Conformations of propargyl alcohol and its interaction with acetylene: A matrix isolation infrared and DFT computations

Abstract

Conformations of propargyl alcohol (PA) were studied using matrix isolation infrared spectroscopy. DFT computations using 6–311++G(d,p) basis set on the PA molecule identified two minima; gauche (g-PA) and trans (t-PA). Comparison of infrared spectra of PA trapped in Ar, N2 and Xe matrices with computations showed the evidence of the ground state g-PA conformer. Four minima were optimized on the potential energy surface for the hydrogen-bonded interaction of g-PA and acetylene (C2H2), corresponding to complex A (CH⋯O), complex B (OH⋯π) and complex C and D (CH⋯π). The structure, energies and the vibrational wavenumbers were computed for these complexes at B3LYP/6–311++G (d,p) level of theory. The infrared spectra of the hydrogen-bonded complexes between C2H2 and g-PA were studied in Ar matrix. The infrared spectra recorded under matrix isolation conditions revealed the formation of two types of complexes A (CH⋯O) and B (OH⋯π). Formation of these complexes was evidenced from the shifts in the vibrational wavenumber of the modes involving the C2H2 and PA submolecules.