The interplay between electron transfer and attack on halogen in gas-phase reactions of negative ions with fluoro-chloromethanes and fluoro-bromomethanes

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Abstract The gas-phase reactions of HO − , CH 2 S −· and CH 2 CHCH 2 − with the complete series of fluoro-chloromethanes and fluoro-bromomethanes have been studied with use of Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. The HO − ion is unreactive towards CF 3 Cl, CF 2 Cl 2 , CFCl 3 and CF 3 Br but reacts with CCl 4 by attack on a chlorine atom and with CF 2 Br 2 , CFBr 3 and CBr 4 by attack on a bromine atom. The CH 2 S −· radical anion is also unreactive towards CF 3 Cl, whereas an efficient electron transfer takes place with the other halomethanes. For most of the halomethanes, the electron transfer from CH 2 S −· yields stable molecular radical anions together with X − and CH 2 SX − ions (X  Cl and Br). The allyl anion reacts with nearly all substrates by nucleophilic attack on a chlorine or bromine atom and/or electron transfer. Nucleophilic attack on a chlorine atom is the exclusive reaction of the allyl anion with CF 3 Cl and the most important pathway in the reaction with CF 2 Cl 2 and CFCl 3 . Electron transfer from the allyl anion leads to minor amounts of the radical anions of CF 2 Cl 2 , CF 3 Br and CF 2 Br 2 , whereas only Cl − or Br − ions arise by electron transfer to most of the other halomethanes. The occurrence of electron transfer and/or halogen attack is discussed in terms of the trend in the electron affinities of the substrates and the thermodynamics of the different overall processes.