Stable Radicals of Aromatic Amines

The investigation of the structure of radicals of aromatic amines, produced by their reaction with active radicals of the type of RO and RO2, is of considerable interest. It was shown in [12] that the radicals of secondary aromatic amines obtained in this case represent the corresponding azotoxides. The mechanism of their formation can be represented in the following way  

The spectrum is characterized by a triplet structure with splitting of 10 Oe, related to the magnetic moment of the nucleus Each component of the triplet is subdivided into 15 lines. Their intensity ratio gives evidence that the protons of the benzene rings on which this splitting arises are nonequivalent. 

When phenothiazine interacts with peroxide radicals, radicals of the corresponding azotoxide (XI), the EPR spectrum of which is shown in Fig. 40a, are also formed. 

We can see from the spectrum that the unpaired electron interacts strongly with the four equivalent protons of the benzene rings, which leads to splitting of each component of the triplet into five lines with a distance of 2.3 Oe. These protons are probably ortho- and para-protons, denoted in the formula of the radical by asterisks. However, when the solution of the radicals is further diluted, as the intermolecular interaction is removed, further splitting of the components of the quintiplet on the remaining proton is observed. The value of the splitting is about 0.5 Oe (Fig. 40b). 

This means that the probability that the unpaired ir-electron will be found in the ortho- and para-positions is almost five times as great as the probability that it will be found in the meta-positions. 

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