Reactions of doubly ionized benzene with nitrogen and water: a nitrogen-mediated entry into superacid chemistry.

Even in the highly diluted gas phase, rather than electron transfer the benzene dication C(6)H(6)(2+) undergoes association with dinitrogen to form a transient C(6)H(6)N(2)(2+) dication which is best described as a ring-protonated phenyl diazonium ion. Isotopic labeling studies, photoionization experiments using synchrotron radiation, and quantum chemical computations fully support the formation of protonated diazonium, which is in turn a prototype species of superacidic chemistry in solution. Additionally, reactions of C(6)H(6)(2+) with background water involve the transient formation of diprotonated phenol and, among other things, afford a long-lived C(6)H(6)OH(2)(2+) dication, which is attributed to the hydration product of Hogeveen's elusive pyramidal structure of C(6)H(6)(2+), as the global minimum of doubly ionized benzene. Nitrogen is essential for the formation of the C(6)H(6)OH(2)(2+) dication in that it mediates the formation of the water adduct, while the bimolecular encounter of the C(6)H(6)(2+) dication with water only leads to (dissociative) electron transfer.