On the weak O–H⋯halogen hydrogen bond: a rotational study of CH3CHClF⋯H2O

Abstract

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⋯O_w) = 2.75 Å and r(C₂–H₂⋯O_w) = 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.