A Test for Synergetic Captodative Radical Stabilization

In contrast to predictions based on the concept of captodative radical stabilization, the rate constants k for the formation of the radicals 2 from 1 increase dramatically in the order 2a < 2b < 2c. This order of reactivity is not only determined by the different stabilization of the radicals 2 by the pair of substituents X/Y, but also by attractive (anomeric effect in la) and repulsive (1c) σ interactions in the ethane derivatives 1 (a, X = Y = CH3O; b, X = CH3O, Y = CN; c, X = Y = CN).