Barriers to internal rotation in asymmetric molecules: 2,3-Difluoropropene

The potential function for internal rotation in 2,3-difluoropropene has been obtained from the microwave spectrum of the gauche rotamer, the far- and mid-infrared spectra of both the gauche and cis rotamers and the absolute rotational intensity measurements of several gauche microwave transitions. It is found that the cis conformer is most stable by 145 ± 60 cm⁻¹. Both the cis-gauche and gauche(+)-trans-gauche(−) barriers are approximately 1000 cm⁻¹. A comparison between the potentials in 2,3-difluoropropene, propene, and several other fluoropropenes is made. The dipole moment of the gauche conformer is μ_a = 0.950 D, μ_b = 1.982 D, and μ_c = 1.135 D; μ_total = 2.67 D.