| Budget Amount *help |
¥7,600,000 (Direct Cost: ¥7,600,000)
Fiscal Year 2003: ¥1,300,000 (Direct Cost: ¥1,300,000)
Fiscal Year 2002: ¥1,800,000 (Direct Cost: ¥1,800,000)
Fiscal Year 2001: ¥4,500,000 (Direct Cost: ¥4,500,000)
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| Research Abstract |
In order to clarify dynamic routes of liquid-phase organic bimolecular reactions, we studied kinetic effects of viscosity in the following "slow" thermal reactions. 1.Fading of merocyanines formed from a spironaphthoxazine and a spironaphthopyran. 2.Fading of a colored open-ring species formed from substituted chromenes. 3.Fading of 1,1-diarylalkyl cations in alcohols. 4.Prototropic tautomerization of an enamine formed from 2-(2,4-dinitrobenzyl)pyridine.
As reaction media, we adopted three viscous liquids, 2-methylpentane-2,4-diol, glycerol triacetate, and 2,4-dicyclohexyl-2-methylpentane. The viscosity was manipulated over a range of 0.1 -10^6 Ps s by externally applying high pressures. Since the viscosity dependence thus observed inevitably contains pressure dependence of the free energy of activation, we also studied pressure dependence of the same reaction in less viscous solvents with a similar molecular structure and a polarity, i.e., ethanol, methyl acetate and methylcyclohexane,
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respectively. By comparing the results in viscous and nonviscous media, we successfully isolated viscosity dependence of the reaction rate from the total pressure dependence both in unimolecular and bimolecular processes. From these experiments, we reachedfollowing conclusions. 1)Solvent molecules have to be reorganized prior to chemical structural changes of the reactant and, therefore, one unified reaction coordinate assumed by Kramers could not satisfactorily describe dynamic routes of solution reactions. Solvent reorganizations and chemical structural changes had to be described by two mutually independent medium and chemical coordinate. 2)The extent of coupling of the two reaction coordinates was highly dependent on the reaction system. 3)Solvent rearrangements predominantly took place around a particular atomic group of the reactant. In other words, when atomic groups move along the reaction coordinate, a particular atomic group changed its position in a solvation shell while the rest of the molecule stayed more or less in the same position.
In summary, we obtained experimental evidence for 1)asynchronism of solvent rearrangements and chemical transformations and 2)spacial preference of solvent rearrangements around the reactant. Less
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