Aniline radical cations and anilino radicals

The following is an excellent example where a special technique, in this case time-resolved resonance Raman spectroscopy added significant information which simple optical absorption measurements could not provide. The system of interest is aniline and its radicals generated upon oxidation (e.g., by N3 ). The latter are the radical cation and its deprotonated form existing in equilibrium 12 with a pK of 7.04.29 

One of the informative results obtained is the high C—N stretching mode frequency (1494 cm l) in the radical cation, quite in contrast to the much lower frequency of the same bond in A] ground state aniline (1274 cm- ). The C-N bond in the radical cation thus has assumed a strong double bond character which, by comparison with other systems such as p-phenylene-diamine radical cations, exceeds the value of 1.5 in bond order. This finding implies the radical cation to be mainly C-centered rather than N-centered which is, in fact, corroborated by the observed major termination product of 

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