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The captodative effect is the stabilization of radicals by a synergistic effect of an electron-withdrawing substituent and an electron-donating substituent. The name originates as the electron-withdrawing group is sometimes called the "captor" group, whilst the electron-donating group is the "dative" substituent. Olefins with this substituent pattern are sometime described as captodative. Radical reactions play an integral role in several chemical reactions and are also important to the field of polymer science.
When EDGs and EWGs are near the radical center, the stability of the radical center increases. The substituents can kinetically stabilize radical centers by preventing molecules and other radical centers from reacting with the center. The substituents thermodynamically stabilize the center by delocalizing the radical ion via resonance. These stabilization mechanisms lead to an enhanced rate for free-radical reactions. In the figure at right, the radical is delocalized between the captor nitrile , and the dative secondary amine 2], thus stabilizing the radical center.