Prediction of proton affinities and preferred protonation sites in benzene derivatives, from 1s orbital energies

Abstract

We have found a good linear correlation between the experimental·proton affinity and the ‘ab initio’ highest C_1s orbital energy, obtained using an STO–3G minimal basis set, for a wide set of benzene derivatives that are protonated on the ring. Similar relationships were found with the O_1s or the N_1s orbital energies for those compounds that are oxygen- or nitrogen-bases, respectively. This provides a simple method for the calculation of proton affinities and the classification of different centres according to their intrinsic basicity. A possible extension of this treatment to non-aromatic compounds is also discussed.