Priority order is very important in nomenclature.
If \(-\text{COOH}\) and \(-\text{CHO}\) are both present, choose \(-\text{COOH}\) as the principal functional group.
Step 1: Understanding the Concept:
In IUPAC nomenclature for polyfunctional aromatic compounds, the principal functional group determines the parent name.
The priority order for functional groups is: \(\text{-COOH}\) (carboxylic acid) \(>\) \(\text{-CHO}\) (aldehyde) \(>\) \(\text{-R}\) (alkyl). Step 2: Key Formula or Approach:
Identify the highest priority group as C1 and number the ring to give the remaining substituents the lowest possible locants.
The principal group here is the carboxylic acid, so the parent name is "benzoic acid". Step 3: Detailed Explanation:
1. The carboxylic acid (\(\text{-COOH}\)) is at position 1.
2. Numbering the ring to give the next substituent the lowest number: Moving toward the methyl (\(\text{-CH}_3\)) group gives it position 2.
3. Continuing the numbering, the aldehyde (\(\text{-CHO}\)) group falls at position 5.
4. When \(\text{-CHO}\) is a substituent, it is named as "formyl".
5. Alphabetically, 'f' (formyl) comes before 'm' (methyl), but we name them based on their positions in the IUPAC string.
6. The name becomes: 5-Formyl-2-methylbenzoic acid. Step 4: Final Answer:
The correct IUPAC name is 5-Formyl-2-methylbenzoic acid.
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