Density Functional Theory Studies on the t-Butoxyl Radical Mediated Hydrogen Atom Transfer Reactions

The reaction mechanisms of hydrogen abstractions from carbon by the t-butoxyl radical were investigated with several density functional theory(DFT) methods, such as CAM-B3LYP, M062x and wB97x. The results show that most of these reactions are dominated more by entropic than by enthalpic factor. The activation free energy barriers were calculated with both gas-phase translational entropy and solution translational entropy, in which those from ideal gas-phase translational entropy(output of Gaussian job) were much higher than the experimental estimations. It has been verified that free-energy barriers of amines and hydrocarbons reactions generated from solution translational entropies are close to the experimental measurements, but all these methods predict a little low free-energy barriers for alcohols and ethers reactions.