Chapter 19: Aldehydes and Ketones

The chapter establishes the structural differences between aldehydes, which contain a carbonyl group bonded to at least one hydrogen atom, and ketones, which have the carbonyl carbon bonded to two alkyl or aryl groups. Students learn systematic nomenclature for both functional groups and explore how their physical properties, including boiling points and solubility, relate to the polarity of the carbonyl bond and opportunities for hydrogen bonding. The electrophilic nature of the carbonyl carbon is emphasized through resonance structures that illustrate charge distribution and reactivity patterns. A central theme involves nucleophilic addition reactions, where nucleophiles attack the electron-deficient carbonyl carbon, followed by protonation of the resulting alkoxide intermediate. The chapter details important addition reactions including hydration to form geminal diols, cyanohydrin formation through the addition of hydrogen cyanide, and imine or enamine synthesis via reactions with amines. Reduction mechanisms using reagents like sodium borohydride and lithium aluminum hydride are thoroughly explored, showing how these reactions convert carbonyls to primary or secondary alcohols. The chapter also addresses oxidation pathways that selectively target aldehydes while leaving ketones intact, particularly using chromium-based oxidizing agents. Aldol condensation reactions and their mechanistic pathways receive attention as key carbon-carbon bond-forming processes. Finally, students learn how to strategically employ aldehydes and ketones in multistep synthesis problems, recognizing them as versatile synthetic handles for constructing complex organic molecules.