Question

The IUPAC name of mesityl oxide is

• A. 2-Methylpent-2-en-3-one
• B. 3-Methylpent-2-en-4-one
• C. 4-Methylpent-2-en-3-one
• D. 4-Methylpent-3-en-2-one
• E. 2-Methylpent-3-en-4-one

Hint:

Mesityl oxide is a common "trick name" in exams. Always remember it as the "acetone dimer product" to reconstruct its structure if you forget the IUPAC name.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Mesityl oxide is a common name for an \(\alpha, \beta\)-unsaturated ketone formed by the aldol condensation of acetone followed by dehydration.
Step 2: Key Formula or Approach:
Acetone + Acetone \(\rightarrow\) 4-hydroxy-4-methylpentan-2-one \(\xrightarrow{-H_2O}\) Mesityl Oxide.
Structure: \( (CH_3)_2C=CH-COCH_3 \).
Step 3: Detailed Explanation:
1. Identify the longest chain containing the ketone and double bond: 5 carbons (Pent-).
2. Number the chain giving the ketone the lowest number: Carbon 2 is C=O.
3. The double bond starts at Carbon 3 (-3-en).
4. A methyl group is at Carbon 4 (4-Methyl).
Name: 4-Methylpent-3-en-2-one.
Step 4: Final Answer:
The IUPAC name is 4-Methylpent-3-en-2-one.