Is a thin mechanism appropriate for aromatic nitration?

The mechanism of toluene nitration by NO 2 BF 4 in dichloromethane solution is investigated by performing advanced ab initio MD simulations of the reaction trajectories, including at full quantum mechanical level the effects of both the solvent and of the counterion. The time evolution of the encounter complex, as well as that of the associated electronic structure, for different trajectories reveals that a single electron transfer step fastly occurs after reactants are accommodated in a common solvation shell, always preceding the formation of the σ-complex. The present results strongly suggest that the regioselectivity of the reaction is spin-density driven and that a thin mechanism, one based on reaction intermediates and transition states, can be appropriate to describe aromatic nitration.