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

The weak intermolecular interaction between 2,2,2-trifluoroethanol (TFE) and 3-chloro-2-methyl-1-propene (CMP) has been investigated by gas phase FTIR spectroscopy and DFT calculations. CMP offers two hydrogen bond docking sites to the hydrogen bond donor: the chlorine atom (O-H⋯Cl) and the C=C π electron system (O-H⋯π). DFT calculations suggest that MeOH approaches CMP in five different orientations. The structural, energetic, and spectroscopic parameters of the most stable structures in each orientation were studied, and their binding energies range from -25.5 to -19.5 kJ mol^-1. The docking to the π system is at least 1 kJ mol^-1 more favored than the docking to the chlorine atom. The equilibrium constant for complexation (2.3 × 10^-2) was determined from the experimental and calculated intensity of the OH-stretching transition. The Gibbs free energy of formation was found to be 9.3 kJ mol^-1. The nature of the non-covalent interaction was analyzed with the atoms in molecules (AIM) method.