Conclusion

In this second chapter on aldehydes and ketones, we’ve taken a look at the important resonance
structures that the carbonyl of aldehydes and ketones allows. The high electronegativity of the
oxygen atom in a carbonyl not only makes the carbonyl carbon electrophilic, but also weakens the
C–H bonds on α-carbons. Deprotonation of this α-carbon results in an enolate, a nucleophilic
version of carbonyl-containing compounds. Thus, while the carbonyl carbon dictates the
electrophilic chemistry of carbonyls, it is the α-carbon, along with its acidic hydrogens, that dictates
the nucleophilic chemistry of carbonyls.

Aldehydes and ketones are not the only carbonyl-containing compounds, of course. Carboxylic acids
and their derivatives, including esters, anhydrides, and amides, also have chemistry controlled by a
carbonyl. But there is one critical difference between aldehydes and ketones, and carboxylic acids
and their derivatives: the absence or presence of a leaving group. While aldehydes and ketones lack
leaving groups, carboxylic acids and carboxylic acid derivatives have leaving groups with varying
degrees of stability. Over the next two chapters, we’ll explore the chemistry of these interesting
groups of compounds.