[Alexander]

I can't understand what is "persistent radical effect"
can somebody explain it?

[mir]

Persistent radicals are radicals with long halftimes, like the molecule TEMPO. Certain radicals are actually unstable, but are kinetically inert because of sterical reasons. Others are specially stabilized by functional groups or through resonance is smeared out throughout the skeleton.

Could you explain where you found this term in use? I will look up in my radical chemistry book as soon as I go working tomorrow :-)