Microwave spectroscopic and computational analyses of the phenylacetylene⋯methanol complex: insights into intermolecular interactions

Abstract

The microwave spectra of five isotopologues of phenylacetylene⋯methanol complex, C₆H₅CCH⋯CH₃OH, C₆H₅CCH⋯CH₃OD, C₆H₅CCH⋯CD₃OD, C₆H₅CCD⋯CH₃OH and C₆H₅CCH⋯¹³CH₃OH, have been observed through Fourier transform microwave spectroscopy. Rotational spectra unambiguously unveil a specific structural arrangement characterised by dual interactions between the phenylacetylene and methanol. CH₃OH serves as a hydrogen bond donor to the acetylenic π-cloud while concurrently accepting a hydrogen bond from the ortho C–H group of the PhAc moiety. The fitted rotational constants align closely with the structural configuration computed at the B3LYP-D3/aug-cc-pVDZ level of theory. The transitions of all isotopologues exhibit doublets owing to the methyl group's internal rotation within the methanol molecule. Comprehensive computational analyses, including natural bond orbital (NBO) analysis, atoms in molecules (AIM) theory, and non-covalent interactions (NCI) index plots, reveal the coexistence of both O–H⋯π and C–H⋯O hydrogen bonds within the complex. Symmetry adapted perturbation theory with density functional theory (SAPT-DFT) calculations performed on the experimentally determined geometry provide an insight into the prominent role of electrostatic interactions in stabilising the overall structural arrangement.