Structural and dynamical features of the 2,2,2-trifluoroethanolammonia complex

The 1 : 1 adduct of 2,2,2-trifluoroethanol (TFE) with ammonia was investigated using a combination of chirped pulse and cavity-based Fourier transform microwave spectroscopy and computational methods. Rotational spectra of the most stable TFENH3 conformer and seven deuterium and 15N isotopologues were identified, and this led to a determination of partial rs and ro structures. The observed complex exhibits a gauche conformation of TFE with ammonia inserted into the existing intramolecular hydrogen-bonded ring of TFE. The adduct is stabilised by a delicate interplay between the primary O-HN hydrogen-bond and secondary N-HF interactions between TFE and ammonia. Evidence for several internal-dynamics effects was found in the rotational spectra. The ammonia subunit shows an almost free internal rotation. Tunneling between the gauche forms, g+ and g-, of TFE is quenched by the hydrogen-bond interactions with ammonia.