When naming substituted benzoic acids, the -COOH group is always at position 1. Number the benzene ring to give the lowest possible numbers to the other substituents based on their priority (functional groups>halogens>nitro groups). Finally, list the substituents alphabetically with their corresponding position numbers before the parent name "benzoic acid".
The given compound is a substituted benzoic acid. To determine its IUPAC name, let's analyze the structure:
The main functional group is the carboxylic acid (\(\text{CO}_{2}\text{H}\)), and it is located on the benzene ring. This makes the compound a benzoic acid derivative.
The numbering of the benzene ring starts from the carbon attached to the carboxylic acid group (\(\text{CO}_{2}\text{H}\)). This is position 1.
Identify and number the substituents on the benzene ring:
\(\text{OH}\) (hydroxy group) is on position 2.
\(\text{Br}\) (bromo group) is on position 3.
\(\text{NO}_{2}\) (nitro group) is on position 5.
Following IUPAC nomenclature, the substituents are listed in alphabetical order: Bromo, Hydroxy, Nitro.
Thus, the correct IUPAC name is 3-Bromo-2-hydroxy-5-nitrobenzoic acid.
Justification:
Options Explanation:
3-Bromo-2-hydroxy-5-nitrobenzoic acid: This matches our analysis.
3-Bromo-4-hydroxy-1-nitrobenzoic acid: Incorrect because the hydroxy group is at position 2, not 4.
2-Hydroxy-3-bromo-5-nitrobenzoic acid: Incorrect sequence according to alphabetical order for naming.
5-Nitro-3-bromo-2-hydroxybenzoic acid: Incorrect sequence according to alphabetical order for naming.
Therefore, the correct answer is 3-Bromo-2-hydroxy-5-nitrobenzoic acid.
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Approach Solution -2
To determine the correct IUPAC name, we need to follow the IUPAC nomenclature rules for substituted benzoic acids.
1. Identify the parent compound: The parent compound is benzoic acid, as it contains a benzene ring with a -COOH group. The -COOH group is assigned position 1.
2. Number the benzene ring: The numbering of the ring is done such that the substituent with the next priority gets the lowest possible number. The priority order for the substituents present is: -COOH (highest priority, assigned position 1)>-OH>-Br>-NO\( _2 \). Therefore, the -OH group should get the lowest possible number. Numbering clockwise gives -OH at position 2, -Br at position 3, and -NO\( _2 \) at position 5. Numbering counterclockwise would give -OH at position 6, which is higher. Thus, the clockwise numbering is correct.
3. Identify the substituents and their positions: - -Br (bromo) is at position 3. - -OH (hydroxy) is at position 2. - -NO\( _2 \) (nitro) is at position 5.
4. Arrange the substituents alphabetically: The alphabetical order of the prefixes is bromo, hydroxy, nitro.
5. Write the IUPAC name: Combining the position numbers and the alphabetically ordered prefixes with the parent name benzoic acid, we get: 3-bromo-2-hydroxy-5-nitrobenzoic acid. This matches option (1).
