CH_3CH_nF_(3-n)(n=0,1,2)与HOOO反应机理的DFT研究

Density Functional Theory Studies on the Mechanism of the Reaction of HOOO with CH_3CH_nF_(3-n)(n=0,1,2)

采用密度泛函理论研究了富氧自由基HOOO与CH_3CH_nF_(3-n)(n=0,1,2)的反应机理.用MPW1K和BHandHLYP方法结合6-31+G(d,p)基组优化了反应势能面上各驻点的几何构型,并用内禀反应(IRC)计算和频率分析方法对过渡态进行了验证.对所有的驻点进行了CCSD/6-31+G(df,p)//MPW1K/6-31+G(d,p)的单点能量计算,从而得到了各驻点的零点能校正值(ZPE)和最小能量途径(MEP).结果表明,当HOOO进攻CH_3CH_nF_(3-n)(n=0,1,2)分子的相同基团CH_3上的H原子时,随着氟原子取代数目的增加,反应势垒也随之增加,这个规律也反映出氟原子的取代数目可以影响到端基CH_3基团抽氢反应速度的快慢.而在HOOO+CH_3CH_nF_(3-n)(n=1,2)反应中,HOOO抽端基CH_nF_(3-n)(n=1,2)中的H原子比抽CH_3基团上的H原子反应的速度快,即生成物CH_3CH_(n-1)F_(3-n)(n=1,2)为此反应中的主要产物.

The reaction mechanism of CH_3CH_nF_3-n（n=0,1,2） with HOOO have been studied using the density functional theory （DFT） at the BHandHLYP/6-31 ＋G （d, p） and MPWB1K/6-31 ＋ G （d, p） levels of theory. The geometries for the reactants, the transition states and the products are completely optimized. All the transition states are verified by the vibrational analysis and the instrisic reaction coordinate （IRC） calcula- tions. The energies of all of the stationary points are refined by using CCSD/6-31＋G（df,p） calculations based on the optimized geometries at the MPW1K/6-31＋G（d,p） level of theory, and the zero point energy（ZPE） correction of all stationary points and the minimum energy paths（MEPs） were obtained. The calculated results show that HOOO attacks the same group CH3 of molecules CH_3CH_nF_3-n（n=0,1,2） with the increase of the number of fluorine substitutions, the forward barrier heights increase. This reflects that the fluorine substitu- tion can affect the H-abstraction process. In addition, in the reaction of CH_3CH_nF_3-n（n=0,1,2） with HOOO, the H abstraction by HOOO from CH.Fa .（n= 1,2） group is dominant with the smaller potential barrier. Conse- quently, it could be anticipated that CH_3CH_nF_3-n（n=0,1,2） may be the main product in the reaction of HOOO with CH_3CH_nF_3-n（n=0,1,2） molecules.