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

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.