On the weak O–H•••halogen hydrogen bond: a rotational study of CH3CHClF•••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 Hw) = 2.14 A ˚ , and with two C–H O contacts to the alkyl hydrogens with r(C1–H1 Ow) = 2.75 A ˚ and r(C2–H2 Ow) = 2.84 A ˚ , 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.