Studies On Process Of Reaction Of Bromine With Benzene

The quantum chemistry, whose theoretical foundation is the quantum mechanics and mainly tool is the computer, studies the relation of the microstructure and macroproperty of the substance and interprets the essence of the substance and chemical reaction. In this paper, we study the two questions by the procedure of Gaussian 98. 1 .The study on the process of bromine reaction of benzene The electrophilic substitution reaction of benzene molecular and bromine by the catalyzer is called the bromine reaction of benzene. We study the bromine substitutes hydrogen process on the benzene ring, using density functional theory at UB3LYP/6―31G(d) level, By optimizing the transition state and the intermediate product, we obtain the potential energy surface for energy change with reaction coordinate and get the stable structures of the transition state. The transition state is verified by the vibration frequency analysis, and the reaction pathway is examined by the IRC calculation. We also analyze the process of electron transfer. The calculation shows that a positive charge of Br+ transfers to H through the intermediate, [C6H6Br]+, then, it is released by proton. In fact, it is a process of electron transfer, and the distribution of electron cloud in the process has been changed. From the potential energy surface, we can see the process that the C6H6+Br+ changes to the [C6H6Br]+ is spontaneous and need no extra energy. Because the energy of C6H6+Br+ is higher than that of C6H5Br+H+, we judge that the added energy in the reaction process is to accelerate the FeBr3 to react with the Br2, obtaining the Br+ and at the same time to run up the reaction speed. The process of Br+ attacks the benzene ring is the slowest in the whole reaction, and the reaction time is mainly determined by it. But the process that H+ is released by the [C6H6Br]+ is very fast. We discuss this question with classical theory, for the mass of the Br+ is much larger than that of H+, its speed change resulted from the coulomb force of the negative background charge, is very slow in the reaction process. It cost so much time that it impacts the whole reaction speed. On the contrary, the attractive power felt by H+, which comes from Br, becomes bigger and bigger. It leaves off the positive ion intermediate very soon andproducts HBr. To the above structure, we calculate its single point energies at the MP4/6-31G(d) level and AM1 level, respectively. We give the figures of the potential energy of the three methods. From the figure, we find that the energy of MP4 is quite close to that of B3LYP, although the results of AM1 is far from them, the regulations of the three methods are qualitatively accordant. 2.The study on a new structure and its stability of C32 isomer The study has shown that C32 is one of the most stable car bon fullerene (n<60). The study on the superconduction of C32 is very active and it has become one of the hottest topics in rec -ent years. There are many isomers for 32-atom carbon clusters, inc luding fullerene structure and non-fullerene structure. The full erene structure is composed of pentagonal and hexagonal rings, and the non-fullerene structure contains other rings besides th em. We construct a new isomer of C32 with D2h symmetry and with no pentagons and hexagons. It is a quite unique structure. The calculation has been performed using RB3LYP method of Density Functional Theory (DFT) at the...