OXYGEN-ATOM TRANSFER TO POSITIVE-IONS - A NOVEL REACTION OF OZONE IN THE GAS-PHASE

In the gas phase, neutral ozone (O-3) transfers an oxygen atom to seve ral positive ions, i.e. the radical cations of pyridines (R-Py+.; R = H, CH3, C2H5, and Cl), pyrimidine (Pi(+).), and alkyl halides (CH3X+.; X = Cl and I), and the halogen cations (X+; X = Cl, Br, and I). React ivity changes drastically within the halogen series (Cl+ much less tha n Br+ less than or equal to I+), whereas no O-transfer occurs to F+. T he oxide derivatives R-Py+-O ., Pi(+)-O ., CH3X+-O ., and XO+ are form ed, as demonstrated by pentaquadrupole (QqQqQ) double- and triple-stag e mass spectrometry. No oxygen atom transfer occurs, however, in ''inv erse'' reactions, i.e., those of ionized ozone (O-3(+).) with the corr esponding neutrals; and charge transfer dominates. Ab initio calculati ons suggest that O-transfer from ozone to ionized pyridine yields ioni zed pyridine N-oxide via simple nucleophilic addition of ozone as oppo sed to 1,3-dipolar cycloaddition. Similar nucleophilic addition follow ed by Oz loss is also the most likely mechanism for O-transfer from oz one to the ionized alkyl halides and halogen cations. This novel O-tra nsfer reaction to positive ions, which expands our knowledge of the ri ch chemistry of ozone, introduces a new pathway for the gas-phase oxid ation of halogen atoms, pyridines, pyrimidines, alkyl halides, and ana logues, and consequently for the gas-phase generation of their chemica lly interesting but difficult to access ionized oxides.