Structure and bonding of 2,2,2-trichloroethylacetate: An experimental gas phase and computational study

Abstract

AbstractThe structural and conformational properties of 2,2,2-trichloroethylacetate, H3CCO2CH2CCl3, have been determined in the gas phase using gas electron diffraction (GED). The experimental measurements were complemented by MP2 and DFT quantum-chemical calculations. Two conformers separated by a shallow rotational barrier have been identified, one ofC1(syn-gauche) and the other ofCssymmetry (syn-anti). All calculations indicate thatsyn-gaucheis preferred in terms of enthalpy, whereassyn-antiseems to be slightly more stable regarding Gibbs free energy. In the gas-phase structure determination, dynamic models based on different potential energy surface scans were used. The one from dispersion-corrected density functional theory, predicting a preference ofsyn-gaucheby 1.7kJmol−1, was found to describe the experimental data best. One- and two-conformer models had to be rejected due to correlations and unrealistically large amplitudes. Experimentally determined structural parameters are in good agreement with both, quantum-chemical calculations as well as GED data for related compounds. Interacting quantum atoms (IQA) analyses revealed that interplay between the carbonyl group and the hydrogen as well as chlorine atoms of the trichloroethyl group accounts for most of the stabilisation of theC1conformer. With intramolecular symmetry-adapted perturbation theory (I-SAPT) analyses it was possible to further elucidate the nature of dominant interactions in the two conformers. Herein, preference ofsyn-gauchecan for the most part be attributed to electrostatic and to some extent to induction and dispersion interplays. In contrast this conformer is severely destabilised through steric repulsion. These results were supported by NBO analyses.