Hydrogen bond docking preference in furans: OHp vs. OHO.
The docking sites of hydrogen bonds in complexes formed between 2,2,2 trifluoroethanol (TFE) furan (Fu) and 2 methyl furan (MF) have been investigated. Using density functional theory (DFT) calculations, gas phase and matrix isolation FTIR spectroscopies, the strengths of OHO and OHp hydrogen bonds in the complexes were compared to find the docking preference. Calculations suggest that the hydrogen bond donor, TFE, is more likely to dock onto the oxygen atom of the aromatic furans ring, and consequently, the OHO type hydrogen bond is relatively stronger than the OHp type. The FTIR spectrum in the OH stretching fundamental range obtained at room temperatures has been compared with that obtained at extremely low temperatures in the matrix. The fundamental and the red shifts of OH stretching vibrations were observed in both FTIR spectra, confirming the formation of hydrogen bonded complexes. By assessing the ability of furan and MF to participate in the formation of OHO hydrogen bond, the effect of ring methylation has been highlighted. From the calculated geometric and thermodynamic parameters as well as the frequency shift of the OH stretching vibrations in complexes, TFE MF is found to be more stable than TFE Fu, which suggests that the strength of the OHO hydrogen bond in TFE MF originates from the high activity of the furan molecule caused by the methylation of the aromatic ring. The present study furthers the knowledge of docking preference in heteroaromatic molecules and is helpful to understand the nature of intermolecular interactions between hydrogen bond donors and acceptors, including both electron deficient atoms and p cloud.
Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy