thanks The reaction is proposed to proceed according to the mechanism shown belo

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The reaction is proposed to proceed according to the mechanism shown below. The authors did the following experiment: In the presence of the catalyst, A was exposed to a mixture containing 5 equivalents of D and 5 equivalents of E. The authors then measured the rate of consumption of D and the rate of consumption of E. They got the KIE of 0.87. The authors interpreted this result as an indication that the rate limiting step of the reaction is the C-C bond forming step. Is this a correct interpretation of the result? Explain.

Explanation / Answer

If KIE value is less than 2, bond breaking wont happen in rate determining step.

Here rate determining step is the the attack of C=C-(OMe)(OSiR3) to C=O+, i.e. C-C bond forming reaction.

Here there is no bond cleavage hence the observed rate suggest that, the proposed mechanism is right only.

In case the bond is break in the rate determining step, then you will observe more KIE value (KIE>2).

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