Gas‐phase bimolecular chemistry of isomeric cyclic ethylenehalonium and α‐haloethyl cations

The gas‐phase bimolecular chemistry of C 2 H 4 X + (X = F, Cl, Br) cations was studied using Fourier transform ion cyclotron resonance mass spectrometry (FT‐ICR‐MS). The results support earlier suggestions that at least two isomers of the halonium ions C 2 H 4 X + (X = Cl, Br) exist, but no experimental evidence was found for the possibility of more than one stable isomer for C 2 H 4 F + . It is shown that the cyclic ethylenehalonium and α‐haloethyl cations react differently with various substrates. The probe reactions used to characterize the two isomers were hydrogen–deuterium exchange with deuterium oxide and reactions with benzene, alkenes and vinyl ethers. It was found that the α‐haloethyl cations react as proton donors and/or electrophiles, whereas the cyclic ethylene‐chloronium and ethylenebromonium ions react as electrophile and/or as haloganyl cation donors in reactions with alkenes and vinyl ethers.