Enzymatic effects Claisen reaction

A large number of theoretical studies have accompanied experiments aimed at elucidating the mechanism of pericyclic reactions and predicting new processes. Given the enormous amount of theoretical works performed on this area, we will focus mainly on the Diels-Alder reaction as a prototype of these processes. Our goal is not to cover all aspects, but instead to show the high potential and usefulness of theoretical methods to interpret and rationalize the most important experimental aspects reactivity, mechanism, catalysis, and solvent effects. Solvent effects are also considered for the Claisen reaction, which is another peryciclic reaction that is dramatically accelerated by the solvent and is involved in important enzymatic processes. This has allowed us to illustrate the computational advances made in solvent and enzymatic effects. 

PROBLEM 20.45 We saw on page 1063 that chorismate undergoes a [3,3] sigmatropic shift (Claisen rearrangement) to prephenate catalyzed by the enzyme chorismate mutase. This enzyme-catalyzed reaction occurs more than 1 million times faster than the corresponding nonenzymatic reaction. How does the enzyme effect rate enhancement Both enzymatic and nonenzymatic reactions proceed through a chairlike transition state. However, the predominant conformer of chorismate in solution, as determined by H NMR spectroscopy, is the pseudodiequatorial conformer 2, which cannot undergo the reaction. 

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