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

Abstract

AbstractThe reactivity of XeF+ ions towards methanol was investigated in the gas phase by a combination of mass spectrometric techniques and theoretical methods. The charged reagent, generated from the chemical ionization of xenon difluoride, undergoes both fluorine and xenon transfer to methanol, following dissociation of primary (CH3OH)XeF+ electrostatic adducts. Structural analysis performed by low‐energy collisionally activated dissociation and reactivity probing techniques, and the results of calculations carried out up to the B3LYP/CCSD(T) level of theory, concur in suggesting the formation of two 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. Evidence was obtained for the structure of the fluorinated species, identified as O‐protonated methyl hypofluorite. This finding allowed the first experimental 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 calculated at the CCSD(T) level and 298 K. The proton affinity of methyl hypoxenite, CH3OXe, was theoretically calculated to amount to 747.7 kJ mol−1. Copyright © 2001 John Wiley & Sons, Ltd.