title: Hydrogen bond docking site competition in methyl esters.
abstract: The OH⋯O hydrogen bonds in the 2,2,2-trifluoroethanol (TFE)-methyl ester complexes in the gas phase have been investigated by FTIR spectroscopy and DFT calculations. Methyl formate (MF), methyl acetate (MA), and methyl trifluoroacetate (MTFA) were chosen as the hydrogen bond acceptors. A dominant inter-molecular hydrogen bond was formed between the OH group of TFE and different docking sites in the methyl esters (carbonyl oxygen or ester oxygen). The competition of the two docking sites decides the structure and spectral properties of the complexes. On the basis of the observed red shifts of the OH-stretching transition with respect to the TFE monomer, the order of the hydrogen bond strength can be sorted as TFE-MA (119cm-1)>TFE-MF (93cm-1)>TFE-MTFA (44cm-1). Combining the experimental infrared spectra with the DFT calculations, the Gibbs free energies of formation were determined to be 1.5, 4.5 and 8.6kJmol-1for TFE-MA, TFE-MF and TFE-MTFA, respectively. The hydrogen bonding in the MTFA complex is much weaker than those of the TFE-MA and TFE-MF complexes due to the effect of the CF3substitution on MTFA, while the replacement of an H atom with a CH3group in methyl ester only slightly increases the hydrogen bond strength. Topological analysis and localized molecular orbital energy decomposition analysis was also applied to compare the interactions in the complexes.
authors.affiliation: Environment Research Institute, Shandong University, Shanda South Road 27, 250100, Shandong, China.
authors.forename: Hailiang
authors.initials: H
authors.lastname: Zhao
authors.affiliation: Environment Research Institute, Shandong University, Shanda South Road 27, 250100, Shandong, China.
authors.forename: Shanshan
authors.initials: S
authors.lastname: Tang
authors.affiliation: Environment Research Institute, Shandong University, Shanda South Road 27, 250100, Shandong, China. Electronic address: lindu@sdu.edu.cn.
authors.forename: Lin
authors.initials: L
authors.lastname: Du
keywords: AIM; FTIR; Hydrogen bond; LMO-EDA analysis; Red shift