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: Recall the structure of mesityl oxide.
Mesityl oxide is a well-known compound obtained from the condensation of acetone. Its structure is \(\mathrm{CH_3COCH=C(CH_3)_2}\). This compound contains both a ketone group and a carbon-carbon double bond, so its IUPAC name must reflect both functionalities correctly.
Step 2: Choose the longest carbon chain.
The longest chain containing the ketone group and the double bond has five carbon atoms. Therefore, the parent hydrocarbon is pentene with a ketone functional group, so the base name will be derived from pentenone.
Step 3: Number the chain correctly.
In IUPAC nomenclature, the ketone group gets priority in numbering. So numbering is done from the end nearer to the carbonyl carbon. This gives:

• ketone group at carbon 2,
• double bond between carbon 3 and carbon 4,
• one methyl substituent at carbon 4.

Thus, the correct IUPAC name becomes \(\mathrm{4\text{-}methylpent\text{-}3\text{-}en\text{-}2\text{-}one}\).
Step 4: Conclusion.
Hence, the IUPAC name of mesityl oxide is 4-methylpent-3-en-2-one.
Final Answer:4-methylpent-3-en-2-one.