Highly correlated ab initio wave functions within the MRCI approach are used in a comparative study of the interactions between C-2 and the three hydrogen halides HX (X = F, Cl, Br). Test calculations are also presented using the UCCSD(T)-F12 approach. The asymptotic regions are investigated for different relative orientations of the two moieties. It is shown that the three systems C-2 + HX are bound, for intermolecular distances close to 3 angstrom, through nucleophilic interactions between C-2 and HX for approaches perpendicular to the C-C axis, with decreasing interaction energies from HF to HBr. For HX approaching C-2 along its axis, the interactions, governed by the electrophilic character of C-2 are decreasing from HBr to HF. Even though the reactions toward the molecular systems HCCX or CCHX are exothermic, activation barriers (0.58 eV and more) are calculated at short distances, preventing the direct reactions toward the corresponding tetra-atomic systems.