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Collection of research reports best university in 2007 honored the author: 12. Truong Van Nam, Nguyen Xuan Dung, study the effect of substituents on the properties of aniline by approximate methods AM1 quantum . Quantum mechanics is one of the fundamental theory of physics. Quantum mechanics is an extension and supplement of Newtonian mechanics (also known as classical mechanics). It is the basis of many other disciplines of physics and chemistry as solid state physics, chemistry quantum particle physics. The concept of quantum to only some physical quantities such as energy (see Figure 1) is not continuous but discrete | ĐẠI HỌC VINH TẠP CHÍ KHQA HỌC TẬP XXXVI số 1A-2007 STUDyiNG SUBSTITUENT EFFECTS ON THE PROPERTIES OF ANILINE WITH APPROXIMATE quantum CHEmiSTRy method AM1 TRUQNG VAN NAM a NGUYEN XUAN DUNG a Abstract. Substituents effects on the properties of aniline were studied by approximate quantum chemical methods using HyperChem software 7.52 latest version . AM1 method has been used to optimize geometry and calculate some properties of molecules. The results show that substituents on the phenyl ring alter the bond length C-N d C-N charge on atom N of amino group QN dipole moment p and the pKa of compounds. There is a good correlation between these properties and Hammett Ơ constants which traditionally have been used to characterize quantitatively the substituent electronic effect except for d C-N QN of meta substituted compounds. I. Introduction The influence of substituents on physical and chemical properties of compounds has attracted much interest in chemistry. Generally substituents change reactivities conformations equilibrium relationships spectra and thermal properties of the substituted compounds. Aniline is an interesting object to study the influence of substituents. Aniline molecule was studied well 1-5 . On the basis of resonance theory electron -withdrawing constituents especially at the para position should favor quinoid resonance structures which are more planar than aniline itself decreasing both negative charge on N atom and the C-N bond length. Conversely electron-donating substituents should favor Kekulé-type structures with more nearly tetrahedral conformations at the nitrogen atom and increase charge on N atom and d C-N bond length 6 . N H H N H H N H H N H H N N X X X X HyperChem is a sophisticated molecular modeling environment that is known for its quality flexibility and ease of use. It unites 3D visualization and animation with quantum chemical calculations molecular mechanics and dynamics 7 . Nhận bài ngày 07 8 2006. Sửa chữa xong 05 10 2006. 77 .
