Are the CF ₃ groups in 2,2-bis(trifluoromethyl)oxirane eclipsed or staggered? Insights from rotational spectroscopy and quantum chemical calculations

The pure rotational spectrum of 2,2-bis(trifluoromethyl)oxirane has been recorded using a chirped pulse Fourier transform microwave spectrometer. A total of 317 transitions have been recorded and spectroscopic constants have been determined for the first time. Quantum chemical calculations suggest that at equilibrium the two CF ₃-groups have a slightly staggered configuration with respect to one another. However, the barrier to an eclipsed configuration is calculated to be very low, ≈10 cm ^-1. Arguments are presented suggesting that the zero-point energy of the molecule is above the barrier to the CF ₃ eclipsed structure such that the zero-point geometry can reasonably be described as possessing eclipsed CF ₃-groups.