Captodative effect

Resonance contributors of the 2-(dimethylamino)propanenitrile free radical, adapted from Anslyn[1]

The captodative effect is the stabilization of radicals by a synergistic effect of an electron-withdrawing substituent and an electron-donating substituent.[2][3] The name originates as the electron-withdrawing group (EWG) is sometimes called the "captor" group, whilst the electron-donating group (EDG) is the "dative" substituent.[3] Olefins with this substituent pattern are sometime described as captodative.[2] Radical reactions play an integral role in several chemical reactions and are also important to the field of polymer science.[4]

When EDGs and EWGs are near the radical center, the stability of the radical center increases.[1] The substituents can kinetically stabilize radical centers by preventing molecules and other radical centers from reacting with the center.[3] The substituents thermodynamically stabilize the center by delocalizing the radical ion via resonance.[1][3] These stabilization mechanisms lead to an enhanced rate for free-radical reactions.[5] In the figure at right, the radical is delocalized between the captor nitrile (-CN), and the dative secondary amine (-N(CH3)2), thus stabilizing the radical center.[3]

  1. ^ a b c Anslyn, E. V.; Dougherty, D. A. (2006). Modern Physical Organic Chemistry (Dodr. ed.). Sausalito, CA: University Science Books. ISBN 9781891389313.
  2. ^ a b Concise Dictionary of Chemistry. V&S Publishers. 2012. p. 51. ISBN 9789381588628.
  3. ^ a b c d e Viehe, H. G.; Janousek, Z.; Merényi, R.; Stella, L. (1985). "The Captodative Effect". Accounts of Chemical Research. 18 (5): 148–154. doi:10.1021/ar00113a004.
  4. ^ Cite error: The named reference Tanaka was invoked but never defined (see the help page).
  5. ^ Sustmann, R.; Korth, H.-G. (1990). Advances in Physical Organic Chemistry. San Diego, CA: Academic Press. pp. 131–172. ISBN 0120335263.