How the Mechanism for Nucleophilic Addition-Elimination Was Confirmed

We have seen that nucleophilic addition-elimination reactions take place by a mechanism in which a tetrahedral intermediate is formed and subsequently collapses. The tetrahedral intermediate, however, is too unstable to be isolated. How, then, do we know that it is formed How do we know that the reaction doesn t take place by a one-step direct-displacement mechanism (similar to the mechanism for an Sn2 reaction) in which the incoming nucleophile attacks the carbonyl carbon and displaces the leaving group—a mechanism that does not break the rr bond and so does not form a tetrahedral intermediate  

To answer this question, Myron Bender investigated the hydroxide-ion-promoted hydrolysis of ethyl benzoate after first labeling the carbonyl oxygen of ethyl benzoate with an isotope 

CHAPTER 16 Reactions of Carboxylic Acids and Carboxylic Acid Derivatives 

When butanoic acid and 0-labeled methanol react under acidic conditions, what compounds will be labeled when the reaction has reached equilibrium  

Kursanov, a Russian chemist, proved that the bond that is broken in the hydroxide-ion-promoted hydrolysis of an ester is the acyl C—O bond, rather than the alkyl C—O bond, by studying the hydrolysis of the following ester under basic conditions  

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