Question

One mole of an alkene on ozonolysis gives a mixture of one mole pentan-3-one and one mole methanal. The alkene is

• A. 3-ethylbut-1-ene
• B. 2-methylpent-1-ene
• C. 2-ethylbut-1-ene
• D. 4-methylpent-2-ene
• E. 4-methylpent-1-ene

Hint:

Reverse ozonolysis is like solving a puzzle piece connection. Just erase the '=O' from both product molecules and connect the 'sticky ends' (the carbons) with a double bond. Always be careful to select the correct longest chain containing the double bond when naming the resulting structure.

Answer 1

The Correct Option is C

Step 1: Concept of Ozonolysis
Ozonolysis cleaves the double bond of an alkene to give carbonyl compounds.
To find the alkene, we reverse the process (join carbonyl carbons).

Step 2: Write Given Products
Pentan-3-one: \[ \text{CH}_3-\text{CH}_2-\text{CO}-\text{CH}_2-\text{CH}_3 \] Methanal: \[ \text{HCHO} \]

Step 3: Reverse Ozonolysis
Remove oxygen and join carbonyl carbons: \[ \text{CH}_3-\text{CH}_2-\text{C}(=\text{CH}_2)-\text{CH}_2-\text{CH}_3 \]

Step 4: Identify Longest Chain
\[ \text{CH}_2=\text{C}(\text{CH}_2\text{CH}_3)-\text{CH}_2-\text{CH}_3 \] Parent chain = But-1-ene

Step 5: Identify Substituent
Ethyl group at C-2 \[ \Rightarrow \text{2-ethylbut-1-ene} \]

Step 6: Final Answer
\[ \boxed{\text{2-ethylbut-1-ene}} \]