Study On Molecular Face Theory Of Five-Membered Heterocyclic Compounds And Their Derivatives

Molecular face theory(MFT)is used to characterize the size and properties of the molecule by adhering the electron density on the molecular intrinsic characteristic contour(MICC).This thesis investigates electronic contour density,volume and surface area,single electron potential barrier of chemical bond(Dpb),single electron potential barrier of ring point(Dpr)and uniformity of electron density(ED)of 64 five-membered heterocyclic compounds and 24 derivatives of furan and pyrrole by the molecular face theory.And the relationships between the Dpb and strength of chemical bond,Dpr and molecular polarizability,and ED and aromaticity are discussed.(1)The MP2/6-311++G(3df,3pd)level is used to optimize 64 five-membered heterocyclic compounds,and the polarizability of these molecules are calculated at same level.The first ionization energies of 64 molecules are calculated at the level of MP2/6-31G.We use MELD program package and our own program to calculate the potential acting on an electron within these molecules and their volumes and surfaces using molecular face model and electron density model at CISD/3-21+G(d,p)level.Matlab is used to display the molecular face.Based on the potential acting on an electron within a molecule(PAEM),we discuss the relationships between the Dpb and strength of chemical bond,Dpr and molecular polarizability,ED and aromaticity.It can be obtained that Dpb can characterize the strength of chemical bond,Dpr can characterize the molecular deformation and ED can characterize the molecular aromaticity.In order to search for rules,we also compare ED with other quantitative descriptors of aromaticity and find the changes of molecular properties with the number of the substituted atom.(2)Based on the structure of furan and pyrrole,we can obtain 24 derivatives with eight different substituents(including electron withdrawing groups and electron donating groups)replace H atom at different site.These derivatives are optimized at MP2/6-311++G(3df,3pd)level,and the first ionization energies are calculated at the level of MP2/6-31G.Through calculating the potential acting on an electron at CISD/3-21+G(d,p)level by MELD program package and our own program,we obtain Dpb of same chemical bond of different molecules and Dpr at ring point.The changes of the first ionization energy,Dpb and Dpr with the substituents are also discussed in this paper.Through the analysis of molecular faces and properties of 64 five-membered heterocyclic compounds and 24 derivatives,it can be obtained that the rules of five-membered heterocyclic compounds with the number of heteroatom and the substituents.It can provide a theoretical basis to more explore the properties of five-membered heterocyclic compounds in near future.