General Aspects of Exchange Reactions

As there are a number of features which are common to all exchange reactions, it is of value to consider these in some detail before discussing the results which have been obtained for the exchange of individual hydrocarbons. Exchange reactions are a unique class of chemical reactions, and attention will be directed to the methods of interpretation of experimental data which are relevant to the study of exchange reactions and to the ways in which these may be classified. 

Let us consider the reaction between a typical hydrocarbon, C Hm, and D2. As a result of the exchange reaction, two kinds of equilibria will be established. There will firstly be an equilibrium distribution between the total amount of deuterium in the hydrocarbon and the total amount of deuterium in the hydrogen. Secondly, the relative amounts of the different isotopic species of hydrocarbon will be in equilibrium, and the same will apply to the different isotopic species of the hydrogen. In other words, the following interconversion equilibria for the hydrocarbon will be established, 

In those cases where equilibrium constants for reactions of this type have 

The values of the equilibrium constants for the reactions shown in Equation (1) calculated by classical theory correspond to combinations of terms in the appropriate binomial expansion and all the equilibrium constants are given by the general equation 

Equilibrium Percentages of Propanes using a Ratio of Deuterium Propane of 2 1 

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