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 H2+. abstraction. With increasing fluorine substitution H+ abstraction increases in importance. For the tri- and tetrafluorobenzenes H2+. abstraction is important only when there are two hydrogens 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 FC6H4O- and elimination of CH2O 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.