Fourier-transform ion cyclotron resonance mass spectrometry has been used t
o identify and characterize the three isomers of X-phenylium ions (X = Cl,
Br), through their reactivity features towards CH3Y (Y = Cl, Br). Pure orth
o-, meta-, and para-X-phenylium ions (X = Cl, Br) have been independently g
enerated in the source of the instrument by CF;-induced F- abstraction from
the corresponding X-fluorobenzenes. Isomeric X-phenylium ions (X = Cl, Br)
attack the Y atom and the C-H bonds of CH,Y yielding excited adducts which
undergo extensive fragmentation by releasing a hydrogen halide molecule, a
methyl halide, a halogen atom, or a methyl radical, Competition among thes
e fragmentation pathways depends upon the nature of X and Y and the specifi
c X-phenylium isomer. (C) 2000 Elsevier Science B.V.