Theoretical Research Of Intermolecular Non-covalent Interaction:Tetrel Bonding And Plasticizer Migration

Non-covalent interaction between molecules including hydrogen bonding,halogen bonding,tetrel bonding,such as in medicinal chemistry,physical chemistry,biochemistry and supramolecular self-assembly,and other fields has played a very important role,given the many physical,chemical and life phenomenon is closely related,non-covalent interaction has become the current hot research.Two kinds of weak interactions have been studied in this paper.One is the polycentric π-hole tetrel bond,and the other exists in the complex system formed by plasticizer and analogue.In SN2 reaction,the three-center five-electron π-hole tetrel bonding acts as a transition state,and the study of the basic physical and chemical properties of the π-hole tetrel bond is very important for the study of the basic reaction mechanism.At present,the research on π-hole tetrel bond is still in the initial stage,and the detailed study on the influencing factors of π-hole tetrel bond is conducive to a better understanding of the unique behavior of transition states in SN2 reaction,so as to effectively control the effective application of π-hole tetrel bond in various fields.Plasticizer,one of PVC additives,acts as a lubricant in the polymer chain.Nowadays,considering the harm caused by traditional plasticizers to human health and natural environment,the study of plasticizer migration in various substances can provide a theoretical basis for the solution of the above problems.And considering the disadvantages of traditional plasticizers,the study of new plasticizers has become the current research hotspot.The paper is mainly divided into the following four chapters:In chapter one,the research background and significance of this thesis were mainly introduced.Including the classification,application and research significance of intermolecular interaction.Then,the significance and background of the non-covalent interaction-tetrel bond and plasticizer migration studied in this paper are introduced,and according to the current research status of the subject,the content and purpose of this study are determined.In chapter two,the calculation methods,basic theories and analysis methods used in this paper are introduced,including quantum chemistry,density functional(DFT)theory,natural bond orbital(NBO)theory,molecule in atom(AIM)theory,ab initio method,compact binding method,energy decomposition analysis,molecular surface electrostatic potential analysis and non-covalent interaction analysis.In chapter three,ab initio calculation were performed to study the multicenter π-hole tetrel bonding with carbocation as the electron acceptor and two NH3 as electron donor.we found that the π-hole tetrel bonding in the complexes is three-center five-electron electronic structure,instead of three-center four-electron one.The multicenterπ-hole tetrel bonding is favorable only with specific ligands to centered-carbenium carbon,such as conjugative cyclic groups.The geometries of the carbocations with cyclic groups as ligands are in fan-like spiral shape with p orbital occupancy of the central C+close to le due to the remarkable delocalization effect in the carbocation.There is trivial negative synergistic effect in these three-center five-electron π-hole tetrel bonding due to the subtle balance between the electron-donating effect of nitrogen lone pair of NH3 and the multicenter delocalization electronic effect.We found that the electrostatic interaction plays crucial role in the stability of the three-center five-electron π-hole tetrel bonding.Different solvent polarity has little effect on the strength of three-center five-electron π-hole tetrel bond.In chapter four,the charge-tight-binding approximation based on self-consistent density functional theory of molecular dynamics method is used to study the migration of traditional plasticizers DEHP.By simulating the dynamic process of the interaction between the plasticizer molecule DEHP and three common food analogues and PVC,and comparing the binding energy of DEHP and each system,the migration trend of DEHP from PVC material to food analogues and the influence of the migration trend with the concentration of food analogues were explored.It was found that the type of contact and the concentration of contact had certain influence on the plasticizer migration.By studying the interaction between plasticizer and contact material,it is found that hydrogen bond and van der Waals force are the main interactions,and halogen bond also plays a certain role in the interaction.The purpose of this study is to provide theoretical basis for solving the problems caused by traditional plasticizers and developing new plasticizer molecules.