A COMPARISON OF THE REACTIONS OF THE OXIDE RADICAL-ANION (O-.) WITH SIMPLE AROMATIC-COMPOUNDS AT ATMOSPHERIC AND AT REDUCED PRESSURE CONDITIONS

The reactions of oxide radical anions (O-.) with benzene and toluene u nder atmospheric pressure (APCI) and conventional chemical ionization (CI) conditions were compared. Hydrogen radical (H.) displacement by o xygen, yielding [M - H + O]-, was observed in both the APCI and the CI source. However, the product, [M - 2H]-., derived from dihydrogen rad ical ion (H-2+.) transfer which was observed in the CI spectra, was co nsistently absent under APCI conditions. This behavior is rationalized in terms of the higher pressures and chemical equilibrium associated with the APCI source. In addition to the formation of the a priori exp ected phenoxide isomers, the reaction of O-. with toluene to yield the [M - H + 0]- product generates a benzyloxide anion. Tandem mass spect rometry data from collision-induced dissociation and isotopic labeling with deuterium support a reaction mechanism initiated by a hydrogen a bstraction for both the H. and the H-2+. transfer pathways.