Excess Infrared Spectroscopy-Based Studies On The Structures And Probes Of Liquid Mixtures

Most chemical reactions,as well as extraction,purification and separation processes are carried out in liquid systems.So liquid chemistry is of great significance.Among them,a key issue is to investigate the structure and physicochemical properties of liquid systems.The microstructures of liquids are more complex than solids and gases,and acid-base character is one of the most important properties associated with liquid.In this thesis,the liquid structure and intermolecular interactions between ionic liquids and cosolvents were studied by excess infrared spectroscopy,infrared spectroscopy,nuclear magnetic resonance spectroscopy and quantum chemical calculations.In addition,method based on probes for detecting microstructures and physicochemical properties of liquids by means of spectral characteristics of specific functional groups has also been attempted.First,the structure and hydrogen bonding interactions in binary system of functionalized ionic liquid[C₂OHMIM][BF₄]and acetonitrile were investigated.For[C₂OHMIM]⁺,it was found that??O-H?is more sensitive to environmental changes than??C-Hs?,and can be used as an embedded infrared probe to reflect changes in liquid structure.With the help of excess infrared spectroscopy and quantum chemical calculation,the O-H stretching vibration region is studied in detail,the species of“cation-cation”and“cation-anion”complex and its dynamic transformation during the mixing process were identified.In addition,the strength and cooperativity of the doubly ionic hydrogen bonds were also analyzed.It was found that the“O-H···O”hydrogen bonds between two cations are cooperative,and the hydrogen bonds between the cation and the anion through“O-H··F”and“C2-H···F”were anti-cooperative.Second,the structure and halogen-/hydrogen-bond interaction modes in binary systems of ionic liquid[BMIM][BF₄]and halobenzenes C₆F₅X?X=I,Br,H?were investigated.The characteristics of“multi-state”and“two-state”in the excess infrared spectra of??C-I?and??C-Br?regions,indicates more complicated interactions modes in the[BMIM][BF₄]-C₆F₅X system.By analyzing the excess infrared spectra of??C-I?,??C-Br?and??COO^-?regions,combined with quantum chemical calculations,the hydrogen bonding and halogen bonding interaction modes between the ionic liquid and halobenzenes were identified.In the[BMIM][BF₄]-C₆F₅I system,three new complex,ion pair-C₆F₅I,anion-C₆F₅I and anion-2C₆F₅I were found,while in the other two systems only the newly formed ion pair-C₆F₅Br/C₆F₅H was observed.This is because the halogen bonding interaction between C₆F₅I and the ionic liquid is the strongest,which is strong enough to break up ion pairs.Third,a method for quantitatively characterizing the equilibrium acidity of a series of compounds by using nitrile probe was established.The changes of??C?N?in acetonitrile/benzonitrile probe molecules during the solvation by molecules with different p K_a values were investigated by infrared spectroscopy and excess infrared spectroscopy.It was found that there exist linear relationships between??C?N?of probe molecules and the p K_a values of the substance.Especially,the excess infrared spectra of trifluoroethanol-CH₃CN binary systems in whole concentration range were studied in detail.Then,the nitrile stretching frequencies of positive peaks were translated to multiple local p K_a values through the established linear relationships,which are consistent with calculated p K_a values related to different complex by DFT.Excess spectroscopy help us establish the correlation between macroscopic thermodynamic properties and microscopic structures.