Carbonyl group, addition reactions general characteristics

As a general rule, nucleophilic addition reactions are characteristic only of aldehydes and ketones, not of carboxylic acid derivatives. The reason for the difference is structural. As discussed previously in A Preview of Carbonyl Compounds and shown in Figure 19.14, the tetrahedral intermediate produced by addition of a nucleophile to a carboxylic acid derivative can eliminate a leaving group, leading to a net nucleophilic acyl substitution reaction. The tetrahedral intermediate... 

The characteristic reactions of aldehydes and ketones involve nude ophihc addition to the carbonyl group and are summarized m Table 17 5 Reagents of the type HY react according to the general equation... 

We commented earlier in this chapter that carboxylic acids are similar in some respects to both alcohols and ketones. Like alcohols, carboxylic acids can be deprotonated to give anions, which are good nucleophiles in Sn2 reao tions. Like ketones, carboxylic acids undergo attack by nucleophiles on the carbonyl group. In addition, carboxylic acids undergo other reactions characteristic neither of alcohols nor ketones. Figure 20.4 shows some of the general reactions of carboxylic acids. 

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