COMPARISON OF THE ADDITION OF CH3-CENTER-DOT, CH2OH-CENTER-DOT, AND CH2CN-CENTER-DOT 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, Cl, 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.