On the weak O-H⋯halogen hydrogen bond: A rotational study of CH 3CHClF⋯H2O

We measured the molecular beam Fourier transform microwave spectra of six isotopologues of the 1:1 adduct of CH3CHClF with water. Water prefers to form an O-H⋯F rather than an O-H⋯Cl hydrogen bond. This is just the contrary of what was observed in the chlorofluoromethane-water adduct, where an O-H⋯Cl link was formed (W. Caminati, S. Melandri, A. Maris and P. Ottaviani, Angew. Chem., Int. Ed., 2006, 45, 2438). The water molecule is linked with an O-H⋯F bridge to the fluorine atom, with r(F⋯H w) = 2.14 Å, and with two C-H⋯O contacts to the alkyl hydrogens with r(C1-H1⋯Ow) = 2.75 Å and r(C2-H2⋯Ow) = 2.84 Å, respectively. Besides the rotational constants, the quadrupole coupling constants of the chlorine atom have been determined. In addition, information on the internal dynamics has been obtained. © the Owner Societies 2011