Resonance captodative effect

It has been postulated that the stability of free radicals is enhanced by the presence at the radical center of both an electron-donating and an electron-with-drawing group.This is called the push-pull or captodative effect (see also pp. 159). The effect arises from increased resonance, for example ... 

There are several factors contributing to the stability of radicals. Those are hypierconjugation, resonance, hybridization, captodative effect, and steric effect [24]. Among them resonance and steric effect are important in aryl aminyl radical cations. These aminyl radical cations can be reactive and there are many possible reactions such as fragmentation, dimerization. 

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