二甲基氯钅翁离子(CH<sub>3</sub>Cl<sup>+</sup>CH<sub>3</sub>)及其复合物的理论研究
摘要
The geometry of dimethyl chloronium ion ((CH<sub>3</sub>)<sub>2</sub>Cl<sup>+</sup>) 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 (CH<sub>3</sub>)<sub>2</sub>Cl<sup>+</sup> 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<sup>–1</sup>, protonated chloroethane (CH<sub>3</sub>CH<sub>2</sub>ClH)<sup>+</sup> can be obtained by the synergistic effect of C—Cl bond breakage and H migration, and (CH<sub>3</sub>CH<sub>2</sub>ClH)<sup>+</sup> 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 (CH<sub>3</sub>)<sub>2</sub>Cl<sup>+</sup> and carborane (CHB<sub>11</sub>Cl<sub>11</sub>)<sup>–</sup> 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<sup>–1</sup>. This indicated it is impossible that dimethyl chloronium ion turned into chloroethane when carborane anion was present, and it can only produce chloroform.