Theoretical Computations for Ring-Puckering Potential Energy Functions of Fluorocyclobutanes

Abstract

Quantum chemistry computational methods have long been utilized to understand and calculate potential and kinetic energies of a system. MP2 ab initio method, based on the Møller-Plesset Perturbation Theory, has been used in this study to calculate the potential energy functions (PEFs) of fluorocyclobutane molecules. All possible substitutions of fluoride on the four-membered ring and their conformations have been investigated and the puckering angle and puckering coordinates of each molecule were calculated. The barrier to planarity and puckering coordinates were used to derive the PEFs. It was found that the angle strain has less an effect on the conformation of the molecules than the torsional forces, which makes the puckered conformation more favorable than the planar one. The expected symmetrical PEFs for selected molecules were calculated using a quartic equation relating both torsional forces and angle strain constants. Furthermore, the kinetic expansion function g(44)x was calculated for the selected symmetrical PEFs. The reduced mass was then used to obtain energy spacings of lower energy levels on the constructed PEFs. The results have shown agreement with experimental data, which indicated the applicability of this method to further understand other vibrational potential functions, including non-symmetrical PEFs.