See image — IUPAC and Nomenclature Chemistry Question

💡 Solution & Explanation

Step 1 - Identify the compound: CH3—CH=CH—COOH is a four-carbon chain containing a carboxylic acid group and a carbon-carbon double bond. Step 2 - Count the carbons: The chain has 4 carbons total (C1 = COOH carbon, C2 = CH=, C3 = =CH, C4 = CH3), so the parent chain is 'but'. Step 3 - Identify functional groups: There is a carboxylic acid (-COOH) and an alkene (C=C double bond). In IUPAC nomenclature, the carboxylic acid carbon is C1 (highest priority, gets lowest locant). Step 4 - Locate the double bond: With C1 as the COOH carbon, the double bond is between C2 and C3, so it is designated 'ene-2' or 'but-2-ene'. Step 5 - Name the acid: The suffix for the carboxylic acid when the COOH carbon is part of the chain is '-oic acid'. The full name is But-2-ene-1-oic acid (the '1' indicates the COOH is at C1). Step 6 - Eliminate incorrect options: (b) But-1-ene-1-oic acid would place the double bond between C1 and C2, but C1 is the COOH carbon which already has a double bond to oxygen, so a C=C at position 1 is structurally inconsistent with this compound. (c) But-2-ene-1-carboxylic acid is incorrect because '-carboxylic acid' suffix is used when the COOH is attached to a ring or the COOH carbon is NOT counted in the parent chain; here the COOH carbon IS part of the chain. (d) Propene-1-carboxylic acid incorrectly counts only 3 carbons in the parent chain and uses the wrong suffix style. Therefore, the correct answer is A.