Question

What is the IUPAC name of Mesityl oxide?

• A. 3-methylpent-4-en-2-one
• B. 4,4-dimethylbut-3-en-2-one
• C. 4-methylpent-3-en-2-one
• D. 1-methylpent-2-en-4-one

Hint:

In compounds having both double bond and ketone group, numbering is done in such a way that the ketone group gets the lowest possible number because it has higher priority.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Mesityl oxide is a common name for the $\alpha, \beta$-unsaturated ketone formed by the aldol condensation of acetone.
Step 2: Formula Application:
Structure: $(CH_3)_2C=CH-COCH_3$.
Step 3: Explanation:
1. Number the chain from the carbonyl end: $C_1(H_3)-C_2(=O)-C_3(H)=C_4(CH_3)-C_5(H_3)$. 2. The double bond starts at $C_3$. 3. The ketone is at $C_2$. 4. A methyl branch is at $C_4$. Name: 4-methylpent-3-en-2-one.
Step 4: Final Answer:
The IUPAC name is 4-methylpent-3-en-2-one.