An ab initio study of the molecular properties of the propyne–water hydrogen-bonded complex

Abstract

We have employed ab initio MP2 and DFT/B3LYP calculations with the 6-31++G(d,p) basis set to obtain structural, electronic and vibrational properties of the H-bonded complex between propyne and water. This study has revealed that H 2O can doubly complex with propyne forming a quasi five-membered ring. The first complexation occurs through the hydrogen bond between the acid hydrogen of H 2O and the C C triple bond, whereas the second complexation involves the oxygen atom of H 2O and the in-plane hydrogen atom of the methyl group in propyne. Our calculations have shown that the H-bond lengths between H⋯π and O ⋯ H in-plane ( H 3 C ) are 2.419 and 2.707 Å, respectively, employing the DFT/B3LYP calculation whereas the corresponding MP2 values are 2.373 and 2.651 Å. The binding energies including both BSSE and ZPE corrections are −6.16 and −6.72 kJ mol −1, respectively, using the DFT/B3LYP and MP2 calculations. For example, the O–H stretching frequencies of water are decreased by −60 and −29 cm −1 using the DFT/B3LYP calculation, whereas the bending frequency is increased by +15 cm −1. As expected, the infrared intensities for the stretching modes are increased after complexation, especially involving the O–H b bond forming the hydrogen bond with the C C triple bond.