Question

One mole of an alkene on ozonolysis gives a mixture of one mole pentan-3-one and one mole methanal. The alkene is (2024)

• 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:

To solve ozonolysis problems quickly, just look at the names of the products. "Methanal" always indicates a terminal double bond ($=CH_2$). "Pentan-3-one" shows the branching occurs at the third carbon of a 5-carbon sequence.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Ozonolysis is a reaction where the double bond ($C=C$) of an alkene is cleaved and replaced by two carbonyl ($C=O$) groups. To find the original alkene, we can "reverse" the process by removing the oxygen atoms from the products and joining the carbon atoms with a double bond.
Step 2: Key Formula or Approach:
1. Draw the structures of the products.
2. Align the carbonyl groups ($C=O$) facing each other.
3. Remove the Oxygens and join the Carbons: $R_2C=O + O=CR'_2 \rightarrow R_2C=CR'_2$.
Step 3: Detailed Explanation:
1. Product 1: Pentan-3-one ($CH_3-CH_2-CO-CH_2-CH_3$).
2. Product 2: Methanal ($H-CO-H$ or $CH_2O$).
3. Aligning the $C=O$ groups: \[ (CH_3-CH_2)_2C=O \quad + \quad O=CH_2 \] 4. Joining the carbons results in: \[ (CH_3-CH_2)_2C=CH_2 \] 5. The IUPAC name for this structure is 2-ethylbut-1-ene.
(Chain: $C_1=C_2(CH_2CH_3)-C_3H_2-C_4H_3$ with an ethyl group at position 2).
Step 4: Final Answer:
The alkene is 2-ethylbut-1-ene.