Diphenylnitroxide radical

Diphenylamine (pKa = 23) can be used to determine the amount of strong base sites by measuring the amount of diphenylnitroxide radicals by ESR which are formed from diphenylamine in the presence of oxygen by an action of basic sites. 

Fig. 3.21 Amounts of diphenylnitroxide radicals (9) and COj molecules irreversibly adsorbed at 373 K (O) on Z1O2 pretreated at various temperatures.

A similar case is the catalysis of Gomberg-Bachmann arylations by A,A-diphenyl-hydroxylamine, which was discovered by Cooper and Perkins (1969). As Scheme 8-46 shows, the covalent adduct cation 8.62 first loses a proton. This facilitates the homolytic dissociation, as a stable radical, A/,A-diphenylnitroxide (8.63), is formed. This... 

It was reasoned that perchlorodiphenyl nitroxide radical (PDNO-) might be much more stable than diphenylnitroxide since, not only would the p-position be blocked, but the NO group would be protected by four flanking o-chlorines, much like t-butyl mesityl nitroxide radical (Forrester and Hepburn, 1970) and PDM- reviewed here. 

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