By means of coupled cluster and density functional M06-2X calculations we have studied the directionality and energetics of the hydrogen bond (HB) between halides and the following H donors: methane, ethylene, and acetylene. The largest interaction energy was obtained for acetylene, the molecule in which the hydrogen atoms present the largest positive charge. For the complex [X···HCCH]−, fluoride presented a different behavior since acetylene donates a hydrogen to fluoride and the [HF···CCH]− complex was formed. We found that for ethylene there is a strong competition between the monodentate- and bidentate-like structures. Because of its small size, fluoride leads to a monodentate complex with C2H4. However, as we move down in the periodic table, the bidentate-like structure becomes more stable. In effect, for chloride and bromide they are nearly isoenergetic, while for iodide the bidentate-like complex is formed. These present results question previous investigations about the directionality of the HB in halide–ethylene complexes.