A New Method to Analyze the Intrinsic Energy of the Partial Structure in Conjugated Hydrocarbons.
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概要
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It is very important to analyze partial structures to understand stability and chemical reactivity of a molecule. We have been studying about the benzene which has the structure of the most stable 4n+2π-electron system in conjugated hydrocarbons^<1-4>. The hexagon (6-membered ring), i. e. embedded benzene, in a molecule has various stability depending on the environment in a molecule. The stability of this local structure determines the whole stability of a molecule. We proposed a new method to calculate the intrinsic energy of the partial structure by using "extracted Hamiltonian" before^<1, 2>. In this paper, the extracted Hamiltonian is improved, and how to extract the energy of the partial structure in additive property is proposed. This method can be applied to any partial structures in a molecule. We particularly pay attention to the hexagon and the bond formation energy in the part of the hexagon is calculated. The concept of the "energy density" is introduced by using the theory of the propagator^<5-9>. We can estimate the contribution from the electrons propagated from the site to the bond formation energy in the hexagon. It becomes clear by calculating the energy density whether the bond formation in the hexagon is the contribution from the electrons in the hexagon or from the electrons outside the hexagon. This result is compared with "local aromaticity" introduced before^<10>. In this paper, a new concept of the "independence of the hexagon" is presented. This concept is very useful in the estimation of the stability of the hexagon. The energy density enables us to calculate the degree of the independence of the hexagon. The importance of the classical Kekule structure is explained by the evaluation of the independence of the hexagon.
- 高山自動車短期大学の論文
- 2005-01-31