Impact of structure of donors and temperature on 1,2-dimethoxybenzene complexes in non-polar medium by acoustic, spectroscopic and DFT methods

This study summarises the influence of amine donor structure on the physicochemical properties of four ternary liquid mixtures consisting of 1,2-dimethoxybenzene (DMB) as the hydrogen acceptor and n-hexylamine (NHA), cyclohexylamine (CHA), aniline (ANI), and o-toluidine (OT) as hydrogen donors in n-hexane at different temperatures and 101 kPa pressure. Physicochemical parameters of these solutions as a function of equimolar concentrations in the range 0.02–0.2 M of ether and amine showed formation of strong solute–solute complexes between unlike molecules through non-covalent interactions and structural changes in the four systems. The free energy of formation (ΔG), enthalpy changes (ΔH), and entropy changes (ΔS), determined from the stability constants (K) as a function of temperature and compared with complex stability. UV–Vis spectra were characterised using the Benesi–Hildebrand approach and stability constants were deduced. Density Functional Theory (DFT) confirmed non-covalent and Van der Waals interactions between amines and ether in n-hexane. Experimental stability constants (K) correlated with computed interaction energies. Complex stability depends on donor structure and decreases in the order DMB − OT > DMB − ANI > DMB − CHA > DMB − NHA, which is discussed based on structures and types of interactions.