几个碳单环及双环分子环应力的理论研究

Theoretical prediction of ring strain energies of several carbon-monocyclic and carbon-dicyclic compounds

应用密度泛函方法对1-亚甲基-2-乙烯基环丙烷、3-亚甲基环戊烯、1-亚环丙基-2-乙烯基环丙烷和4-亚甲基螺[2,4]庚-5-烯四个体系的环应力进行了理论研究。对已有实验环应力值的模型反应研究结果表明,密度泛函方法下,采用hyperhom odesmotic反应计算模型所得到的结果可以反映出正确的环应力值。采用这种模型和方法,对所研究的四种环状分子环应力的计算结果表明,三元环的分子应力能已经使1-亚甲基-2-乙烯基环丙烷和1-亚环丙基-2-乙烯基环丙烷处于非常不稳定的状态,经过一步重排就可以生成3-亚甲基环戊烯和4-亚甲基螺[2,4]庚-5-烯,而且反应放热较多,环应力较大的反应物反应变成环应力较小的生成物的过程对反应放热起到了重要的作用。

The ring strain energies of the selected four compounds,1-methylene-2-vinylcyclo-propane,3-methylenecyclopentene,1-cyclopropylidene-2-vinylcyclopropane and 4-methyl-enespiro[2,4]hept-5-ene,were investigated by use of DFT methods.The investigated results for the model molecules whose experimental ring strain energy is available indicated that the combined density functional theory （B3LYP） and hyperhomodesmotic reaction model can give a reasonably theoretical ring strain energy.The computed results also show that the ring strain energies of there-membered with exocyclic double bond make 1-methylene-2-vinylcyclo-propane and 1-cyclopropylidene-2-vinylcyclopropane into an unstable state,and they can exothermically rearrange to form 3-methylenecyclopentene and 4-methyl-enespiro[2,4]hept-5-ene.The exothermic reaction comes from decreasing ring strain energies from reactants to products.