A Direct Link from the Gas to the Condensed Phase: A Rotational Spectroscopic Study of 2,2,2-Trifluoroethanol Trimers

Angewandte Chemie - International Edition

5 years ago

A Direct Link from the Gas to the Condensed Phase: A Rotational Spectroscopic Study of 2,2,2-Trifluoroethanol Trimers

Wolfgang Jäger, Nathan A. Seifert, Javix Thomas, Yunjie Xu

Rotational spectra of the three most stable conformers (I, II, III) of the ternary 2,2,2-trifluoroethanol (TFE) cluster were measured using Fourier transform microwave spectrometers, and unambiguously assigned with the aid of ab initio calculations. The most stable conformer, I, contains one trans-TFE subunit which is unstable in its isolated gas phase form. The study offers new insights into how the trans conformation is stabilized in TFE clusters of increasing size, and eventually becomes a dominant conformation in the liquid phase. A detailed analysis shows that while O−H⋅⋅⋅O−H and O−H⋅⋅⋅F−C hydrogen bonds are the most significant attractive interactions which stabilize all three conformers, the main driving force for the stability of I over III, which has all gauche-TFE subunits, is the attractive interaction of C−F⋅⋅⋅F−C contact pairs. A new type of three-point F⋅⋅⋅F⋅⋅⋅F attractive contact interaction is also identified. Staying in contact: How trans-2,2,2-trifluoroethanol (TFE) becomes a significant conformation in the liquid phase while it is unstable in the isolated gas phase is a much-debated topic. The experimental detection of a TFE trimer containing one trans-TFE subunit shows that the attractive C−F⋅⋅⋅F−C contact interactions play a key role in preferential stabilization of trans versus gauche-TFE in the trimer.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/anie.201612161