Formation and Structural Discrimination of Stable Halophenylium Ions in the Gas Phase.

Fourier-transform ion cyclotron resonance mass spectrometry has been used to identify and characterize the three isomers of X-phenylium ions (X = Cl, Br), through their reactivity features towards CH3Y (Y = Cl, Br). Pure ortho-, meta-, and para-X-phenylium ions (X = Cl, Br) have been independently generated in the source of the instrument by CF3+-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 CH3Y yielding excited adducts which undergo extensive fragmentation by releasing a hydrogen halide mol., a Me halide, a halogen atom, or a Me radical. Competition among these fragmentation pathways depends upon the nature of X and Y and the specific X-phenylium isomer.