Rates of the possible cross-disproportionation reactions of these radicals relative to their rates of cross-combination, have been measured and are compared with auto-disproportionation-to-combination ratios which were also determined for these radicals. Selected asymmetric azo alkanes RNNR′ and mixtures of symmetric azo alkanes RNNR were used as sources of the desired free radicals. Photolysis under relatively high intensity conditions (ca. 1018 quanta/cm2 s) at room temperature generated the radicals in sufficiently high concentration that competing reactions of abstraction and condensation were negligible. Both the alkene and alkane products of disproportionation reactions were measured to ensure the completeness of the mechanism invoked and to increase the accuracy of the results. Δ(Me, Et) = 0.036 ± 0.003, Δ(Me, Prn) = 0.058 ± 0.004, Δ(Me, Prs) = 0.163 ± 0.005, Δ(Et, Prn) = 0.065 ± 0.005, Δ(Et, Prs) = 0.18 ± 0.008, Δ(Prn, Et) = 0.057 ± 0.005, Δ(Prs, Et) = 0.12 ± 0.01, and Δ(Prn, Prs) = 0.41 ± 0.02 were deduced from the data, where Δ(A, B) refers to the ratio of disproportionation producing the alkane product derived from A to the combination of A with B.

1,1′-Azoisobutane, 2,2′-azoisobutane, 1-isobutyl azoethane, and mixtures of azoethane with 2,2′-azoisobutane were photolyzed under high intensity conditions in order to study the disproportionation of isobutyl and t-butyl free radicals and their cross reactions with ethyl radicals. The relative rates of disproportionation to combination which were determined for the various radical interactions are as follows: Δ(i-C4H9, i-C4H9), 0.078; Δ(t-C4H9, i-C4H9), 2.32; Δ(C2H5, i-C4H9), 0.04; Δ(C2H5, t-C4H9), 0.498; Δ(i-C4H9,C2H5), 0.04; Δ(t-C4H9, C2H5), 0.283.