Concentration-induced hydrogen-bonding reorganization in acetic acid-dimethyl sulfoxide mixtures

Hydrogen bonding (HB) is a ubiquitous intermolecular interaction in nature, and its formation, strength variation, and network reorganization govern the structure, properties, and functions of matter. A comprehensive understanding of the HB behavior of polar functional groups, such as carbonyl groups, in complex solvent environments is essential for elucidating the physicochemical mechanisms underlying solution phase transitions and molecular recognition. In this work, a binary system composed of acetic acid (AA) and dimethyl sulfoxide (DMSO) was investigated, and intermolecular interactions at different concentrations were characterized using Raman spectroscopy. With increasing DMSO concentration, the carbonyl (CO) vibrational band of AA exhibited both high and low wavenumber, indicating the existence of intermolecular interactions between AA and DMSO. Meanwhile, the stretching vibration of the methyl (CH₃) group in DMSO showed a high wavenumber. A new component was observed at 1716 cm^-1, which belongs to the CO stretching vibration related to the CH₃ group. By combining density functional theory (DFT), two-dimensional correlation spectroscopy (2DCOS) analysis, and reduced density gradient (RDG) analysis, it was found that when the volume fractions of AA in the AA-DMSO system were 0.3 and 0.8 respectively, significant changes occurred in the Raman shift of CO. This study not only deepens the understanding of intermolecular interactions in carboxylic acid-sulfone solvent systems, but also reveals the physicochemical laws governing polar-group HB under external solvent perturbation, thereby providing a physicochemical basis for understanding the reorganization of HB in complex solution systems.