Structural and dynamical features of the 2,2,2-trifluoroethanol⋯ammonia complex

Abstract

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 TFE⋯NH₃ conformer and seven deuterium and ¹⁵N isotopologues were identified, and this led to a determination of partial r_s and r_o 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–H⋯N hydrogen-bond and secondary N–H⋯F 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.