Molecular orbital considerations on the reactivities of vinyl compounds. I. Radical reactivity

According to the simple LCAO MO method, the π‐electron localization energies on the β‐carbon of several vinyl monomers (Lβ) and on the α‐carbon of monomer radicals (Lα′) were calculated. Comparison of the calculated values of Lβ and Lα′ with the experimental results so far reported for radical reactivity of vinyl compounds showed (1) that a linear relationship holds between Lβ and the logarithm of methyl affinity, (2) that the smaller the value of Lα′ the larger is the chain termination constant, and (3) that Lβ and Lα′ are parallel, respectively, to the values of Q and P in Price‐Alfrey's notation. These points imply that Lβ and Lα′ would be satisfactory indices for the radical reactivities of vinyl monomers and monomer radicals, respectively. It was also suggested that, in radical copolymerization, the localization energy difference between two monomers, as well as the difference in the π‐conjugation energies with attacking radicals in the transition state of the propagation step, would contribute to the determination of the monomer reactivity ratios.