草酰氯一价正离子构象及其碳—碳键反应活性的理论研究

Theoretical Study on the Conformers and the C—C Bond Reaction Activity of Oxalyl Chloride Cation

用密度泛函方法BHandHLYP在 6 3 11+G(d)和 6 3 11+G(2df)水平上对草酰氯的一价正离子 [(ClCO) + 2 ]作了构象分析 .结果表明 ,(ClCO) + 2 具有平面反式和交叉式两种稳定构象 .交叉构象存在超共轭现象 .此外 ,对草酰氯离子、中性分子各解离通道初级反应的Gibbs自由能的计算 ,发现草酰氯离子C—C键解离通道的反应活性大于中性分子 .对该通道进一步做了反应机理研究 ,证实了热力学结论 ,并且与实验相一致 .

The conformers of oxalyl chloride [(ClCO)(2)] have been extensively studied both theoretically and experimentally while the structure of its cation [(ClCO)(2)(+)] has received less attention. On the other hand, the theoretical study on the single molecule dissociation of oxalyl chloride cation is a whole new aspect. In the present work, the conformers of oxalyl chloride cation was studied at the BHandHLYP level with 6-311 + G(d) and 6-311 + G(2df) basis sets. It is found that (ClCO)(2)(+) have gauche and trans conformers. The orbital interactions in the gauche conformer make it possible to stabilize itself. The C-C bonds in both of the conformers are longer than that in the oxalyl chloride neutral molecule, which suggests in advance that C-C bond in (ClCO)(2)(+) can have some different properties from that in (ClCO)(2). According to the reaction Gibbs free energy calculated at the BHandHLYP/6-311 + G(2df) level, the dissociation of C-C bond in (ClCO)(2)(+) is easier than that in (ClCO)(2). The reaction mechanism confirms this thermodynamic conclusion which is in accord with the experimental results. The frequencies of all the vibrant modes in (ClCO)(2)(+) and the coupling constants between the C-C bond vibrancy and other vibrant modes are also studied. The results indicate that (ClCO)(2)(+) bears bond selectivity in C-C bond dissociation. It suggests that it is possible to excite the vibrancy of C-C bond to a high level with selected laser light, and so that C-C bond can break down at this level.