锗烯X_2Ge(X=H、CH_3、F、Cl、Br)与乙烯环加成反应的量子化学研究

Quantum Chemistry Study on Cycloaddition Reaction of Germylene X_2Ge(X=H,CH_3,F,Cl,Br ) and Ethylene

利用量子化学密度泛函理论的B3LYP方法,在6-311G的水平上,对锗烯X2Ge(X=H、CH3、F、Cl、Br)与C2H4的环加成反应进行了计算研究.结果表明,锗烯的基态是单重态,取代基的电负性越强,单-三态的能量差越大;控制反应的因素是电子效应,而不是立体效应;取代基的电负性越强,反应的活化能越高,放热越少;该反应由两步组成,第一步生成中间配合物,是一个无势垒的放热过程,第二步经过渡态生成产物.

The potential energy surfaces for the cycloaddition reactions of singlet germylene X2Ge(X=H,CH3,F,Cl,Br) and ethylene were studied using density functional theory (DFT) .All the stationary points were determined at the B3LYP/6 311Gtheory level .The reaction paths from the transition states to both the reactants and products direction were examined by using the intrinsic reaction coordinate (IRC) .A configuration mixing model (CMM) was used to explain the barrier height and the reaction enthalpy .The results showed that the ground state of germylene X2Ge is singlet .The more electronegative the substitutes X in X2Ge are,the larger ΔES T of X2Ge will be.It is the electronic factors,rather than the steric factors,that play a decisive role in determining the chemical reactivity of germylene .The reactions are in two steps :(1) germylenes and ethylene form an intermediate complex through an exothermal reaction without any barrier;(2) the intermediate complexes isomerize to give the products.