Ultrasonic, DFT and FT-IR studies on hydrogen bonding interactions in aqueous solutions of diethylene glycol

Abstract

The density, viscosity and ultrasonic velocity measurements were carried out in aqueous diethylene glycol (DEG) solutions at different concentrations and temperatures to illustrate the hydrogen bonding interactions of DEG with water. The main acoustic parameters such as isentropic compressibility (βs), acoustic impedance (Z), hydration number (Hn), intermolecular free length (Lf), classical sound absorption (α/f2)class and shear relaxation time (τ) were calculated based on the experimentally measured values. These parameters have been utilized to study the solute–solvent interactions in aqueous DEG solutions. Further, these results suggest that the clusters of likely complex DEG molecule form hydrogen bonding with five water molecules in aqueous solution. The quantum chemical calculations were also performed to study the hydrogen bonding interactions between DEG in g−g+t–tg−t conformation and five water molecules. Computations have been done by DFT method at B3LYP/6-311+g(d,p) level of theory to study the equilibrium structure of DEG monomer in gas phase, DEG–(water)5 interacting complex in gas and solvation phases and the vibrational frequency shift due to formation of intermolecular hydrogen bonding. The solvation phase study was carried out using Onsager's reaction field model in water solvent. The computed and scaled vibrational frequencies are in good agreement with the main features of the experimental spectrum when five water molecules are considered explicitly with DEG in g−g+t–tg−t conformation. The parameters such as optimization energy (Etotal), hydrogen bond length and dipole moment (μm) of the interacting complex are also presented and discussed within the light of solute–solvent interactions.