Selected ion flow tube studies of the reactions of H3O+, NO+, and O2+ with several aromatic and aliphatic monosubstituted halocarbons

We describe the results of a selected ion flow tube (SIFT) study of the reactions of H3O+, NO+, and O-2(+) with the monosubstituted halobenzenes, C6H5X, the monosubstituted halotoluene isomers 2-C6H5CH3X and 4-C6H5CH3X (X = F, Cl, Br, I), benzyl chloride, C6H5CH2Cl, benzyl bromide, C6H5CH2Br, and the monosubstituted halomethanes and haloethanes CH3X and C2H5X (X = Cl, Br, I). The H3O+ reactions with the aromatic halocarbons, M, are rapid and mostly proceed via direct proton transfer producing MH+ ions, the exceptions being the benzyl halides in which only HCl (and HBr) elimination occurs from the nascent MH+ ions. The H3O+ reactions with the aliphatic halocarbons are more varied in their rates and products, and in some reactions association occurs forming H3O+. M ions. The NO+ reactions with the aromatics mostly proceed rapidly via charge transfer producing the parent cations M+ only, whereas the NO+ reaction with the aliphatics are generally slow association reactions resulting in NO+. M ions. The O-2(+) reactions are fast mostly proceeding via nondissociative charge transfer producing the parent cations M+ only, but in some of these reactions minority dissociative charge transfer channels are evident in which a halogen atom is eliminated leaving the corresponding hydrocarbon ion. In conclusion, some general observations are made concerning near-thermoneutral charge transfer and proton transfer processes. (Int J Mass Spectrom 189 (1999) 213-223) (C) 1999 Elsevier Science B.V.