Separation and Estimation of Rate Constants

As outlined above, temperature analysis may be successfully performed if the unimolecular and bimolecular rate constants are known if the rate constants are known, and if we choose a standard state, a free energy profile can be drawn. Thus, the above thermodynamic analysis for a monosubstrate reaction shows that the meaningful application of a k/T) against /T plots requires that the individual uni- and bimolecular microscopic rate constants be separated. 

A number of procedures have been used to separate rate constants in enzyme mechanisms. We shall mention only briefly (a) rapid mixing techniques that can separate and measure almost all individual rate constants, (b) studies with alternative substrates that can provide information about the relative magnitude of some rate constants, and (c) work with alternative nucleophiles that can help to 

The second-order rate constant is a composite value and the plot of ln(/co/T) against /T will not necessarily apply to this constant directly. There are, however, two special cases under which this composite constant will obey the normal temperature behavior, as follows  

Since k varies exponentially with temperature according to 

In other words, the plot of n(k/T) against 1/T should apply to this composite constant hkjka, but the free energy of activation does not correspond to a  

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