Theoretical studies of aromatic substitution. Part II. Gas-phase protonation of benzene and toluene

Abstract

Complete structure determinations for the Wheland intermediates in the electrophilic substitution of benzene and toluene, as well as for the unprotonated species, have been carried out using the MINDO/2′ method. Studies of the potential energy surfaces about these energy minima afforded the frequencies of vibration (in the harmonic approximation), from which were constructed vibrational partition functicns and vibrational contributions to the free energy and enthalpy functions. Thermodynamic functions for the various species are recorded. The results are compared with existing structural and thermodynamic data, and the relationship of the present calculations to the theory of aromatic substitution is discussed.