O −˙ chemical ionization mass spectra of fluoroaromatic compounds

The O −˙ chemical ionization (CI) mass spectra of the mono‐ to pentafluorobenzenes, fluorotoluenes and fluoroanisoles were measured. For comparison, the O −˙ CI mass spectra of toluene (including deuterium‐labelled variants) and anisole were also measured. The major reaction channels of O −˙ with fluorobenzene involve H‐atom displacement and H   2 +˙abstraction. With increasing fluoring substitution H + abstraction increases in importance. For the tri‐ and tetrafluorobenzenes H   2 +˙˙abstractions is important only when there are two hydrogen ortho to each other. Reaction channels which are unique to the fluoroaromatic molecules involve the formation of [M + O – HF] −˙ , which, for polyfluoro compounds, fragments further by elimination of HF or CO. For the fluoroanisoles, formation of FC 6 H 4 O − and elimination of CH 2 O from [M – H] − and [M – 2H] −˙ are important reaction channels. The formation of [M + O – H] − by reaction of O −. with toluene is shown to involve specific displacement of a ring hydrogen, whereas the formation of [M – H] − involves primarily abstraction of a proton from the methyl group. By contrast, H   2 +˙abstraction is non‐specific and proceeds by three pathways: (i) abstraction of two hydrogens from the aromatic ring, (ii) abstraction of two hydrogens from the methyl group and (iii) abstraction of one hydrogen from each position; however, the resuls are not in accord with a random selection of hydrogens.