CH_3X(X=F,Cl,Br,I)和nH_2O(n=1,2)反应的ab initio研究

Ab initio Study on Reaction of CH_3X(X = F,Cl,Br,I) and nH_2O(n = 1,2)

应用Gaussian 09程序,在MP2/6-311+G(2d,2p)理论水平下,对CH3F和H2O反应体系的反应机理进行研究,发现2个反应通道,通道1是CH3F和H2O首先形成复合物CH3F·H2O,然后经过过渡态TS(CH3…F…HOH)直接生成产物CH3OH和HF;通道2是CH3F先经过过渡态TS'(H2C…HF+H2O)形成中间产物P1(H2C·OH2+HF),然后经过过渡态TS''(H2C…OH2+HF)生成产物CH3OH和HF。TS、TS'、TS''分别为68.120,88.422,85.215 kcal/mol,TS比TS'约低20 kcal/mol,即通道1为主要反应途径。研究CH3X(X=F,Cl,Br,I)和nH2O(n=1,2)的反应规律性,对Br、I使用Lan12mb赝势基组。结果表明:CH3X与1H2O反应时,CH3F、CH3Cl、CH3Br、CH3I的反应能垒TS分别为66.635,63.384,61.774,56.254 kcal/mol,随着卤原子序数增加,反应能垒降低约3 kcal/mol。CH3X和2H2O反应时,CH3F、CH3Cl、CH3Br、CH3I的反应能垒TS1分别为57.264,54.084,51.389,39.816 kcal/mol;CH3F、CH3Cl、CH3Br的TS1比TS低10 kcal/mol左右,而CH3I的TS1比TS低16.4kcal/mol。CH3F水解的活化能TS1为57 kcal/mol,与实验值吻合较好。

The reaction mechanism of CH3F and H20 was studied at the theoretical level of MP2/6 -311 ＋ G （2d,2p） using Gaussian 09 program. There were two reaction channels. The first one began with the forma- tion of the compound CH3F · H20, and the product of CH3F and H20 was formed through the transition state of TS （ CH3 ...F... HOH）. In the second channel, the intermediate product of P1 （ H2 C · OH2 ＋ HF） was formed through the transition state of TS（ H2 C... HF ＋ H2 O）, then through the transition state of TS＂（ H2 C ...OH2 ＋ HF） to form the final product of CH30H and HF. The energy barrier of TS,TS,TS vere 68. 120, 88. 422,85. 215 kcal/mol respectively. The barriers of TS is 20 keal/mol lower than that of TS＇,which meant that the first channel was the dominant one. MP2/6 -311 ＋ G（2d,2p） method was used to study the reac- tion mechanism of CH3 X （ X = F, C1） and nH20 （ n = 1,2 ） through channel one, and MP2/GEN 6 - 311 ＋ G（2d ,2p）Lan12mb was used for that of C H3 X （X = Br, I） and nil20 （n = 1,2 ）. It shows that the energy bar- tiers are 66. 635,63. 384,61. 774,56. 254 kcal/mol, respectively when CH3X reacts with 1H20, and it de- creased about 3 kcal/mol with the atom number increase of halogen atoms. They are 57. 264,54. 084, 51. 389,39. 816 kcal/mol,respectively when CH3X reacts with 2H20. The energy barrier of TS1 with 2H20 is about 10 kcal/mol lower than TS with 1H20 for CH3F, CH3C1, CH3Br, and it is 16.4 kcal/mol for CH3I. The active energy of CH3F is 57 kcal/mol, which is agree with the experimental data well.