Comparative Stability of 1-Methylcyclopropene and Methylenecyclopropane Tautomers: Ab initio and DFT Study

The geometric optimizations, relative stabilities, and infrared spectroscopy analyses of the 1-methylcyclopropene and methylenecyclopropane tautomers were all accomplished using a combination of CCSD and DFT methods. Data that demonstrate the relative stability of the endo-en and exo-en forms were examined. The thermodynamic results showed that methylenecyclopropane is the
more stable isomer at the B3LYP / aug-cc-PVDZ level of theory, with enthalpy (H=12.4kcal/mol and Gibbs energy (G=11.7kcal/mol) lower than that for 1-methylcyclopropene. These results and those from the preceding experiments are in perfect agreement. The vibrational frequencies and geometrical factors that were discovered in earlier studies also show strong consistency. Additionally, the CCSD/ aug-ccPVDZ level of theory was used to calculate molecular orbitals such as natural bond orbitals (NBOs), HOMO-LUMO energy gaps, and electrostatic potential (ESP) surfaces. It was explained how crucial it is to choose the most stable tautomer while manufacturing 1-methylcyclopropene (1-MCP), which is used to control fruit quality in the post-harvest environment.