Loss of aromaticity and π-electron delocalization in the first step of the electrophilic aromatic nitration of benzene, phenol and benzonitrile

In this paper, a computational study on the first stages of the nitration of benzene, phenol and benzonitrile is presented. It is found that at the B3LYP/6-31G* and B3LYP/6-31+G* levels of theory the σ-complexes associated with these reactions show local diamagnetic effects of much less intensity than the aromaticity associated with ring currents. It is found that these diamagnetic effects are more important in the meta regioisomeric σ-complexes. In the case of phenol, the meta-σ-complex is the less stable one in good agreement with the experimental evidence available. In contrast, our results indicate that the meta-σ-complex corresponding to the nitration of benzonitrile is not the most stable one. This situation does not change at the MP2/6-31+G*+ΔZPVE and G3B3 levels of theory or when solvent effects were included in the calculations.