二甲基氯鎓离子(CH_3Cl^+CH_3)及其复合物的理论研究

Theoretic study on dimethyl chloronium ion (CH_3Cl～+CH_3) and its complex

在MP2/6-311+g**水平上优化了(CH3)2Cl+的几何构型,得到的构型参数与实验吻合得很好.相同理论水平下对该阳离子的异构化机理进行了探讨,该反应的决速步需翻越250.6kJ·mol-1的势垒,在C-Cl键断裂及H迁移的协同作用下,可生成质子化的氯乙烷(CH3CH2ClH)+,如有其他阴离子存在,可失去一个质子而转变为氯乙烷.另外,利用自然键轨道理论(NBO)对鎓离子(CH3)2Cl+和碳硼烷阴离子(CHB11Cl11)-相互作用的本质进行了详细探讨,阴阳离子之间的二级稳定化能表明,阴离子上的Cl原子孤对电子与鎓离子上C-H反键相互作用较大,拉长了鎓离子上非平面的C-H键.阴阳离子的静电势图进一步证实负静电势主要分布在氯代碳硼烷上,正电势主要分布在二甲基氯鎓离子上.在B3LYP/6-31G的水平上计算了甲基正离子在鎓离子和碳硼烷阴离子上的迁移机理,迁移过程只需克服11.3kJ·mol-1能垒即可,说明当碳硼烷阴离子存在时,二甲基氯鎓离子不可能发生异构化反应得到氯乙烷,只能产生氯仿.

The geometry of dimethyl chloronium ion （（CH3）2Cl＋） was optimized at the MP2/6-311＋g level,and the structural parameters are in good agreement with experiment.The reaction mechanism about isomerization of （CH3）2Cl＋ was also computed and discussed,the result indicated that the activation energy of the rate-determining step in this reaction is 250.6 kJ mol-1,protonated chloroethane （CH3CH2ClH）＋ can be obtained by the synergistic effect of C—Cl bond breakage and H migration,and （CH3CH2ClH）＋ may lose a proton and produce chloroethane when there exist other anions.In addition,the natural bond orbital （NBO） method was used to deeply analyze the interaction between （CH3）2Cl＋ and carborane （CHB11Cl11）-moieties.The stabilization interaction energies between the cation and anion showed that the lone electron pair,which spreads on the chlorine atom attaching to the carborane anion,strongly reacts on anti-bonding C—H of the chloronium ion,consequently the non-planar C—H bond on the onium ion is elongated.The electrostatic potential map confirmed the negative charge distributed on chlorinated carborane and the positive charge on the onium ion.At last the migration mechanism of methyl cation,which transfers from the chloronium ion to the carborane anion,was calculated at B3LYP/6-31G level.The involved potential barrier was only 11.3 kJ mol-1.This indicated it is impossible that dimethyl chloronium ion turned into chloroethane when carborane anion was present,and it can only produce chloroform.