Structure–properties relationships of deep eutectic solvents formed between choline chloride and carboxylic acids: Experimental and computational study

To implement different applications of deep eutectic solvents (DESs), the knowledge of their structure and properties should be enhanced. In this work, experimental characterizations together with theoretical calculations were employed to study the structure–properties relationships of seven ChCl-carboxylic acids DESs. The obtained DESs were analyzed using NMR spectroscopy to check their structures and interactions. The physicochemical properties of DESs, such as viscosity, conductivity, and Kamlet-Taft solvatochromic parameters, are closely related to the structure of carboxylic acids. A DES with more hydroxyl or carboxyl groups has a greater viscosity and a lower conductivity. Increasing the carbon chain of carboxylic acid reduces the polarity of the corresponding DES. Moreover, the calculation results from density functional theory (DFT) indicate that the type and intensity of intermolecular interaction of DESs are closely related to the structure of the carboxylic acid, which are consistent with experimental results. The systematic research on the structure–properties relationships expand our knowledge on the rational design of task-specific DESs.