Question

One mole of an alkene on ozonolysis gives two moles of propanone. What is the alkene?

• A. 1,3-Butadiene
• B. 2,3-Dimethyl-2-butene
• C. 2,3-Dimethyl-1-butene
• D. 2-Methyl-1-butene
• E. 2-Methyl-1,3-butadiene

Hint:

To solve ozonolysis problems backward:
1. Identify the products.
2. Remove the \(=O\) from each product.
3. Join the remaining carbon fragments with a double bond.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Ozonolysis is a reaction where an alkene's double bond (\(C=C\)) is cleaved and replaced by carbonyl groups (\(C=O\)) at each carbon atom of the former double bond.

Step 3: Detailed Explanation:
The product given is propanone (acetone), which has the structure:
\[ CH_3-CO-CH_3 \]
Since two moles of propanone are formed, we "reverse" the ozonolysis by removing the oxygen atoms and connecting the two carbonyl carbons with a double bond.
\[ (CH_3)_2C=O + O=C(CH_3)_2 \xrightarrow{\text{Reverse Ozonolysis}} (CH_3)_2C=C(CH_3)_2 \]
The IUPAC name for this structure is 2,3-Dimethyl-2-butene.
Structure:
\[ CH_3 - \overset{CH_3}{\underset{|}{C}} = \overset{CH_3}{\underset{|}{C}} - CH_3 \]

Step 4: Final Answer:
The alkene is 2,3-dimethyl-2-butene.