Theoretical Studies Of Ruthenium Clusters And Some Organic Reactions

This dissertation contains two projects. The first project is a theoretical study of ruthenium clusters and the second project is a theoretical study of some organic reactions. A systematic investigation of ruthenium clusters was carried out using density functional theory with a plane wave basis set in the first project. The results have shown that the simple cubic structure is the most stable structure in the small ruthenium clusters. Analysis suggests that the simple cubic structure could be the most stable structure for clusters of up to 40 atoms, the icosahedron is the most stable structure for clusters of 40-147 atoms, and finally the cubo-octahedron, that is, the bulk structure, becomes the most stable structure for clusters of more than 147 atoms. A strong trend of trimer formation was found in linear ruthenium clusters. All the clusters investigated here have small HOMO-LUMO band gaps, which indicates that they are good electrical conductors. They are also ferromagnetic with large magnetic moments. A quantitative correlation was provided between the energetic, electronic, and magnetic properties of ruthenium clusters and the cluster structure and size. Analysis of the calculated binding energies indicates that the atoms in similar bonding environments have similar binding energies. On the basis of this analysis, estimations were made on the binding energies of planar and simple cubic ruthenium clusters. The estimated binding energies agree well with the density functional theory results. The second project is divided into three parts. In the first part the reaction mechanism and regioselectivity of spiro-isoxazoline derivatives synthesized by an intermolecular 1,3-dipolar cycloaddition reaction between 2,6-dichlorobenzonitrile oxide and 3-(4-chlorobenzylidene)-dihydrofuran-2-one were studied using density functional theory and ab initio theory. Two possible reaction channels, which are related to the formation of isoxazoline-5-spiro-cyclic (Channel 1) and isoxazoline-4-spiro-cyclic (Channel 2) are investigated using natural bond orbital analysis, geometrical parameters analysis, energy analysis and frontier molecular orbital analysis. The energy analysis shows that both the activation energy and reaction energy for Channel 2 are higher than those for Channel 1. The larger activation energy prevents the formation of isoxazoline-4-spiro-cyclic. Therefore, isoxazoline-5-spiro-cyclic is formed as the energetically favored product. The FMO analysis shows that the regioselectivity of this reaction is controlled by the LUMOdipole–HOMOdipolarophile interaction, and the reaction proceeds via Channel 1 which agrees with the experimental results. The natural bond order analysis shows the reaction follows a concerted mechanism with two bonds formed at about the same time. The second part investigated the structure of CH3O and CH2OH radical and their intramolecular and intermolecular isomerization reaction. The study found that reaction barrier of intramolecular isomerization is higher than that of intermolecular isomerization and intermolecular isomerization can produce in room temperature. A cyclical transition state was found which was not reported in literature.The third part investigated the structure and vibration frequencies 3-benzyloxy-2-nitro-pyridine. The NO2 group rotate out of the pyridine plane was explained by calculated the rotating barrier. The IR spectrum of 3-benzyloxy-2-nitro-pyridine was studied by vibration frequencies calculation. Some other substituted 2-nitro-pyridine were investigated and the conjugation effects, steric hindrance and hydrogen bond are explained.