Question

• A. 5-methylcyclohex-3-en-1-one
• B. 3-methylcyclohex-5-en-1-one
• C. 5-methylcyclohex-1-en-3-one
• D. 3-methylcyclohex-1-en-5-one

Answer 1

Answer: (A)

5-methylcyclohex-3-en-1-one

Answer 2

The carbonyl carbon is assigned position 1. The ring is numbered to give the double bond the lowest possible locant. Numbering the ketone as C1, the double bond is between C3 and C4, and the methyl group is at C5. This leads to the IUPAC name 5-methylcyclohex-3-en-1-one.