Theoretical Study on Hydrogen Interaction between 5-Fluorouracil and Glycine

The geometries,electronic structure,IR spectrum and other properties of hydrogen interaction between 5-fluorouracil and glycine were studied at the B3LYP/6-31＋G＊ level.Single point energy calculations were executed at the B3LYP/6-311＋＋G＊＊ and B3LYP/aug-cc-pvdz levels,and natural bond orbital （NBO） analysis was carried out at the B3LYP/6-31＋G＊ level.Finally,the hydrogen bonds were discussed via AIM electronic density topology analysis.

Study on the Intramolecular Hydrogen Bonds of Dibenzofurans, Xanthones and Anthraquinones with One or Two Positions Substituted by Hydroxyls

The thermodynamic properties of dibenzofurans （DFs）, xanthones （XTs） and an-thraquinones （AQs） with one and two positions substituted with hydroxyls in the ideal gas state at 298.15 K and 1.013×10^5 pa were calculated at the B3LYP/6-311G^＊ level using Gaussian 03 program. The isodesmic reactions were designed to calculate the standard free energy of formation （△fG^θ）. Three types of hydrogen bonds exist in the three kinds of chemicals and their bond energies were ascertained as 7-15, 15-23 and 49-58 kJ·mo1^-1 respectively by comparing the △fG^θ values. Electronic density topology analysis was applied to validate the strength of bond.

AIM Study on the Reaction of CH2SH Radical with Fluorine Atom

The reaction of CH2SH radical with fluorine atom was studied at the levels of B3LYP/6-311G（d,p） and MP2（Full）/6-311G（d,p）. The computational results show that the reaction has three channels and proceeds by the addition of fluorine atoms on carbon or sulfur sites of CH2SH, forming initial intermediates. The calculated results show that the channel, in which fluorine attaches to the carbon atom to form CH2S and HF, is the most likely reaction pathway. Topological analysis of electron density was carried out for the three channels. The change trends of the chemical bonds on the reaction paths were discussed. The energy transition states and the structure transition regions （states） of the three channels were found. The calculated results show that the structure transition regions are broad in unobvious exothermic reactions or unobvious endothermic reactions, and are narrow in obvious exothermic reactions or obvious endothermic reactions.

AIM Study on Reaction HNCX→HXCN （X=O, S and Se）

The reactions of HNCO to HOCN, HNCS to HSCN and HNCSe to HSeCN have been studied at MP2/6-311 ＋ ＋ G（2df, pd）//B3LYP/6-311 ＋ ＋G（2df, pd） level. Geometries of the reactants, transition states and products have been optimized and geometries of the transition states are reported for the first time. The reasons why HNCO and HNCS instead of HOCN and HSCN were easily detected have been explained. It was predicted that HNCSe will be more easily detected than HSeCN. The breakage and formation of the chemical bonds in the reactions have been discussed by the topological analysis method of electronic density. The calculated results show that there are two kinds of structure transition states （STS） in reactions studied.