What NEET Asks
- Direct IUPAC naming of given aldehyde or ketone structures (3-4 marks).
- Identifying the correct structure from an IUPAC name (3-4 marks).
- Questions involving isomerism where correct naming is crucial.
Key Points
- Aldehydes: Functional group -CHO. Suffix:
-al. The carbonyl carbon is always C-1. - Ketones: Functional group >C=O. Suffix:
-one. Number the chain to give the carbonyl carbon the lowest possible number. - Longest Chain: Select the longest continuous carbon chain that includes the carbonyl carbon.
- Substituents: Locate and name all substituents, indicating their positions.
- Prioritization: Aldehyde/Ketone groups take precedence over alcohols (-ol), alkenes (-ene), and alkynes (-yne) in numbering the parent chain. When -CHO is a substituent, it's called 'formyl' or 'oxo'. When >C=O is a substituent, it's 'oxo'.
- Cyclic Compounds: For -CHO directly attached to a ring, use 'carbaldehyde' as a suffix (e.g., Cyclohexanecarbaldehyde).
Must-Know Formula / Reaction
- Aldehyde: R-CHO (R = alkyl/aryl group, CHO = formyl group). Suffix: -al. Example: CH₃CHO (Ethanal).
- Ketone: R-CO-R' (R, R' = alkyl/aryl groups, CO = carbonyl group). Suffix: -one. Example: CH₃COCH₃ (Propan-2-one).
Common Mistakes
- Students often fail to assign C-1 correctly for aldehydes, sometimes numbering from the wrong end.
- Don't confuse the suffixes
-al(aldehyde) and-ol(alcohol) or-one(ketone) and-ene(alkene). - Incorrectly numbering the parent chain in ketones, not giving the carbonyl carbon the lowest possible position.
Rapid Revision
Remember that aldehydes are always terminal (C-1) and use -al. Ketones are internal, requiring a locant for the carbonyl carbon, and use -one. Prioritize the carbonyl group in numbering the parent chain. For cyclic aldehydes, use the 'carbaldehyde' suffix.