Research On Topological Characteristics Of Electron Localization Function Of Two Typical SN2 Reaction

Chemical bonds and reactions are two central concepts of chemistry.Very recently,the topological analysis of Electron Localization Function（ELF）provided a very powerful tool to understand the nature of chemical bond through the definition of bonding basins of ELF.In this thesis,electron density integrals of electron density for ELF basins were carried out,and the change of the integrals of ELF basin along two typical SN2 reactions was analyzed.The nature and the quantitative electron transfer description of bond forming and breaking process were discussed.In chapter 1,a brief introduction of SN2 reaction and basic concept of topology of electron density and electron localization function were carried out.Chapter 2 gave the basic theoretical aspects used in this thesis,including quantum chemistry,transient state theory and quantum theory of atoms in molecules.In chapter 3,the IRC of Cl + CH₃Cl → ClCH₃ + Cl was calculated at B3LYP/6-31G*,and the topological analysis of electron density and electron localization functions for different geometry along the Intrinsic Reaction Coordinate（IRC）process was carried out with program package of GTA,which was established by our group.For each IRC geometry,the electron density integrals of ELF basins were calculated with GTA.By analyzing the integrals changes along the IRC,the nature and the quantitative electron transfer description of bond forming and breaking process were discussed.Results show that the breaking of C-Cl1 and forming of C-Cl3 occurs simultaneously,while the nature of breaking bond and forming bond are different — a covalent bond only formed（C-Cl3）after the a breaking of a covalent bond（C-Cl1）.The changes of electron density of ELF basins gave the quantitative electron transfer description of bond forming and breaking process: the electron of ELF Core basin（C（C）and C（Cl））barely involve in the bonding changes,the electron of ELF bonding basin of C-H（V（C,H））involve in the bonding changes slightly,while the bond formation and breakage always accompany with obvious changes of the electron of ELF Valence basin（V（Cl））.In chapter 4,the same calculations used in chapter 3 were carried out for SN2 typical reaction system of HOCH₃ + Br→ HO + CH₃ Br Results also show that the breakage of C-O and formation of C-Br occurs simultaneously,while the nature of breaking bond and forming bond are different — the C-Br covalent bond only formed after the breaking of the O-C covalent bond.The changes of electron density of ELF basins gave the quantitative electron transfer description of bond forming and breaking process: the electron of ELF Core basin（C（C）,C（O）and C（Br））barely involve in the bonding changes,the electron of ELF bonding basin of C-H and O-H（V（C,H）and V（O,H））involve in the bonding changes slightly,while the bond formation and breakage always accompany with obvious changes of the electron of ELF Valence basin of V（O）and V（Br）.