Study Of Hydrogen Bonding In Typical Organic-Water Binary Solutions By Raman Spectroscopy

In this paper,intermolecular interactions and corresponding hydrogen bonding structures in aqueous solutions of dimethyl sulfoxide?DMSO?,acetic acid,and methanol have been studied using spontaneous Raman spectroscopy,respectively.The information of molecular vibration and rotation can be obtained directly by measuring the Raman spectrum of the solution and analyzing the frequency shift of the characteristic peaks of organic molecules,which is helpful to understand the vibration frequency of covalent bond in the aqueous solution of organic molecules with different concentrations,so as to accurately analyze the microphysical process of hydrogen bond and cluster structure in the aqueous solution changing with the external conditions.Firstly,the Raman spectra of DMSO-water binary solutions with different mixing ratio were measured and studied.We found that the Raman peaks of the symmetrical and asymmetric OH stretching vibration modes of water move quickly to lower frequencies when the volume fraction of DMSO is less than 0.6,and the frequency shifts of the symmetric and asymmetric OH stretching modes are completely opposite when the volume fraction of DMSO exceeds 0.6.These results show that the strong hydrogen bond between DMSO and water molecules is helpful to strengthen the tetrahedral structure of water at a lower concentration,while the addition of DMSO molecules has a destructive effect on the structure of water at a higher concentration.Moreover,the blue shift of the Raman peak of S=O group increases obviously when the volume fraction of DMSO exceeds 0.6,which indicates that the cluster structure between DMSO and water molecules may have changed greatly.In addition,the Raman peaks of C-H groups with different vibration modes were studied.It was found that the non-polar methyl group of DMSO had hydrophobic hydration with water molecules.Secondly,the Raman spectra of acetic acid-water binary solutions with different mixing ratio were measured and investigated.The results show that there are two inflexion points in the spectrum when the volume fraction of acetic acid reaches 0.3and 0.8 respectively,corresponding to two structural changes of acetic acid-water clusters.Moreover,the Raman peak of C-H group undergoes a significant blue shift when the volume fraction of acetic acid reaches 0.8,which is caused by the structural change of the acetic acid-acetic acid cluster,indicating the formation of acetic acid side-on dimers.At last,the detailed changes of the cluster structure?hydrated monomer,linear dimer,acetic acid side-on dimer and water-separated dimer?in the acetic acid aqueous solution were obtained through theoretical analysis.Finally,the Raman spectra of methanol-water binary solution with different mixing ratio are measured and discussed.The results show that the hydrogen bonding between methanol and water changes significantly when the volume fraction of methanol reaches 0.4,resulting in the corresponding cluster structure changes.In addition,we found that the C-O stretching vibration mode of methanol shows a significant blue shift when the volume fraction of methanol exceeds 0.4,while the symmetrical and asymmetric stretching vibration modes of C-H show a significant red shift.These experimental results show that the CH₃ group of methanol doesn't form hydrogen bonds with water molecules,and the red shift of C-H is affected by the hydrogen bond formation of C-O bond.The results of this paper are helpful to understand the physicochemical properties of aqueous solutions of DMSO,acetic acid,and methanol,and further advance related research on hydrogen bonding and solvation effects of these three types of organic molecular aqueous solutions in the related fields of life sciences and chemical synthesis.