Subtle solvation behaviour of a biofuel additive: the methanol complex with 2,5-dimethylfuran

Abstract

Methanol is shown to engage two nearly equivalent solvation sites in 2,5-dimethylfuran, the electron-rich π cloud and the electron-deficient oxygen site. The latter only wins by a slight margin, thanks to the methyl group undergoing secondary interactions with the ring. These secondary attractions reduce the hydrogen bond-induced OH frequency shift of the OH-O contact, whereas the π cloud allows for a combined action of both binding mechanisms in the OH-π arrangement. In total, the hydrophobic character of 2,5-dimethylfuran is well reflected in the weak pair interactions, as judged by the small solvation shifts. Methanol solvation of 2,3-benzofuran is revisited and shown to be more ambiguous than previously thought, involving competition between five- and six-ring π clouds and the oxygen site for the OH group. The six-ring π cloud is slightly preferred. FTIR spectroscopy in supersonic jets is in systematic agreement with dispersion-corrected harmonic B3LYP and also B2PLYP predictions for these competing furan docking sites. Deuteration of the OH group helps to identify the docking sites because of its attenuated zero-point energy weakening effect on localized hydrogen bonds. Extension to less methylated furans is proposed in the context of a future forecasting competition for the performance of quantum chemical methods for intermolecular interactions.

Intermolecular dissociation energies of hydrogen-bonded 1-naphthol complexes

“…Analogous methanol·furan and methanol·2,5-DMF complexes have been investigated by IR spectroscopy in slit supersonic jets, with a focus on the relative energies of the OH· · ·O and OH· · · π forms, also termed an "intermolecular energy balance". [56][57][58] Here, we provide the absolute dissociation energy, albeit with 1-naphthol replacing methanol as an H-bond donor. Finally, we compare the experimental D 0 values to those calculated with the widely-used dispersion-corrected density functional theory (DFT) methods B3LYP-D3, B97-D3 and ωB97X-D. [8][9][10][11]59 II.…”

Multi-spectroscopic and theoretical analyses on the diphenyl ether–tert-butyl alcohol complex in the electronic ground and electronically excited state

“…ref. [9][10][11][12][13][14] can be expected. The Fujii group 15 investigated clusters of 1-naphthol with methanol, ethanol, tert-butyl alcohol and water using combined IR/UV spectroscopy and assigned exclusively OH-O isomers for all clusters with the hydroxyl moiety of 1-naphthol acting as a hydrogen bond donor.…”

“…However, there are two experimental variations which can at least provide hints at the origin of the three mixed bands. 14 One is the addition of argon, which typically promotes the most stable 1 : 1 dimer due to improved collisional relaxation (bottom trace). This is the case for the least shifted band, but there is a potential problem with this conclusion.…”

Weak hydrogen bonding competition between O–H⋯π and O–H⋯Cl

“…Methanol is shown to engage two nearly equivalent solvation sites in 2,5-dimethylfuran, the electron-rich p cloud and the electron-decient oxygen site. 10 The OH group of methanol prefers to coordinate a 2,5-dimethylfuran molecule at its oxygen site, but largely because the methyl group simultaneously solvates the aromatic ring. The competing p solvation by the OH group is only marginally less stable but shows a signicantly larger bathochromic shi in the experimental infrared spectrum.…”

“…The competing p solvation by the OH group is only marginally less stable but shows a signicantly larger bathochromic shi in the experimental infrared spectrum. 10 Similarly, anisole also can offer two attractive hydrogen bond acceptor sites to an incoming hydrogen bond donor: its oxygen atom and its delocalized p electron system. Infrared absorption spectroscopy in the OH stretching fundamental range applied to a cold supersonic jet expansion of anisole and methanol in helium shows that the oxygen binding site is preferred.…”