A theoretical study on the isomerization of cyclopropane to propene with ab initio and DFT methods

The isomerization of cyclopropane to propene had been studied by ab initio post-HF and DFT methods. Single-point energy calculations at UMP4, UCCSD(T), UQCISD(T) and UBecke3LYP levels were carried out on the UMP2/6-31G ** fully optimized structures. The reaction heat and activation energies for the whole isomerization reaction and the structural isomerization of the C₂-symmetry trimethylene intermediate were evaluated. The correlation methods employed release an accuracy order of UBecke3LYP > UQCISD(T) ≈ (UCCSD(T) ≈ UMP4 > UMP2. UBecke3LYP is found to be the best method to reproduce the experimental results. The spin contamination problem can be solved by using projected MP energies.