Nucleophilic substitution at a carbonyl group

In these reactions (12-41-12-44), a carbonyl group is attacked by a hydroxide ion (or amide ion) giving an intermediate that undergoes cleavage to a carboxylic acid (or an amide). With respect to the leaving group, this is nucleophilic substitution at a carbonyl group and the mechanism is the tetrahedral one discussed in Chapter 10. 

Nucleophilic substitution at a carbonyl group (10.11) takes place by an addition-elimination mechanism (10.16) ... 

Click Mechanisms in Motion to view the Mechanism of Nucleophilic Substitution at a Carbonyl Group under Basic Conditions. 

Mechanism of nucleophilic substitution at a carbonyl group under basic conditions. 

To finish, we should just remind you of what to think about when you consider a nucleophilic substitution at a carbonyl group. 

This reaction is often called the iodoform reaction. Iodoform was an old name for tri-iodomethane, just as chloroform is still used for trichloromethane. It is one of the rare cases where nucleophilic substitution at a carbonyl group results in the cleavage of a C-C single bond. 

You might have been surprised that the intermediate in the aldol step of this reaction did not decompose. This intermediate could be described as a tetrahedral intermediate in a nucleophilic substitution at a carbonyl group (Chapter 12). Why then does it not break down in the usual... 

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