See image — IUPAC and Nomenclature Chemistry Question

💡 Solution & Explanation

Step 1 - Identify the substituents on the benzene ring: The structure shows a benzene ring bearing three substituents: a chlorine (Cl) at one position, a bromine (Br) adjacent to it (one carbon away), and a nitro group (NO2) on the opposite side of the ring from Cl. Step 2 - Assign the principal group and numbering: In IUPAC nomenclature for a trisubstituted benzene, we number the ring to give the lowest set of locants to the substituents. The substituents are Cl, Br, and NO2. Step 3 - Determine relative positions: From the structure, Cl and Br are on adjacent carbons (ortho, 1,2-relationship), and NO2 is two carbons away from Br (para to Cl). This gives positions 1 (Cl), 2 (Br), and 4 (NO2) when numbered to minimize locants. Step 4 - Apply alphabetical order for numbering direction: Alphabetically, Br comes before Cl and NO2. However, the numbering is chosen to give the lowest locants: assigning C1=Cl, C2=Br, C4=NO2 gives locants {1,2,4}, which is the lowest possible set. Step 5 - Construct the name: With Cl at C1, Br at C2, and NO2 at C4, the name is built as: 2-bromo (Br at 2) + 1-chloro (Cl at 1) + 4-nitro (NO2 at 4) + benzene, listed alphabetically: 2-bromo-1-chloro-4-nitrobenzene. Step 6 - Verify: The locant set {1,2,4} is indeed the lowest achievable, and alphabetical ordering of prefixes (bromo before chloro before nitro) is satisfied. Therefore, the correct answer is 2-bromo-1-chloro-4-nitrobenzene.