Hydrogen bonding interactions in the 1,1,1,3,3,3-hexafluoro-2-propanol•••1,4-dioxane complex: Rotational spectroscopy and density functional theory calculations

The rotational spectrum of the binary complex formed between 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) and 1,4-dioxane was investigated using a chirped pulse Fourier transform microwave spectrometer. HFIP is known to be an exceptional solvent that catalyzes the epoxidation of olefins by hydrogen peroxide. The addition of 1,4-dioxane can severely reduce HFIP's ability to boost the epoxidation rate, possibly through its intermolecular interactions with HFIP. It is therefore of considerable interest to examine the non-covalent interactions between HFIP and 1,4-dioxane in detail. Theoretical conformational searches were carried out for the binary HFIP center dot center dot center dot 1,4-dioxane complex and 17 minimum energy structures were identified. Seven of them are within an energy window of 7 kJ mol(-1), while the three lowest energy ones are within 1.4 kJ mol-1. Experimentally, only the rotational spectrum of the most stable conformer was detected and assigned. To understand the non-observation of the other low energy conformers in the supersonic jet expansion, subsequent analyses were performed to estimate the conformational conversion barriers. The detected conformer contains a trans HFIP subunit which is hydrogen-bonded to an O atom of 1,4-dioxane and is further stabilized by weak F center dot center dot center dot H attractive interactions. The intermolecular interactions in HFIP center dot center dot center dot 1,4-dioxane were analyzed and visualized using QTAIM, NCI and SAPT approaches and the interaction energies compared to the HFIP dimer and related complexes of HFIP and 1,4-dioxane with water. (C) 2020 Elsevier Inc. All rights reserved.