Non-linearity of weak B⋯H–C hydrogen bonds: an investigation of a complex of vinyl fluoride and ethyne by rotational spectroscopy

Rotational and centrifugal distortion constants were determined for seven isotopomers of a weakly bound complex of vinyl fluoride and ethyne. The complex is planar or nearly planar, with a H of HCCH forming a hydrogen bond to the F atom of vinyl fluoride. The r0 geometry is: r(F⋯H)=2.441(4) Å, φ=122.7(4)° and θ=36.5(2)°, where φ is the angle made by the F⋯H internuclear line with the C–F internuclear axis and θ is the angular deviation of the F⋯H–C nuclei from collinearity. The non-linearity θ is attributed to the effect of a secondary interaction involving the π-bond of ethyne with one of the H atoms on C2 of vinyl fluoride. The angular geometry of C2H3F⋯HCCH is compared with those of other species C2H3F⋯HX.