Theoretical studies of the effects of substituents on the ring opening reactions for the cyclopropylcarbinyl radical

DFT (U)B3LYP/6-31G(d,p), (U)B3LYP/6-31+G(d,p), and (U)B3LYP/6-311+G(d,p) calculations were carried out to investigate the ring opening reactions of the cyclopropylcarbinyl radical (leading to the 3-butenyl radical) and its mono-substituted analogues containing the methyl, ethyl, propyl, isopropyl, isobutyl, fluorine, chlorine, bromine, hydroxyl, methoxy, cyanogen, nitryl, vinyl, and phenyl substituents on the ring (leading to the pseudo-secondary and primary radicals, respectively). The enthalpies of activation, rate constants, and reaction enthalpies for all ring opening reactions were calculated. The predicted enthalpy of activation, rate constant, and reaction enthalpy of the cyclopropylcarbinyl radical ring opening reaction are in excellent agreement with the corresponding experimental values. For the alkyl (methyl, ethyl, propyl, isopropyl, and isobutyl) substitutions, steric effects are found to be the dominating factor to affect the ring opening reactions, while for the rest substitutions, the stereoelectronic effects play the most important roles. Our calculations indicate that the cyanogen, nitryl, vinyl, and phenyl substituents, which contain π bonds, have much larger effects on the ring opening reactions than the other substituents.