Stability of PhCH 2CH 2ĊHX (X = H, CF 3, Me, CO 2Me) Radicals

Using EPR spectroscopy, β-fragmentation of the radicals PhCH 2CH 2ĊHX (R 1, X = H; R 2, X = CF 3; R 3, X = Me; R 4 X = CO 2Me) accompanied by C—C bond cleavage has been found and studied, and the activation energy of this reaction has been calculated, thus permitting us to determine the rate constants for fragmentation of R 1 ( k 3a = 3.9( ± 0.2) × 10 4 s −1, R 2 ( k 3b = 6.5( ± 0.4) × 10 3 s −1 and to evaluate the value of this rate constants for radical R 3 and R 4 ( k 3 = 10 2 s −1) at 22 °C.