Effective orientation of water in 1,4-dioxane···water: the rotational spectrum of the H2 17O isotopologue

Conformational Landscape of the Hydrogen-Bonded 1-Phenyl-2,2,2-Trilfuoroethanol···1,4-Dioxane Complex: Dispersion Interactions and Conformational Conversion

A rotational spectrum of the hydrogen-bonded complex between 1-phenyl-2,2,2-trilfuoroethanol (PhTFE), a chiral fluoroalcohol, and 1,4-dioxane, a common solvent for organic reactions, was measured using a chirped pulse Fourier transform microwave spectrometer. Initial theoretical conformational searches were carried out using CREST, a recently developed conformational searching tool. Subsequent geometry optimization and harmonic frequency calculations at the B3LYP-D3(BJ)/def2-TZVP level of theory yielded nearly 30 binary conformers of which 13 are within an energy window of ∼5 kJ mol^-1. Interestingly, while the O-H···O hydrogen bond dominates the attractive binary interactions, the complex conformational landscape is mainly controlled by subtle dispersion interactions between the phenyl and 1,4-dioxane rings. Two sets of rotational transitions were assigned in the experimental spectrum and attributed to the two most stable conformers of PhTFE···1,4-dioxane. The quantum theory of atoms in molecules (QTAIM), noncovalent interactions (NCI), and symmetry-adapted perturbation theory (SAPT) analyses were employed in order to appreciate how the phenyl ring and O-H functional groups influence the intermolecular interaction and conformational distribution of the binary complex. The main PhTFE conformation within the complex, identified experimentally, is different from that of the isolated PhTFE monomer reported previously.

A rotational study of the 1:1 adduct of ethanol and 1,4-dioxane

The pure rotational spectra of the 1:1 ethanol - 1,4-dioxane complex and its OD mono-deuterated species have been measured using pulsed-jet Fourier transform microwave spectroscopy. Conformational predictions for the plausible isomers of ethanol - 1,4-dioxane have been carried out considering the spatial orientation of gauche/trans ethanol with respect to the chair/boat and twisted conformations of 1,4-dioxane. Using Helium for the supersonic expansion, the microwave spectrum has been observed for the most stable structure. In the observed isomer, the two subunits are linked together by an OH⋯O hydrogen bond with gauche ethanol acting as proton donor to dioxane in the chair conformation. The non-covalent interactions have been characterized using different computational approaches. A small inverse Ubbelohde effect was observed after H → D isotopic substitution in the OH⋯O hydrogen bond.