Theoretical Study Of Non-covalent Bond Interactions Involved With Fulvene Derivatives

In this dissertation,fulvene,an important organic compound,is chosen to study the formation of hydrogen,halogen,pnicogen,chalcogen,and tetrel bonds of its derivatives by means of theoretical methods.The main contents are summarized as follows:The tetrel bond formed between 6-OTX₃-fulvene?T=C,Si,Ge;X=H,F?and NH₃is studied.By comparing with HOTX₃ and PhOTX₃,the ability of 6-OTX₃-fulvene forming a tetrel bond is explored,and the influence of substituents on the formation of a tetrel bond is investigated,in order to find a method to enhance a tetrel bond.In addition,the effect of the tetrel bond formation on the aromaticity of the fulvene ring is also studied.The results shows that,compared with HOTX₃ and PhOTX₃,the tetrel bond formed by fulvene derivatives is stronger,indicating that–OTX₃ connected to the fulvene ring is a good electron acceptor.For–TH₃,the tetrel bond is stronger in a pattern of Si>Ge>C,while for–TF₃,the tetrel bond becomes stronger in sequence of Ge>Si>C.This is due to the large deformation energy caused by the fluorine substitution.The tetrel bond can be enhanced by replacing the four hydrogens on the fulene ring with four cyano groups.No tetrel bond occurs for the–CF₃ group,but it can form a tetrel bond when there are four–CN substituents on the fulvene ring.The formation of a tetrel bond can increase the aromaticity of the fulvene ring.Quantum chemical calculations are applied to complexes of 6-OX-fulvene?X=H,Cl,Br,I?with ZH₃/H₂Y?Z=N,P,As,Sb;Y=O,S,Se,Te?to study the competition between the hydrogen bond and the halogen bond.The result shows that H-bond weakens as the base atom grows in size and the associated negative electrostatic potential on the Lewis base atom diminishes.The pattern for the halogen bonds is more complicated.In most cases,the halogen bond is stronger for the heavier halogen atom,and pnicogen electron donors are more strongly bound than chalcogen.The strength of the halogen bond appears in the order of O<S<Se<Te with chalcogen atoms,but the change of phosphorus donors is more ambiguous.In terms of competition,most of the halogen bonds formed with phosphorus donors are stronger than their corresponding hydrogen bonds,but there is no such clear pattern for chalcogen donors.O atoms tend to form hydrogen bonds,while Te atoms are more likely to form halogen bonds.For S and Se,the strongest I-bond is formed,followed by Br,H,and Cl-bond.The pnicogen,chalcogen,and halogen bonds formed between 6-OXF₂-fulvene?X=As,Sb,Se,Te,Br,and I?and three nitrogen-containing bases?FCN,HCN,and NH₃?are compared.By comparison,for each nitrogen base,the halogen bond formed is the strongest,followed by the pnicogen bond,and chalcogen bond is the weakest.For each type of bond,it becomes stronger in the pattern of FCN<HCN<NH₃.Both FCN and HCN engage in a bond with a comparable strength and the interaction energies of most bonds are less than-6 kcal/mol.However,the strongest base NH₃ forms a much stable complex,particularly for the halogen bond with the interaction energy up to-18 kcal/mol.For the same type of a noncovalent bond,its strength increases as the mass of the central X atom increases.These bonds are different in strength,but all of them are dominated by electrostatic interaction,and polarization contribution is important for the stronger interaction.The presence of these bonds would cause a change in the geometries of6-OXF₂-fulvene,particulary for the halogen bond formed by NH₃,where the F-X-F arrangement is almost vertical to the fulvene ring.