H...π complexes of acetylene-benzene: a matrix isolation and computational study

Abstract

Hydrogen bonded H...π complexes of C₂H₂ and C₆H₆ were studied both computationally and experimentally. Computationally, C₂H₂-C₆H₆ complexes of 1:1 and 2:1 stoichiometries were identified. The molecular structure and stabilisation energies of the complexes were calculated at the HF, MP2, MP2(Full) and B3LYP levels of theory employing basis sets ranging from 6-31G(d,p) and 6-31++G(d,p) while the frequency calculations were performed at HF, B3LYP and MP2 levels using 6-31G(d,p) and 6-31G++(d,p) basis sets. Using matrix isolation infrared spectroscopy, we observed a 1:1 adduct in an argon matrix. Formation of the adduct was evidenced by shifts in the vibrational frequencies of the acetylene and benzene submolecules in the complex. Though our computations showed two types of 1:1 complexes-one where the acetylene is the proton donor and another where the benzene is the proton donor, experimentally, we observed only the complex, where acetylene acts as a proton donor to the p cloud of benzene.