Is Electron Transfer a Step in the Nitration of Reactive Aromatics?

Controlled-potential electrolysis of a mixture of NO₂ and naphthalene, at an applied potential capable of oxidizing naphthalene but not NO₂, produces a mixture of nitronaphthalenes. The ratio of 1-nitronaphthalene to 2-nitronaphthalene is 10.2 ± 1, the same as the 10.9 ± 1 produced in the direct nitration of naphthalene with HNO₃ + H₂SO₄. The observation that the same mixture is formed by the two routes is taken as evidence that a radical pair is involved not only in the electrochemical synthesis but also in the direct nitration. This requires that electron transfer from aromatic to NO₂⁺ be sufficiently fast to compete with C-N bond formation. Moreover, formation of a radical pair is presented as the explanation for the high intramolecular selectivity of nitration, contrasting with a lack of intermolecular selectivity. This full paper presents the experimental details of a Communication to the Editor published in JACS in 1977, along with a review of experimental and computational assessments both in favor and in opposition to that Communication.