Studying Solution Thermodynamic Properties Of Associating Systems By ～1H NMR Chemical Shift

Molecular association is special phenomena, which are resulted from intermoiecular interaction and widely found in biological and non-biological systems. Because of the molecular association, many properties of solution are changed such as microstructure, excess volume, heat of mixing, spectroscopic property and so on. Attention has been attracted by the special properties of associating systems. The study of properties of associating systems is not only a traditional but also an attentive field.The spectroscopic properties exhibit properties of microstructure of the associated solution. Therefore, while the microscopic property of intermoiecular interaction changes with the concentration, the macroscopic property of spectroscopic information also shows some disciplinarian. Recently, since the spectroscopic technology has been developed, spectroscopy is utilized to probe microscopic properties such as intermoiecular interactions, solution structure and the relationships between the concentrations coupled with associated models. The commonly spectroscopy includes IR, NMR. UV/vis, Raman, neutron-scattering, X-ray diffraction and MS, which are widely used to research association solution. Using the spectroscopic technology to establish the relationship between the spectroscopic information and thermodynamic properties is a new field of investigating the associating systems.In this paper, NMR is selected to investigate the properties of association solutions. A new local composition model based on two-liquid theory has been proposed in second chapter. The model assumes there are two cells in the binary solution, one is the molecule 1 in the center and another is molecule 2 in the center. The chemical shift at any concentration is the sum of chemical shift in the cells. The model contains two parameters denoting the intermoiecular interaction energy.In the third chapter, the proposed local composition model was applied to correlate the chemical shift of association solution such as DMF/alcohol, NMA/water etc systems, and the results showed the model can be used to correlate the chemical shift of various associating mixtures, and the applicability is good. Assiuming that the model parameters do not change with temperature, and then the chemical shift of the same binary system at other temperature was predicted. The seven associating mixtures were tested as examples to study the influence of temperature on the mixing chemical shift, and the deviations for prediction were almost in the same magnitude with those of correlation.In the fourth chapter, OH chemical shift of alcohol + hexane, alcohol + cyclohexane, alcohol +benzene mixtures were correlated by semi-empirical local composition model developed by Deng et al. with one parameter. Using the parameter and coupled with one activity coefficient at infinite dilution, the vapor-liquid equilibrium (VLE) data of alcohol + hydrocarbon have been predicted at the different temperature. The relative deviations in the pressure and the absolute average in vapor phase composition are 5.00%. The good prediction results not only extend the applications of the local composition model, but also build some relationships between spectroscopic properties and thermodynamic properties.In the fifth chapter, the 'H NMR chemical shift of the methanol + benzene, ethanol + benzene and 1-hexanol + benzene mixtures at 302.15K were measured by the internal reference method. Based on the concept of local composition, the 'H NMR chemical shift data of the OH and CH over the whole concentration were correlated with only one parameter, respectively. Using the two parameters obtained from spec.ra alone, the isothermal and isobaric binary vapor—liquid equilibrium data of methanol + benzene and ethanol + benzene systems were predicted with satisfactory results. For the 1-hexanol + benzene system, the isobaric VLE data were also predicted. In this way, the spectroscopic information can be related to thermodynamic property directly.