Selected ion flow tube studies of the reactions of H 3O +, NO +, and O 2+ with several aromatic and aliphatic monosubstituted halocarbons

Abstract

We describe the results of a selected ion flow tube (SIFT) study of the reactions of H 3O +, NO +, and O 2 + with the monosubstituted halobenzenes, C 6H 5X, the monosubstituted halotoluene isomers 2-C 6H 5CH 3X and 4-C 6H 5CH 3X (X = F, Cl, Br, I), benzyl chloride, C 6H 5CH 2Cl, benzyl bromide, C 6H 5CH 2Br, and the monosubstituted halomethanes and haloethanes CH 3X and C 2H 5X (X = Cl, Br, I). The H 3O + 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 H 3O + reactions with the aliphatic halocarbons are more varied in their rates and products, and in some reactions association occurs forming H 3O + · 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.