Most industrial processes involve formation of new substances from a given set of starting materials and the knowledge of the reaction mechanism involved may make it possible to choose reaction conditions that favour maximum production of the desired end products and minimum production of the undesired end products. But how do these reactions proceed in explaining the end products?
Many reactions proceed in elementary steps in which particals collide to form intermediate products which are then converted by further reactions to form the final products. Each elementary step would have a hypothetical species which is too short lived to be detected using instruments. This species is called an activated complex or the transition state. It is the transition states that involve the breaking of the chemical bonds and the reforming of other bonds to form the end product molecules. This process of bond breaking and bond formation is so fast that transition states have very short half lives.
However these intermediate steps proceed at varing rates; some are pretty fast while some are rather slow. The rate determining step is the slowest intermediate step. It has the greatest effect on the overall rate of the reaction. Providing optimal conditions to this intermediate step would increase the overall rate of the reaction, and this way the overall cost of production is minimised.
Optimal conditions are environmental factors that influence the rate of the reaction such as providing optimal temperature and pressure and other physical factors that influence the reaction.
Reaction mechanism have been enormously useful in organic chemical reactions and it gives the chemist a degree of control over the reaction process.