ethylene bromonium cation (cyclo-CH₂CH₂Br⁺, 1⁺) and 1-bromoethyl cation (CH₃CH⁺Br, 2⁺) has been probed by metastable ion (MI) characteristics, collisionally activated dissociation (CAD) and neutral fragment reionization (N_fR). These isomers undergo many common decompositions but can, nevertheless, be distinguished based on the structurally indicative >˙>CH₃vs. CH₂ losses. Neutralization–reionization (NR) experiments have further shown that the gas phase reduction of 1⁺ and 2⁺ leads to 2-bromoethyl (>˙>CH₂CH₂Br, 3) and 1-bromoethyl (CH₃ĊHBr, 2) radicals, respectively, both of which are stable species. However, from the incipient C₂H₄Br^– anions emerging upon charge reversal of 1⁺ and 2⁺, only CH₃CH^–Br (2^–) is found to be a bound anion.