HCHO+X(X=F、Cl、Br)的反应机理

采用CCSD/6-311++G(d,p)//B3LYP/6-311++G(d,p)方法研究了HCHO与卤素原子X(X=F、Cl、Br)的反应机理. 计算结果表明, 卤素原子X(X=F、Cl、Br)主要通过直接提取HCHO中的H原子生成HCO+HX(X=F、Cl、Br). 另外还可以生成稳定的中间体, 中间体再通过卤原子夺氢和氢原子直接解离两个反应通道分别生成HCO+HX(X=F、Cl、Br)和H+XCHO(X=F、Cl、Br). 其中卤原子夺氢通道为主反应通道, HCO和HX(X=F、Cl、Br)为主要的反应产物; 且三个反应的活化能均较低, 说明此类反应很容易进行, 计算结果与实验结果符合很好. 电子密度拓扑分析显示, 在HCHO+X反应通道(b)中出现了T型结构过渡态, 结构过渡态(STS)位于能量过渡态(ETS)之后. 并且按F、Cl、Br的顺序, 结构过渡态出现得越来越晚.

Reaction Mechanisms of HCHO+X(X=F, Cl, Br)

The reactions of HCHO+X (X=F, Cl, Br) were studied at CCSD/6-311++G(d,p)//B3LYP/6-311++G (d,p) level. The computational results show that the reaction channel of halogen atom X (X=F, Cl, Br) which gains H atom of the HCHOto get HCO+HX(X=F, Cl, Br) is the main reaction channel. Except this reaction channel, a stable complex forms firstly, then the complex via two channels to get the products, one is that the halogen atom gains a hydrogen from HCHO to form HCO+HX(X=F, Cl, Br) and the other is that the complex decomposes directly to H and XCHO (X=F, Cl, Br). The first channel is the main channel and the HCO+HX(X=F, Cl, Br) are the main products. Furthermore, because the energy barriers of the three reactions are low, these reactions could occur easily. The topological analysis of electron density shows that there is a T-shape structure transition state (STS) in the channel (b) of HCHO+X reaction, the STS appears later than the energy transition state (ETS). And the STS appears later and later in the sequence of F, Cl, Br.