See image — IUPAC and Nomenclature Chemistry Question

💡 Solution & Explanation

Step 1: Identify the structure. The compound is CH3-CH(CH3)-C(=O)-COOH. Written out: a carboxylic acid group (COOH) attached to a carbonyl carbon (C=O, i.e., a keto group), which is attached to a CH bearing a methyl group, which is attached to a terminal CH3. Step 2: Determine the parent chain. The longest chain that includes the principal characteristic group (COOH) and the maximum number of carbons: C1(OOH)-C2(=O)-C3(H)(CH3)-C4(H3). This gives a 4-carbon chain: butanoic acid. Step 3: Number the chain. The COOH carbon is C1, the keto carbon is C2, the CH(CH3) is C3, and the terminal CH3 is C4. Step 4: Identify substituents and their positions. - At C2: oxo group (=O), giving '2-oxo' - At C3: methyl group, giving '3-methyl' Step 5: Construct the IUPAC name. Parent chain: butanoic acid. Substituents: 3-methyl, 2-oxo. Full name: 3-Methyl-2-oxobutanoic acid. Step 6: Evaluate other options. (a) '3-Methyl-2-oxobutanecarboxylic acid' implies COOH is a substituent on a butane chain (5 carbons total), which is incorrect because COOH is the principal group and part of the main chain. (b) '2-Methyl-3-oxobutan-4-oic acid' has incorrect numbering and locant for the acid. (d) '3-Methyl-1,2-dioxobutanoic acid' would imply two oxo groups at C1 and C2, but C1 of a butanoic acid is the COOH carbon itself, not a ketone; only one keto group exists at C2. Therefore, the correct answer is C.