Experimental and DFT Investigation of Thermodynamic and Acoustic Properties of N-Methylcyclohexylamine + m-Xylene + 1-Alkanol Ternary Mixtures: Insights into Molecular Interactions

Experimental densities and ultrasonic velocities were determined at 303.15 K for ternary mixtures of N-methylcyclohexylamine (NMC) (1), m-xylene (2), and 1-propanol, 1-butanol, or 1-pentanol (3) over the complete composition range. The obtained experimental values were used to calculate the excess molar volume (V₁₂₃ᴱ), isentropic compressibility (Kₛ₁₂₃), and deviation in isentropic compressibility (ΔKₛ₁₂₃). These derived properties provide valuable insight into the molecular interactions and structural effects present within the investigated ternary liquid systems. Using several prediction models, the excess characteristics ΔV₁₂₃ᴱ and ΔKₛ₁₂₃ were further estimated from the respective constituent binary systems, and the computed values demonstrated satisfactory agreement with the experimental results. Density Functional Theory (DFT) calculations were carried out at the B3LYP/6-311G (d,p) level of theory in order to gain a better understanding of the molecular interactions controlling the mixing behavior. The strength and kind of intermolecular interactions within the ternary systems were examined using optimized molecular geometries, molecular electrostatic potential (MEP) surfaces, frontier molecular orbital (HOMO–LUMO) studies, and interaction energy estimates. Hydrogen bonding, dipole–dipole interactions, and dispersive forces are the main factors influencing the thermodynamic and acoustic properties of the investigated mixes, according to the combined experimental and theoretical studies.