Analysis of cis-Difluoroethylene Ozonide by Microwave Spectroscopy and ab Initio Techniques: An Unusual Conformational Potential

Article abstract of DOI:10.1021/j150654a019

The microwave spectra of five isotopic species of cis-difluoroethylene ozonide (cis-3,5-difluoro-1,2,4-trioxolane) were assigned, including the parent, both the d₁ and the d₂ species, and the symmetric double-18O and the triple-18O species.A series of vibrational satellites also accompanied the ground-state transitions.The average structure consistent with this data was an ether oxygen envelope conformation having C_s symmetry, with the fluorines axial to the ring.Ab inito calculations were performed for selected values of the pseudorotational phase angle Φ to provide additional insights.They indicated that the ether envelope corresponded to the minimum-energy conformer.The potential function vs. Φ was relatively flat near the minimum and did not possess a low-energy path corresponding to the usual pseudorotation motion.Instead, the energy valley connecting puckered forms at 180, 90, and 270 deg terminates at the planar form.The ground-state conformation was discussed in terms of the balance between ring-substituent, substituent-substituent, and puckering fores.Stabilizing ring-substituent interactions dominate this interplay and are also reflected in long C-F and short C-O bond distances indicative of anomeric interactions involving the fluorine substituents.