CALCULATION OF IONIZATION-POTENTIALS AND C-H BOND-DISSOCIATION ENERGIES OF TOLUENE DERIVATIVES

We present ab-initio and density functional theory calculations (with both local and nonlocal exchange-correlation functionals) on the ioniz ation potentials and C-H bond dissociation energies in para-substitute d toluene derivatives and compare the results with available experimen tal data. We find that with the Hartree-Fock formalism the inclusion o f correlation and spin projection is necessary to achieve satisfactory agreement with experiment. The DFT calculations lead to a good reprod uction of the ionization potentials with all exchange-correlation func tionals investigated, while for the C-H bond energies nonlocal exchang e-correlation functionals are necessary. In all cases the B3LYP functi onal leads to results that are closest to experiment. In agreement wit h experimental data, we find that the ionization potentials are sensit ive to the ring substituents, whereas the bond dissociation energies a re hardly affected. The significance of these findings for the reactio n mechanism of the chloroperoxidase-dependent oxidation of toluene der ivatives is discussed.