Using the MOLPROJ software, optimized structures of the selected compounds were analyzed using their MOs eigenvectors and overlap matrices, both extracted from output files of single point energy calculations with GAMESS. The degree of localization for each MO and their respective energies were calculated and analyzed. For this, the PG projection operators were applied to all 2px-z orbitals of aromatic carbon atoms as for the hydroxyl oxygen atom. Subsequently, we calculated the coefficients of degree of localization for the HOMO and FERMO molecular orbitals (ΓHOMO and ΓFERMO) for comparison. These coefficients are shown in Table , together with the corresponding MO energies. A: HSO3F/SbF5 ; B: H2SO4 ; C: HSO3F ; D: CF3SO3H From these data, two doubts emerged: (1) is the reaction site pointed by the software in accordance with experimental results found in the literature, based on NMR?