Investigation of propyl ethanoate + C6–C10 1-alkanols: experimental properties, molecular dynamics, and quantum chemical insights

Abstract

Accurate knowledge of thermophysical properties and their molecular structural origins is essential for understanding liquid organization in associating mixtures. In this work, the density and viscosity of propyl ethanoate (PE) + C₆–C₁₀ 1-alkanol mixtures were measured over the full composition range at several temperatures, and the corresponding excess molar volumes (V^E) and viscosity deviations (Δη) were determined. To elucidate the structural origins of this behavior, molecular dynamics (MD) simulations and density functional theory (DFT) calculations were combined with experimental observations. Radial and spatial distribution functions reveal that alcohol–alcohol self-association dominates through directional hydrogen bonding, forming transient hydrogen-bonded clusters with dual-donor/acceptor configurations. In contrast, alcohol–ester hydrogen bonding is highly site-specific, occurring exclusively at the ester carbonyl oxygen with significantly weaker intensity. Atoms-in-molecules (AIM) analysis quantifies this interaction hierarchy: ROH–ROH binding energies strengthen from −8.24 to −11.31 kcal mol⁻¹ with chain length due to cumulative dispersion interactions, while ROH–PE interactions remain invariant at ∼−8.30 kcal mol⁻¹. Void space analysis further demonstrates that the disruption of alcohol hydrogen-bond networks by PE creates expanded free volume, with cavity radii distributions shifting toward larger voids as temperature increases. This structural asymmetry provides a quantitative molecular basis for the observed positive excess molar volumes and negative viscosity deviations, establishing a direct link between hydrogen-bond topology, void distributions, and macroscopic thermophysical behavior in ester–alkanol systems.