The Theoretical Studies On Aromaticity Of Monocyclic Borazine Compounds

The aromaticity is an important parameter used frequently as a reactivity measure of many organic and inorganic molecules with delocalized (4n+2) n electrons in cyclic systems. It has attracted much attention on theory and experiment over the half past century. The previous results show that the C_nH^m_n and (BCO)^m_n (n=3-6, m=-1 +2) with (4n+2) Ï€ electrons, as well as C5XH5 (X=O and S) have aromaticity. In this dissertation, the geometries, vibrational frequencies and aromaticity of four series of monocyclic borazine compounds which are isoelectrons system of the above molecules have been investigated using ab initio and density functional theory (DFT), and the main contents are arranged as follows.In chapter 1, the development of the conception of aromaticity are presented and the theoretical methods used in this work, Hartree Fock self consistent field (HF-SCF), MP2 and density functional theory, are described in chapter 2.In the following two chapters, the structures and frontier molecular orbitals and nucleus-independent chemical shift (NICS) of five kinds of monocyclic ring borazine compounds (B₂NH²⁺, BN₂H²⁺₃, B₂N₂H²⁺₄, B₂N₃H₅, B₃N₃H₆) and the halogenating derivatizations B_nN_mH_mX_n (n=2³, m=2³, X=H, F, Cl, Br) are calculated at the HF/6-311+G^** and B3LYP/6-311+G^** level. Moreover, the total energies and the aromatic stabilization energy are calculated by B3LYP/6-311+G^** and MP2/6-311+G^** methods. In addition, the Natural bond orbital (NBO) analysis on B-N bonds of five and six-membered rings are obtained at B3LYP/6-31G^** level. The relationship between the aromaticity and the stability of the B_nN_mH_mX_n compounds are investigated. The results show that that both monocyclic ring borazine and halogenating derivatizations are aromatic compounds.In chapter 5, the structures and frontier molecular orbitals and the NICS curves of five kinds of the monocyclic ring borazine B_n(N₂)^m_n (n=3⁷,m=-1⁺2) are calculated at the HF/6-311+G^** and B3LYP/6-311+G^** level. The calculational results indicate such series of compounds are stable and have aromaticity.