Gas-phase electrophilic fluorination of methanol by XeF+. Formation and characterization of protonated methyl hypofluorite and hypoxenite

The reactivity of XeF+ ions towards methanol was investigated in the gas ph ase by a combination of mass spectrometric techniques and theoretical metho ds. The charged reagent, generated from the chemical ionization of xenon di fluoride, undergoes both fluorine and xenon transfer to methanol, following dissociation of primary (CH3OH)XeF+ electrostatic adducts. Structural anal ysis performed by low-energy collisionally activated dissociation and react ivity probing techniques, and the results of calculations carried out up to the B3LYP/CCSD(T) level of theory, concur in suggesting the formation of t wo different primary adducts of O-Xe-F and O-F-Xe connectivity that evolve into CH3O(H)Xe+ and CH3O(H)F+, upon loss of F and Xe, respectively. Evidenc e was obtained for the structure of the fluorinated species, identified as O-protonated methyl hypofluorite. This finding allowed the first experiment al evaluation of the proton affinity of CH3OF, which falls in the range 648 .0-680.5 kJ mol(-1), not inconsistent with the 644.8 kJ mol(-1) value calcu lated at the CCSD(T) level and 298 K. The proton affinity of methyl hypoxen ite, CH3OXe, was theoretically calculated to amount to 747.7 kJ mol(-1). Co pyright (C) 2001 John Wiley & Sons, Ltd.