Elucidation of Reaction Mechanisms - Introduction / Products and Intermediates
Elucidation of Reaction Mechanisms in Organic Chemistry - Introduction
- Reaction mechanism
- The reaction mechanism of a chemical reaction is a step-by-step description of the course on which the starting products are converted into the products. The course is described on a molecular level and contains information about the position of all atoms and electrons of the reactants (including the solvent, etc.) at each point of the reaction course - the so-called reaction coordinate (RC) - and, thus, about all the shiftings and movements of electrons and atoms.
Practically speaking, it is virtually impossible to collect all this information about a particular reaction. In addition, there is no analytic method available by which the whole reaction course could be determined in one step.
Therefore, several different methods have to be applied in order to elucidate a reaction mechanism. Usually, only one part of the reaction course can be traced with each of these methods. When all the various pieces of the puzzle are then combined with each other, step-by-step, an overall picture of the reaction mechanism is acquired. However, due to the complexity of a detailed reaction course and the limited efficiency of the analytic methods, a reaction mechanism cannot be completely elucidated. Thus, a proposed mechanism always exhibits the character of a postulate and can be extended, altered or, in an extreme case, completely rebuilt as a result of additional investigations.
In most cases, the proposed mechanisms describe the actual reaction course well enough so that they are quite useful.
- For which purposes may the proposed mechanisms be used?
- Why is it critical for chemists that they possess keen knowledge of a reaction's mechanism?
- Why is the chemical equation, that contains the starting products, products and reagents, not sufficient?
Generally speaking, the aim of a chemist is ...
- to acquire the desired products of a chemical reaction in high-yield,
- to get the reaction to run as efficiently and rapidly as possible, while it can still be controlled,
- to minimize the consumption of energy and substance,
- to minimize any dangers for the immediate and further vicinity as well as the environmental pollution by waste products,
- and, if necessary, to predict and control the stereochemistry of the products.
Knowledge of the chemical equation is not enough for planning and carrying out a reaction in such a manner that all or at least most of these aims are achieved. Instead, a thorough knowledge of the reaction mechanism is mandatory, or at the very least extremely helpful, in planning and carrying out a reaction in a controlled manner.