Comparison of the Addition of CH₃∗ CH₂OH∗, and CH₂CN∗ Radicals to Substituted Alkenes: A Theoretical Study of the Reaction Mechanism

High-level ab initio calculations at the QCISD/6-311G∗∗ + ZPVE level have been carried out to study the addition reactions of CH₃∗, CH₂OH∗, and CH₂CN∗ radicals to the substituted alkenes CH₂=CHX (X = H, NH₂, F, CI, CHO, and CN) and the results analyzed with the aid of the curve-crossing model. We find that the reactivity of CH₃∗ is primarily governed by enthalpy effects, whereas both enthalpy and polar effects are important for the reactions of CH₂OH∗ and CH₂CN∗ There is no general barrier height-enthalpy correlation for the latter two radicals because of the presence in some cases of polar effects that stabilize the transition states without a corresponding stabilization of the products. The polar effects are not sufficient, however, to significantly shift the location of the transition states, so a general structure-enthalpy correlation is observed.