水或甲酸对CH_3F+OH反应的催化作用

Theoretical Study of the Catalytic Effect of Water,Formic Acid on the Reaction of CH_3F+OH

采用量子化学方法和变分过渡态理论研究了水或甲酸催化羟基自由基提取一氟甲烷中氢的反应机理和动力学.在MC-QCISD//MP2/6-311++G(d,p)水平下计算的势能面表明,水催化或甲酸催化作用下的过渡态形成了很强的氢键,该反应过渡态相对能量从裸反应的4.06kcal/mol分别降低到2.09kcal/mol和-0.20kcal/mol.然而,动力学计算却表明水和甲酸催化下的速率常数比裸反应分别要低3个和1个数量级.因此,水和甲酸均不能加速羟基与一氟甲烷的提氢反应.

The reaction mechanisms and kinetics for the important hydrogen abstraction reaction of CHeF by OH radicals assisted by water, formic acid have been investigated theoretically using quantum chemistry methods and variational transition state theory.The potential energy surfaces calculated at the MC-QCISD//MP2/6-311＋＋G（d,p） levels of theory reveal that the relative energies of the transition states catalyzed by H2O and FA are significantly reduced to 2.09 and -0.20 kcal/mol compared with 4.06 kcal/mol of that without catalyst due to the formation of strong hydrogen bonds. However,the kinetics calculations show that the rate constants are smaller by about 3 or 1 orders of magnitude for water, formic acid assisted reactions than that uncatalyzed reaction,respectively.Consequently,neither water nor formic acid can accelerate the title reaction in the atmosphere.