Experimental And Theoretical Study Of The Solvent Effect On Some Reactions

Solvent effect plays important roles in many organic reactions. Selecting suitable solvent can enhancing reaction rate and improve yield, so the study of solvent effect has been received considerable attention from chemists. The study of solvent effect moves into the new step with the development of experiment method as well as computation science. In the present work, the effect of solvent polarity on organic reactions has been studied by both experimental and theoretical method1. Solvent effect on the Hilbert-Johnson Reaction has been studied by means of high pressure liquid chromatography (HPLC) and density functional theory (DFT) method. The study indicates that solvent plays an important role in the reaction, with the decreasing of the solvent polarity, the yield of the reaction and the ratio of a-anomer toβ-anomer both decrease. A new possible reaction pathway is proposed, which is a carbonium ion mechanism with a neighboring-group participation effect. The mechanism determines that theβ-anomer is the predominant product in the reaction.2. The oxidation of alcohol to the corresponding carbonyl compound is studied in both NBS/H2O2 and NBS/PEG systems. Both systems are efficient for primary and secondary aromatic alcohols as well as secondary aliphatic alcohols. In NBS/H2O2 system, N-bromosuccinimide and hydrogen peroxide play an essential role, without either N-bromosuccinimide or hydrogen peroxide, the reaction was slow and gave poor yield. In NBS/PEG system, it is assumed that the remarkable enhanced reaction rates could possibly be explained by the enhancement of the reactivity of NBS as a result of increased polarization of the N-Br bond in PEG medium Meanwhile, solvent effect is study in both experimental and theoretical aspects, the mechanism of the reaction is also proposed.3. High-pressure induced 1,3-dipolar cycloadditions of azides with both electron-deficient and electron-rich olefins are studied. The results reveal:on one side, concerted mechanism is preferred for this two types of reaction, and high-pressure can not only induce the cycloaddition with electron-deficient olefins but maybe also electron-rich ones from theoretical point of view; on the other side, the predominant product for the reaction of azides with electron-deficient olefins is different from that with electron-rich olefins. Meanwhile, for both electron-deficient and electron-rich olefins, increasing the polarity of the solvent can facilitate the formation of the products and at the same time stabilize the transition state.4. The isomers of thymine in gas phase as well as in the solution (water and methanol) are systematically studied by various quantum chemical methods, and the diketo form is the most stable isomer in both gas phase and solution. In order to investigate the different relative stabilities in gas phase and in solution, solvent effect and the dipole moment of all the isomers are also calculated, the results indicate that the dipole moment of all the 13 tautomers increases from gas phase to methanol and reaches the maximum in water. Meanwhile, the dipole moment has some relationship with the solvation energy, and the solvation energy of isomer with larger dipole moment is larger than that with smaller dipole moment. Meanwhile, with the purpose of investigating the relationships between these isomers, the isomerization process of the tautomers and the related barrier height are determined at various temperature.