Covalent character of three-center, two-electron systems -C2H3+ and C2H5+

MP2/6-311++G(3df,3pd) calculations were performed on C2H3+ and C2H5+ three-center, two electron (3c-2e) systems with T-shaped approach of proton to acetylene and ethylene, respectively. H+⋯π interactions possess the characteristics typical for covalent bonds. Two complexes: C2H5+⋯C2H2 and C2H3+⋯H2 were also considered where C2H5+ and C2H3+ act as proton donating systems while C2H2 and H2 as proton acceptors, respectively - these complexes possess the characteristics of H-bonded species.