Preparation of Aldehydes and Ketones from Alcohols, Alkenes, and Alkynes

Mild oxidizing agents like pyridinium chlorochromate convert primary alcohols to aldehydes without over-oxidation. Strong oxidizing agents cause the aldehyde to be further oxidized to a carboxylic acid. Weaker oxidants such as Swern and Dess–Martin oxidations also effectively produce aldehydes from primary alcohols, making oxidizing agent selection critical for controlling product formation.

Secondary alcohols form ketones through oxidation because the carbon bearing the hydroxyl group is bonded to two alkyl groups. This structural constraint prevents further oxidation beyond the ketone stage. Both mild and strong oxidants yield ketones from secondary alcohols, making the oxidizing agent strength irrelevant for this conversion.

Monosubstituted alkenes yield formaldehyde and a substituted aldehyde through ozonolysis. Disubstituted alkenes produce either two aldehydes (1,2-disubstituted) or formaldehyde plus a ketone (1,1-disubstituted). Trisubstituted alkenes give mixtures of aldehydes and ketones, while tetrasubstituted alkenes produce only ketones. Reductive workup ensures clean product formation.

Terminal alkynes undergo hydroboration-oxidation via anti-Markovnikov addition to form aldehydes as the primary product. Internal alkynes follow the same anti-Markovnikov pathway but yield ketones instead. This regioselectivity difference makes hydroboration-oxidation a predictable method for synthesizing specific carbonyl compounds from alkynes.

Acid-catalyzed hydration follows Markovnikov's addition rule, producing ketones from both terminal and internal alkynes. Hydroboration-oxidation follows anti-Markovnikov addition, yielding aldehydes from terminal alkynes and ketones from internal alkynes. The reaction conditions and mechanism determine which regioselectivity pathway dominates the transformation.

Ozonolysis cleaves the carbon-carbon double bond, converting it into carbonyl groups with predictable products based on alkene substitution. The nucleophilic addition to the carbonyl group mechanism allows controlled synthesis of aldehydes and ketones. Reductive workup ensures clean product formation without further oxidation or unwanted side reactions.

Primary alcohols are the most commonly used substrates because they readily form aldehydes under mild oxidation conditions. Secondary alcohols also serve as important substrates, consistently producing ketones regardless of oxidizing agent strength. The choice between primary and secondary alcohols depends on whether an aldehyde or ketone product is desired for downstream synthesis.