Tuning the C–X…π interaction of benzene–chloroacetylene complexes by aromatic substitutions

The interaction between chloroacetylene (C2HCl) and substituted benzenes has been investigated using density functional theory (DFT), MP2, and CCSD(T)/CBS methods. The results derived from these calculations revealed predominant non-covalent π…ClC2H interactions in all cases. The predicted interaction energies for substituted benzene/ClC2H complexes span a narrow range from −1.61 to −3.96 kcal/mol, indicating that the π…ClC2H interaction is comparable in strength to well-documented C–H…π interactions. The trend for interaction energies was found to be hexafluorobenzene–ClC2H < sym-tetrafluorobenzene–ClC2H < sym-trifluorobenzene–ClC2H < sym-difluorobenzene–ClC2H < benzene–ClC2H < sym-dimethylbenzene–ClC2H < sym-trimethylbenzene–ClC2H < sym-tetramethylbenzene–ClC2H < hexamethylbenzene–ClC2H. We have shown that electron-withdrawing groups weaken the complex, whereas electron-donating groups strengthen the interaction energy of the complex.