Ozonolysis is a reaction where an alkene is cleaved by ozone (O₃) to form carbonyl compounds (aldehydes or ketones). The process involves:

Step 1: Ozone adds to the double bond to form an ozonide.

Step 2: The ozonide is reduced (e.g., with Zn/H₂O) to give carbonyl products.

To find the original alkene from the products, reverse the process: combine the carbonyl carbons with a double bond. For product (a) $CH {CH}_{3} CHO$ and (b) $O = CH - CH = O$ , identify the carbon atoms that were part of the double bond. The carbonyl carbon in each product was originally one end of the double bond.

For (a) CH₃CH=O, the carbonyl carbon is from one end. For (b) O=CH-CH=O, both carbons are carbonyls, indicating it came from a double bond between them. Reconstructing: if CH₃CH=O comes from one end, and O=CH-CH=O from the other, the original alkene must be CH₃-CH=CH-CH=O. But O=CH-CH=O is glyoxal, which suggests a symmetric molecule. Actually, combining: the carbon of CH₃CHO (from the aldehyde) and one carbon of O=CH-CH=O (say the left carbon) were connected by a double bond. So the alkene is CH₃-CH=CH-CH=O. However, ozonolysis of this would give CH₃CHO and O=CH-CHO, which matches (a) and (b). So the reactant is CH₃CH=CHCHO.

Now, looking at the options, the correct structure is the one with CH₃-CH=CH-CHO. This is option 4: , which is CH₃-CH=CH-CHO.

Related Topics: Ozonolysis is part of alkene reactions. Understanding the cleavage helps in deducing structures.

Formulae: General ozonolysis: R₁R₂C=CR₃R₄ → R₁R₂C=O + O=CR₃R₄ after reduction.