2005 Fiscal Year Final Research Report Summary
Solvent effects on the dimerization equilibria of nitrogen dioxide
| Project/Area Number |
16540367
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Biophysics/Chemical physics
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| Research Institution | Kyoto University |
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Principal Investigator |
YOSHIMURA Yosuke Kyoto University, graduate school of science, assistant professor, 大学院・理学研究科, 助手 (10192428)
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| Project Period (FY) |
2004 – 2005
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| Keywords | chemical equilibrium / statistical thermodynamics / fluid / solvent effect / computer experiment |
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| Research Abstract |
Dimerization equilibrium constants of nitrogen dioxide were determined in several mixed solvent systems, such as cyclohexane-dioxane, by means of light absorption. The dimerization constant in cyclohexane-dioxane increases monotonically with the increase in mole fraction of dioxane, while the increasing rate is larger at low mole fractions. The partial molar volume of dinitrogen tetroxide in dioxane is smaller than that in cyclohexane, in which the dimerization constant is smaller. The theoretical calculations were also made on the basis of the simplest interaction model in which a pair of spherical molecules are dimerized in a two-components fluid mixture composed of spherical molecules. Theoretical calculation gave non-monotonical change of the dimerization constant with the change in the solvent composition. The disagreement between the experiment and the theory was ascribed to the multibody interaction between solute-solute-solvent ; the change in the electron distribution of the molecule with the bond formation between nitrogen dioxide brings about larger solute-solvent interaction in the dimer molecule than that given by the pair additive interaction between the monomer molecule and the solvent. A simple extension of the model system to the multibody potential system gives qualitatively the same behavior as found in the experiments. Contribution of the solvophobic interaction was also studied for a model system composed of hard needles and the solvent molecules interacting with the square-well potential. The solvophobic effect is not large. However, the solvophobic effect can be repulsive as well as attractive, depending on the molecular dimension and the configuration of the monomer molecules.
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