Methods of determining of reaction mechanism


• i) Identification of products: Any proposed mechanism for a given reaction must account for all the products and the relative amounts including minute side products if any. 


• ii) Detection of presence of intermediates: Many of the reactions involve intermediates. It has to be determined and identified and their presence have to be proved.


• iii) Study of catalysis: Mechanism of a reaction can be well understood if we come to know which substances act as catalysts and which substances inhibit the reaction and which do not have any influence.


• iv) Isotopic labelling: Use of isotopes in investigation of a mechanism is extensively used and may be very helpful in determining of the mechanism.


• v) Stereochemical evidence: Stereochemical out come of a reaction is helpful in deciding the mechanism of a reaction. e.g. SN1 and SN2 reaction can be distinguished based on the stereochemistry of the products formed.


• vi) Study of kinetics of reaction: Kinetic study is an essential aspect to be studied for supporting or proposing of a reaction.


Reactive intermediates in study of mechanism


• As we have seen intermediates are short living chemical species in organic reactions. They do exist or form during the process of overall reactions.


• There are many reactions for which it is necessary to propose the formation of intermediates based on the products, kinetics and other results.


• How can the existance of intermediates be proved in a reaction?


• There are several ways bywhich it may be done.For some reactions it is possible to isolate an intermediate by stopping reaction after a short time or by changing the reaction conditions which stabilize the postulated intermediate.


• In the Wittig reaction it is proposed that a betaine is formed during the reaction of an ylide with a carbonyl compound.