In aromatic compounds with more than one substituent, the substituents are numbered to give the lowest possible locants, with the substituent listed first in alphabetical order.
To solve the problem, we need to determine the correct IUPAC name for the given compound, which is a benzene ring with a methyl group (CH\(_3\)) and a chlorine (Cl) substituent.
1. Identifying the Structure: The compound is a benzene ring with two substituents: a methyl group (CH\(_3\)) and a chlorine atom (Cl). From the diagram, the methyl group and chlorine are positioned on the benzene ring, and we need to determine their relative positions.
2. Determining the Positions: In the benzene ring, the positions of substituents are numbered 1 through 6. Let’s assume the methyl group is at position 1 (as is common in IUPAC naming to give the lowest possible numbers). The diagram shows the methyl group and chlorine in a para relationship (opposite each other, 1,4-positions). Thus, if the methyl group is at position 1, the chlorine is at position 4.
3. Naming the Compound: In IUPAC nomenclature for a disubstituted benzene, the substituents are named in alphabetical order, and the lowest possible numbers are assigned to their positions. Here, the substituents are: - Chloro (Cl) - Methyl (CH\(_3\)) Alphabetically, "chloro" (C) comes before "methyl" (M), so "chloro" is assigned the lowest possible number. If methyl is at position 1, chlorine is at position 4, making the name 1-methyl-4-chlorobenzene. Alternatively, if chlorine is at position 1, methyl is at position 4, giving 1-chloro-4-methylbenzene. Since "chloro" precedes "methyl" alphabetically, 1-chloro-4-methylbenzene is preferred.
4. Evaluating the Options: - Option A: Methylchlorobenzene This name does not follow IUPAC rules, as it lacks positional numbers and is not a systematic name. Incorrect. - Option B: Toluene Toluene is methylbenzene (C\(_6\)H\(_5\)CH\(_3\)), with only a methyl group and no chlorine. Incorrect. - Option C: 1-Chloro-4-Methylbenzene This matches our deduced name: chlorine at position 1, methyl at position 4, following alphabetical priority. Correct. - Option D: 1-Methyl-4-Chlorobenzene This is the same compound as option C but prioritizes "methyl" over "chloro," which violates the alphabetical rule in IUPAC naming. Incorrect.
Final Answer: The correct IUPAC name for the compound is 1-chloro-4-methylbenzene (option C).
