C-H center dot center dot center dot pi interactions involving acetylene: an ab initio MO study

Ab initio MO calculations on the weak complexes of acetylene with CH3Cl, CH 2Cl2 and CHCl3, provide qualitative and quantitative insights into the natu re of the C-H . . . pi interaction in these species, Cooperative C-H . . .C (pi) 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 contributi ons, and corrected for the basis set superposition error (BSSE), amount to 1.75, 2.27 and 2.91 kcal/mol, respectively. An energy decomposition analysi s shows the variation of the different components as a function of the incr ease in polarity of the C-H bond. The electron correlation contribution is the most significant component of the binding energy. (C) 2000 Elsevier Sci ence B.V. All rights reserved.