What are the main products of ozonolysis of an alkene after reductive workup?

• A. Two aldehydes
• B. A ketone and an aldehyde
• C. Two carbonyl fragments (aldehydes/ketones); if terminal, one fragment is formaldehyde
• D. An alcohol and a ketone

Answer: (C)

Ozonolysis followed by reductive workup cleaves the C=C bond and furnishes two carbonyl-containing fragments. Each fragment is an aldehyde or a ketone depending on what the two carbons of the original double bond were attached to. If a carbon originally bears hydrogens (a terminal position), that fragment becomes an aldehyde; if a carbon bears two carbon substituents, that fragment becomes a ketone. When the double bond is at the end of the molecule, one fragment is formaldehyde because the terminal carbon is converted to H2C=O. The reductive workup steers the products toward carbonyls rather than oxidized acids, so alcohols or carboxylic acids are not formed. Therefore, the main products are two carbonyl fragments (aldehydes or ketones), with one fragment being formaldehyde if the original alkene is terminal.