C-H···π interactions involving acetylene: an ab initio MO study

Abstract

Ab initio MO calculations on the weak complexes of acetylene with CH₃Cl, CH₂Cl₂ and CHCl₃, provide qualitative and quantitative insights into the nature of the C-H···π interaction in these species. Cooperative C-H···C(π) interactions stabilize the HCCH···(CH₃Cl)₂, HCCH···(CH₂Cl₂)₂ and HCCH···(CHCl₃)₂ complexes. The interaction energies at the MP2/6-311+G(df,pd)//MP2/6-31G(d,p) level of theory, including ZPE contributions, and corrected for the basis set superposition error (BSSE), amount to 1.75, 2.27 and 2.91 kcal/mol, respectively. An energy decomposition analysis shows the variation of the different components as a function of the increase in polarity of the C-H bond. The electron correlation contribution is the most significant component of the binding energy.