In addition to computational studies, experimental liquid-phase spectroscopy studies, mainly NMR and IR spectroscopy, were widely used to locate the preferred protonation site (s) of the phenol and benzene molecules substituted as a function of solvent and temperature . To produce information about the competitive protonation in the substituents in substituted aromatic compounds, in addition to the protonation in the ring itself, it is necessary to separate the effects of the solvent from the molecular electronic properties, whose investigations must be made in the gas phase .