Roles of the Ether Oxygen in Hydration of Tetrahydrofuran Studied by IR, NMR, and DFT Calculation Methods

Abstract

We studied the concentration dependence of nu(C-H)'s in IR and (1)J(C,H) in NMR for binary water-tetrahydrofuran (THF) mixtures and found different trends for the two types of CH(2) groups in the five-membered ring. The changes of the nu(C-O) spectra showed that complexes of THF associated with water are formed, in which the number of water molecules increases with the water concentration. We suggested that hydration proceeds through the formation of 1:1, and 1:2 complexes of [THF:water] up to X(H(2)O) approximately 0.9, where X(H)((2))(O) is the mole fraction of the water in the mixtures. We carried out ab initio MO and DFT calculations to optimize the geometries of a THF dimer as a model of THF molecules in pure liquid, and 1:1 and 1:2 complexes of [THF:water] to simulate observed concentration dependence of nu(C-H)'s in IR and (1)J(C,H) in NMR. The changes of the calculated nu(C-H) spectra and (1)J(C,H) values for the optimized complexes are in agreement with those observed with varying X(H)((2))(O), supporting our proposal. From the vibrational and NBO analyses of the optimized complexes, the observed blue shift of nu(C-H)'s and the increase of (1)J(C,H) for the CH(2) groups neighboring to the ether oxygen were explained in terms of the changes in the stereoelectronic effect, resulting from HO-H...O< hydrogen bonding. The optimized 1:2-complex contains two weak C-H...OH(2) hydrogen bonds, and blue shift of nu(C-H)'s and increase of (1)J(C,H) were demonstrated from the same analyses of the complexes. This result of simulation also supports that the blue shift of nu(C-H)'s and increase of (1)J(C,H) observed for both the type of CH(2) groups at 0.6 X(H)((2))(O) < 0.9 are attributed to these interactions. On the basis of all these results, we propose that the formation of the 1:2-complex involving weak C-H...OH(2) hydrogen bonds is responsible dominantly for the hydrophobic hydration of THF.

Infrared Spectroscopic Investigation of Photoionization-Induced Acidic C–H Bonds in Cyclic Ethers

“…Because of the similar features of the C 2 and C S conformers in this frequency range and their small energy difference, it is difficult to determine the The assignments of the vibrations of neutral THF have also been seen in the literature. 20, 23,24 The normal-mode analyses based on the C 2 conformer have been performed. 20 Details of the assignments, which are simulated at the ωB97X-D/6-311+ +G(3df,3pd) level in this study, in the CH stretch region are described in Table S2 of the Supporting Information.…”

Hydrogen Bonding between Water and Tetrahydrofuran Relevant to Clathrate Formation

“…guest; 17,36,37,42,43 the picture for the water host is less well developed. It is challenging to obtain experimental data about the host: its concentration is greater so the difficulty lies in deconvoluting small changes due to interaction from the larger concentration features.…”

“…These results complement previously reported work examining vibrations of the promoter. 17,37 The implication for clathrate formation is that the promoter modifies hydrogen bonding in the water host and that the modification is mitigated upon guest incorporation. Further experimental and theoretical work is needed to identify the ideal helper-water-guest interaction for low-pressure clathrate formation .…”

Solvent distributions, solvent orientations and specific hydration regions around 1-adamantyl chloride and adamantane in aqueous solution

“…In tetrahydrofuran-water mixtures, the C-HÁ Á ÁO interaction was observed using NMR and IR [29], and it was proposed that the formation of weak C-HÁ Á ÁOH 2 hydrogen bonds was responsible for the hydrophobic hydration of tetrahydrofuran. The present calculations indicate that the C-HÁ Á ÁO interaction is enhanced by halogen substitution even in the rear side of a large hydrophobic skeleton.…”