Hydrogen bonding state of THF-H₂O solution analyzed by 2D Raman-COS spectroscopy

In this study, three distinct hydrogen bonding (HB) states of tetrahydrofuran (THF)-aqueous solutions at varying concentrations were characterized and analyzed using Raman spectroscopy coupled with two-dimensional correlation Raman (2D-COS) analysis. Specifically, in the range of 10%≤N_THF≤ 30%, the solution exhibits cluster structures characterized by free THF-5H₂O and THF-4H₂O tetrahedral configurations; in the range of 40%≤N_THF≤ 70%, the cluster structures within the solution consisted of THF·2H₂O and THF·H₂O configurations, following the fragmentation of tetrahedral structures; in 80%≤N_THF, the disruption of the tetrahedral structure of water enters the second stage, resulting in the formation of 2THF·H₂O and low-dimensional self-aggregated structures of THF. Combined with density functional theory, a further discussion on the changes in bond lengths and bond angles was conducted. The results indicate that with the increase of N_THF, the HB length initially shortens and then elongates, the dihedral angle first increases and then decreases, and the corresponding bond energy increases initially and then decreases.