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Studies on the Reaction Mechanism for the Synthesization of 5-Oxatric-Yclo[] Te-tradeca-1,3(7),8,10,12-Pentaene

Author: ZhangSen
Tutor: ZhangJingChang
School: Beijing University of Chemical Technology
Course: Industrial Catalysis
Keywords: 5-oxatricyclo[,7]tetradeca-1,3(7),8,10,12-penta-ene displacement reaction epoxidation reaction reaction mechanism transition states topological analysis of charge density
CLC: O621.13
Type: Master's thesis
Year: 2004
Downloads: 19
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The reaction mechanisms of displacement reaction and epoxidation reaction during the synthesis of 5-oxatricyclo[,7]tetradeca-1,3(7),8,10,12-pentaene have been studied by using ab initio molecular orbital theory and density functional theory(DFT). At B3LYP/6-31G* level, the geometrical structures of reactants, transition states and products along the reaction paths have been optimized with Berny energy gradient technique. The transition states were characterized by vibration frequency analysis, with only one imaginary vibration model. Then, the changes of the geometrical structures and the energies of the stationary points were analyzed by using the intrinsic reaction coordinate (IRC) method. Zero-point energy correction has been done along the minimum energy path(MEP) for each reaction. Finally, topological analysis of electron charge density is employed for investigating the changes of chemical bonds <WP=6>in the reaction process. The major conclusions can be summed up as follows: 1.The activation barrier of the displacement reaction is 157.67kJ/mol, and the reaction is endothermal by 18.78kJ/mol. The activation barrier of the epoxidation reaction is 139.23kJ/mol, and the reaction is exothermic by 25.16 kJ/mol. So the two reactions can be proceeded.2.For the displacement reaction, by investigation the distance changes between main atoms along reaction coordinates, it is found that the elimination of HBr and the displacement reaction of hydroxy are synchronous. Similarly, the elimination reaction of HBr and ring closing reaction of oxygen are synergistic reaction in the epoxidation reaction. Someone defined the “effective reaction region” as a region of the breaking of old bonds and the formation of new bonds. This region is limited on the MEP where the geometrical structure of reaction molecules would change mightily. On the basis of these, it can be concluded that the hydrogen in the elimination of HBr comes from hydroxy.3.By discussing the changes of vibrational modes for the reactions, it can be found that there exists a special vibrational mode, which is called “reactive vibrational mode” and is relevant to the breaking and formation of covalent bond. The imaginary vibration model of transition state is studied chiefly, and points to reactant and product, and illuminates that stationary points locate the right reaction channel. On the basis of <WP=7>frequencies, IR Vibration spectra of reactants and products along reaction paths have been obtained. The results of calculation in theory are in good agreement with structures of reactants and products.4.Laplacian of the electronic charge density at bond critical point along reaction coordinates and isoline of Laplacian of electronic charge density in stationary points are studied by topological theory of electron density. The results show the position and the time of both the breaking of old bonds and the formation of new bonds in the reactions clearly, and explain the title reaction mechanisms. Furthermore, the results testify what the guess which author made was right.

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