See image — IUPAC and Nomenclature Chemistry Question

💡 Solution & Explanation

Step 1 - Identify the parent ring and functional groups: The structure shows a six-membered carbocyclic ring (cyclohexane backbone) with one double bond, a methyl substituent on one carbon of the double bond, and a terminal alkyne (ethynyl, –C≡CH) group on the carbon para to the methyl-bearing carbon. Step 2 - Identify the parent chain/ring name: Because there is a double bond in the ring, the parent is cyclohexene. Step 3 - Number the ring to give lowest locants: The double bond carbons receive the lowest possible numbers. Place C1 and C2 at the double bond. The methyl group is attached directly to C1 (one of the sp2 carbons), so C1 carries the methyl group. Numbering proceeds so that the ethynyl substituent receives the lowest possible locant consistent with the double bond numbering, placing it at C4. Step 4 - Name the substituents: The –CH3 group is a methyl substituent; the –C≡CH group is an ethynyl substituent. Step 5 - Assemble the IUPAC name: List substituents alphabetically with their locants before the parent name: 4-ethynyl-1-methylcyclohexene. The '1-' for the double bond start is implied at C1, and the ring double bond is between C1 and C2. Step 6 - Verify: No other numbering gives lower locants for the set {double bond, methyl, ethynyl}, confirming 4-ethynyl-1-methylcyclohexene is correct. Therefore, the correct answer is 4-ethynyl-1-methylcyclohexene.