Hydrogen and halogen rearrangements in imidazoles: Hydrogen, fluorine, chlorine and bromine shifts

The structures and energetics of the minima and the transition states corresponding to the migration of hydrogen and halogen atoms (F, Cl, Br) in imidazole and in cyclopentadiene rings have been calculated using the composite method Gaussian-4 (G4), a quantum chemical method for the calculation of energies of molecular species containing first-row, second-row, and third row main group atoms. The heats of formation obtained from the G4 values were found to be reliable by comparing them with the NIST Chemistry WebBook values of cyclopentadiene, imidazole and related compounds. The new G4 values thus obtained have been discussed using correlation analyses. In summary, this work was carried out because there is no clear evidence for intramolecular halogen migrations in azoles.