The reactivity of organoboranes in radical substitution reactions

The parameters characterizing substitution reactions of the types R-. + BR3, RO. + BR3, ROO. + BR3, and RS. + BR3 were calculated from the experimental data using the parabolic model of bimolecular radical reaction. Along with the enthalpy of the reaction, the following factors affect the activation energy: triplet repulsion in the transition state, difference ill electronegativities of the atoms forming the reaction center, pi -bonds in the a-position to the reaction center, steric hindrances, and force constants of the reacting bonds. The change in the dissociation energy of the B-C bond in organoboranes, in which alkyl substituents were replaced by alkoxyl and thiyl substituents, was estimated from the kinetic data. The parameters obtained make it possible to calculate the activation energies of individual reactions Of four types under study.