Kinetic–EPR studies of the addition of aliphatic radicals to acrylic acid and related alkenes: the interplay of steric and electronic factors

Abstract

A continuous-flow system approach with EPR detection and steady-state analysis has been employed to determine the rate constants for addition of a range of aliphatic radicals to acrylic acid and related alkenes in aqueous solution at room temperature. For acrylic and methacrylic acids the rate constants (in the range 2 × 10⁵–ca. 10⁸ dm³ mol^–1 s^–1) are governed largely by polar effects in the transition state, though the deviation from planarity of the attacking species may be important for ·CHMeOH and related radicals. As expected, steric effects play a prominent role in causing retardation in the reactions of crotonic and 3,3-dimethylacrylic acids, and in addition of ·CMe₂OH.