Strength of non-covalent interactions and the thermodynamics of n-hexane solutions containing 1,4-dioxane + primary amine complexes: an ultrasonic, spectroscopic and computational study

The investigation explores the structural effect of hydrogen donors (primary amines) on interactions with 1,4‑dioxane (DIOX) and the thermodynamics of these complexes in n-hexane solution. Acoustical data for equimolar solutions (0.02 M to 0.2 M) of DIOX and primary amines (n-hexylamine (NHA), cyclohexylamine (CHA), aniline (ANI), or o-toluidine (OT)) at 297.15–306.15 K and 101 kPa indicate enhanced compactness due to strong non-covalent interactions overriding structure-breaking behaviour. Hyperchromicity and absorption-wavelength shifts in the UV spectra confirmed complex formation. Stability constants (K) as a function of temperature were computed from speed of sound and Benesi–Hildebrand plots of UV data, and both showed identical trends at ambient temperature. Thermodynamic properties from van’t Hoff plots and DFT calculations were used to assess the stability of the formed complexes, experimental K values, interaction energies, underlying non-covalent interactions, compactness, and the influence of amine structure on their overall thermodynamics in solution.