Ab initio quantum mechanical investigation of the reaction mechanisms for the formation of C7H(7)(+) from o-, m-, and p-chlorotoluene radical cations

Abstract

The reaction pathways to C7H(7)(+)(tolyl, benzyl, and tropylium) from o-, m-, and p-chlorotoluene radical cations have been studied at the SCF level of theory using the DZ and DZP basis sets. The equilibrium structures and relative energies for the local minima and transition states have been fully optimized and the harmonic vibrational frequencies have been evaluated to differentiate the local minimum and the transition state. The lowest barrier rearrangement pathway is the formation of the benzyl cation for all three isomers, corroborating the recent experimental findings of Kim and Shin. This benzyl channel involves [1,3] alpha-hydrogen migration at the entrance and the activation energy is calculated to be 40.3, 39.7, and 42.2 kcal mol(-1) for the o-, m-, and p-isomer, respectively. The other competing rearrangement pathway involves [1,2] alpha-hydrogen migration at the entrance, which leads to the tropylium ion, and the activation barrier is predicted to be 55.5, 54.2, and 56.62 kcal mol(-1) for the o-, m-, and p-isomer, respectively. The highest barrier process involves direct C-Cl bond cleavage that yields the tolyl cation with a 0 K dissociation energy of 61.6, 64.6, and 68.92 kcal mol(-1) for the o-, m-, and p-isomer, respectively.