| Molecular association is a spontaneous and equilibrium process by which molecules associate to form complexes and/or aggregates under specific conditions. These phenomena are widely found in biological and non-biological systems. The study of properties of associating systems is not only a traditional but also a precedingfield, and attracts chemists at all times.Classic definition for association is the effect of hydrogen bond. For a long time,most of the thermodynamic and experimental studies are concentrated on the strong hydrogen bonds in the system. Many thermodynamic models are proposed. Thermodynamic properties such as vapor-liquid equilibrium, excess volumn and excess enthalpy are mostly studied.Recently, spectroscopy may be utilized to probe microscopic properties such as intermolecular interactions and solution structure. This approach can provide physically meaningful molecular parameters and fundamental insight for development and testing of theory. Thus, spectroscopy such as IR, NMR, UV/vis, fluorescence spectroscopy, Raman, small-angle X-ray scattering and X-ray diffraction, neutron-scattering, MS and SEM has become the fourth vertex on the molecular thermodynamics tetrahedron. In these spectroscopic experiments, evidences of weak contacts of molecules, weak hydrogen bond are found. They are believed to play an important role in many systems and are becoming hotspot in today's research works.Alkanols are the most popular, presentative, and wide studied association systems. In despite of numerous studies on them, there still remays many questions, especially on the relation between classic hydrogen bond and weak hydrogen bond. In this thesis, thermodynamic theory, NMR experiment, quantumn chemical calculation and molecular dynamics simulation are used to study not only the OH…O hydrogen bond association but also the OH…O weak hydrogen bond association in alkanol systems. Also include the cooperative effects between them.In the second chapter of this thesis, the developments of lattice fluid theory are summarized. And then we decend to particulars of the latiice fluid theory with hydrogen bond (LFHB ) . Both physical and chemical parameters are discussed indetail. The emphasis is put on the physical meaning of the chemical item of the theory.In the third chapter, LFHB theory is applied to correlate the chemical shift of association solution of alkanol+alkane, and the results shows the model can be used to correlate the chemical shift of such associating mixtures. The gotten 5 f s are physically meaningful. This reveals the chemical meaning of the hydrogen bond extent calculated from LFHB.A development of LFHB is to introduce the cooperative effects into the original EOS. In the fourth chapter we compared the correlation results for alkanol systems with LFHB and cooperative LFHB. Better results are gotten with the cooperation effects included. The calculated hydrogen bond extents in cooperative LFHB are in good agreement with that from chemical theory correlation. While those results from original LFHB are not so good.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. All chemical shifts data of different kinds of protons are picked up over the whole concentration, including the *H NMR chemical shift data of the OH and CH2 or CH3 of alkanol, and the ]H NMR chemical shift data of the CH of benzene. Interesting orderliness is found. Then we use LFHB and cooperative LFHB to correlate both the experimental chemical shift data and data from literature of alkanol+benzene. Results are not satisfactorily.Clusters of alkanols are optimized and calculated in the sixth chapter using Gaussian 98 at RB3LYP/6-311G(d,p) level. Both linear and cyclic clusters up to 5 molecules are studied. Some of them are the first time to be studied and reported. Weak hydrogen bond of CH---0 is found to play an important role in these clusters. Cooperative factors are defined and calculated. NMR calculations are carried out to explain the different effects of the hydrogen bond and weak hydrogen bond on the chemical shift of protons. The calculations are helpful in explaining the reasonability of the LFHB correlation.In the seventh chapter, an all atom molecular dynamics simulation is carried out to study the pure methanol at seven temperatures. 0H---0 hydrogen bond extent and CH--0 weak hydrogen bond extent is calculated. It is found that the weak hydrogen bond plays a more important role at higher temperature. We use this result and theconclusion from the quantumn NMR calculation to explain the experimental NMR chemical shift of methanol. Then we apply MD simulation on the system of methanol+benzene under whole concentration. Weak CH---0 also helps to account for the interesting orderliness of NMR experiments.In the eighth chapter, we summarized our work and come up with some view for the future work.
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