Structure-dependent intermolecular interactions in benzaldehyde/cinnamaldehyde –chlorophenol–hexane ternary liquids: An integrated FTIR and thermoacoustic properties investigation

This study presents an integrative approach, correlating spectroscopic evidence of molecular interactions with incremental variations in macroscopic properties such as density (ρ), viscosity (η), and ultrasonic velocity (U), to elucidate the behavior of multicomponent liquid mixtures. Accordingly, FTIR spectroscopy was used to identify the molecular-level interactions, to interpret the changes in thermoacoustic properties and molar excess parameters of the two ternary liquid mixtures:benzaldehyde (BA) + 2-chlorophenol (CP) + n-hexane (NH) and cinnamaldehyde (CA) + CP + NH. These aspects were systematically investigated for different mole fractions of the liquid components (BA,CA, CP and NH) at four temperatures ( T = 293.15–308.15 K). Experimental measurements of ρ, η and U were used to evaluate the key thermoacoustical parameters such as adiabatic compressibility (β), intermolecular free length (L_f), free volume (V_f), internal pressure (π), and specific acoustic impedance (Z), along with their corresponding excess functions (βₐ_dᴱ, L_fᴱ, V_fᴱ, πᴱ, and Zᴱ). The experimental U values were analyzed using Nomoto (U_N), Impedance (U_IR), and Rao (U_R) relations, and model suitability was assessed through average percentage deviation (APD). The results reveal pronounced non-linear composition dependence and significant temperature sensitivity in both systems. Comparative analysis shows that the CA-based mixtures exhibit lower ρ, η, u, and Z and higher βₐ_d and V_f than the BA-based system, indicating looser molecular packing and weaker associative interactions. FTIR spectral analysis confirms O–H···O=C hydrogen-bonded complexes between CP and the aldehydes, with stronger interactions in the BA system and weaker, more delocalized associations in the CA system due to extended π-conjugation.