Theoretical Investigations Of Reactions Between Methanol And Several Free Radicals

The reactions between methanol and free radicals play an important role in the atmosphere,combustion and interstellar environment.The determination of the reliable potential energy surface plays an important role in the theoretical and experimental study of these reactions.In this paper,the multi-channel hydrogen extraction reaction and nucleophilic-like substitution reactions of CH₃OH+X（X=H,F,Cl,OH）were systematically studied by theoretical and computational chemistry.Specifically,the molecular structure,frequency and energy of this series of reactions were calculated by using various density functional theory methods（DFT）.The reliable potential energy surfaces of methanol and four free radicals were obtained by using the coupling cluster theory and compared with the DFT calculated results.For the CH₃OH+OH systems,multiple density functional theories and coupling cluster methods were used to optimize the structure and analyze the frequency of the stationary points.On the potential energy surface of the hydrogen abstraction reaction path,we found a reaction intermediate complex with a binding energy of-3.56kcal·mol^-1.The energy of the transition state TS1,TS2 are both in good agreement with the benchmark values from literature.In the nucleophilic-like substitution reaction,the reaction barrier of the hydroxyl group attacking the carbon atom is lower than that of the hydroxyl group attacking the oxygen atom.For the CH₃OH+Cl system,we studied the reaction system at the CCSD（T）-F12a/AVTZ level,and obtained the potential energy surface diagrams of two hydrogen extraction reaction paths and four nucleophilic-like substitution reaction paths.The hydrogen abstraction reaction from the methyl group is exothermic.Through intrinsic reaction coordinate（IRC）calculation of the transition state TS2,a new transition state in the formation of hydroxymethyl channel was found,whose energy is7.91 kcal·mol^-1 lower than the reactant asymptote.For CH₃OH+F/H systems,nucleophilic-like substitution reaction paths were calculated at 6-311+G（3df,2p）base group using density functional B3LYP and M05-2X methods and at high levels of CCSD（T）-F12a/AVTZ,CCSD（T）-F12a/AVDZ methods.It is found that the nucleophilic-like substitution reactions of methanol and hydrogen radical are exothermic.For the reaction of methanol and the fluorine radical,the nucleophilic substitution reaction on oxygen is endothermic,while the nucleophilic-like substitution reaction on carbon is exothermic.