COMBINED ABINITIO MO AND EXPERIMENTAL STUDIES ON THE UNIMOLECULAR HF LOSS FROM PROTONATED FLUOROBENZENE IN THE GAS-PHASE

The unimolecular loss of hydrogen fluoride from protonated fluorobenzene was studied by chemical ionization mass spectrometry and MP2/6-31G* ab initio MO calculations. Kinetic energy release measurements point to the existence of throe distinct pathways. In addition to direct HF loss from the fluorine-protonated molecule, the calculations reveal the coexistence of 1,1- and 1,2-elimination processes, both derived from ring-protonated isomers. The structures and energetics of the relevant minima and transition structures have been determined, and the combined experimental/theoretical findings point to a unique situation in which protonation of the same precursor molecule by different Bronsted acids affords identical products via three different reaction channels.