An electron spin resonance study of alkyl radical addition to diethyl vinylphosphonate

Abstract

The irreversible addition of alkyl radicals to diethyl vinylphosphonate to give the α-phosphorylalkyl radicals (1) has been studied by e.s.r. spectroscopy at 233 K in hydrocarbon solvents. The rate constants for addition (k_add) have R·+ H₂CCHP(O)(OEt)₂ [graphic omitted] RCH₂ĊHP(O)(OEt)₂(1) been determined relative to those (2k^A_t) for self-reaction of (1) for a series of addenda. The values of 2k^A_t have been measured in separate kinetic e.s.r. experiments for (1; R = Me)(2.0 × 10⁹ dm³ mol^–1 s^–1) and (1; R = Bu^t)(5.0 × 10⁸ dm³ mol^–1 s^–1) and thus absolute values of k_add were obtained. The rate constant k_add increases along the series R·= Me·(2.5 × 10³ dm³ mol^–1 s^–1) < R^prim· < R^sec· < Bu^t·(5.9 × 10⁴ dm³ mol^–1 s^–1) and this order is interpreted in terms of the over-riding importance of polar effects in determining the size of the barrier for addition of these nucleophilic radicals to the electron deficient alkene.