What NEET Asks
- Direct IUPAC naming of simple and substituted carboxylic acids is a fundamental skill tested.
- Questions often involve the priority of -COOH over other functional groups in complex molecules.
- Expect 1-2 questions from nomenclature in the organic chemistry section, typically carrying 4-8 marks.
Key Points
- The -COOH group (carboxyl group) is the highest priority functional group in IUPAC nomenclature.
- Numbering of the parent chain always starts from the carbon of the -COOH group, assigning it C1, when it's part of the continuous chain.
- The suffix "-oic acid" is used for open-chain carboxylic acids where the -COOH carbon is included in the parent chain.
- If the -COOH group is attached to a ring system or if there are more than two identical -COOH groups in the compound, the suffix "-carboxylic acid" is used.
- For dicarboxylic acids (two -COOH groups), the suffix is "-dioic acid", e.g., HOOC-CH2-COOH is Propanedioic acid.
- The longest carbon chain containing the -COOH group(s) is always selected as the parent chain.
Must-Know Formula / Reaction
- General IUPAC Naming Rule: (Locant of Substituent) - (Substituent Name) - (Parent Alkane Name) - (Suffix: -oic acid / -dioic acid / -carboxylic acid)
- Example 1: CH3CH2COOH → Propanoic acid (Parent: Propane, Suffix: -oic acid)
- Example 2: HOOC-CH2-CH2-COOH → Butane-1,4-dioic acid (Parent: Butane, Suffix: -dioic acid)
Common Mistakes
- Students often forget to include the carbon of the -COOH group in the parent chain when using the "-oic acid" suffix.
- Don't confuse the usage of "-oic acid" (COOH carbon part of chain) with "-carboxylic acid" (COOH carbon not part of main chain, or attached to a ring).
- Incorrectly identifying the longest carbon chain or assigning priority when multiple functional groups are present in a molecule.
Rapid Revision
Identify the -COOH group and ensure its carbon is C1 for open chains. Find the longest chain. Use "-oic acid" for simple chains, "-dioic acid" for two COOH, and "-carboxylic acid" for rings or when more than two COOH groups are present and cannot all be included in the main chain. Prioritize numbering to give substituents the lowest possible locants.