Bimolecular Reactions in the Solution Phase

Solvation takes place within 100-1000 fs. Reactions in the solution phase take place in a cage of solvent molecules. Bimolecular reactions in the solvent cage take place within several hundred femtoseconds, whereas colhsions in the gas phase take place in the order of picoseconds. In the solvent cage, molecules A and B collide with each other, and a successful collision leads to reaction to give product P. Excess energy from P is transferred to solvent molecules by the subsequent collision with solvent molecules. Therefore, one of the most important roles of the solvent is removal of heat generated in the reaction. In the solution phase, the rate of a chemical reaction is determined by the activation energy. This is mostly 

9 Fast Chemical Synthesis Inspired by Reaction Dynamics 

As described above, the progress of reaction dynamics showed how chemical reactions take place. Is it possible to apply the methods and techniques of reaction dynamics to chemical synthesis If we can activate all the molecules at once, the chemical reaction takes place and finishes within several hundred femtoseconds. If it is possible, synthesis can be complete within several hundred femtoseconds. Such a method leads to the ultimate acceleration of chemical synthesis. 

However, the requirements for chemical synthesis and those for reaction dynamics studies are different. In chemical dynamics studies, we activate starting molecules at once and observe the subsequent reaction. Coherency of the activation is important but the number of activated molecules is not so important as long as we can observe them. In chemical synthesis, however, the number of molecules which participate in the reaction is much more important because it directly relates to productivity. Therefore, all the molecules in the system should be activated, but coherency of the activation is less important. We usually synthesize compounds on the 10 -10°mol scale in laboratories and on the 10 -10 mol scale in chemical plants. Such amounts of molecules should be activated in a very short period for time-efficient chemical synthesis. 

It is also worth noting that many reactions consist of two or more reaction components in chemical synthesis, because they are useful to construct molecules however, most reaction dynamics studies deal with unimolecular reactions because it is difficult to arrange coherent collisions of two molecules. In time-efficient chemical synthesis, it is also important to know how to achieve collisions of two molecules in a very short period to accelerate bimolecular reactions. 

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