Practise 18 real Federal Board questions on Carbonyl compounds from 2023 to 2026. See the answer and explanation as soon as you answer.
Carbonyl compounds is one of the 19 main chapters in our Federal Board FSC Chemistry question bank (11th and 12th class), and about 4% of its real questions come from it. Tayyari Karo has 18 real questions on this chapter from 2023 to 2026; 8 are multiple choice and marked instantly, and the rest are short and long questions with a model answer. By difficulty: 9 hard, 8 medium, 1 easy.
Work through the questions below, then open the explanation for each one. Redo the ones you missed a few days later.
These are real past-paper questions. Think of your answer first, then open the explanation.
Propanone (CH₃-CO-CH₃) gives how many ¹³C NMR signals?
Answer: C. 2
Propanone has 2 distinct carbon environments: the two equivalent terminal CH₃ carbons (1 signal) and the central carbonyl carbon (1 signal), totaling 2 signals.
Which alcohol is NOT the direct product of reaction when Grignard reagent reacts with aldehydes or ketones?
Answer: D. Methanol
A Grignard reagent always adds at least one new carbon to the carbonyl compound, so a one-carbon alcohol (methanol) can never be the product.
Which will be least reactive towards nucleophilic addition reactions?
Answer: A. Acetone
Ketones like acetone are least reactive toward nucleophilic addition due to greater steric hindrance and electron donation from two alkyl groups.
Which aldehyde will show aldol condensation?
Answer: A. Ethanal
Aldol condensation requires an α-hydrogen; ethanal (CH₃CHO) has α-hydrogens, unlike formaldehyde/benzaldehyde which lack an α-carbon-H.
Which of the following carbonyl compounds is more reactive in a nucleophilic addition reaction?
Answer: B. Methanal
Methanal (formaldehyde) has the least steric hindrance and weakest electron donation to the carbonyl carbon, making it the most reactive towards nucleophilic addition.
The homologous series of ketones have general formula:
Answer: A. CₙH₂ₙO
Ketones (like aldehydes) contain one C=O per molecule with no extra unsaturation, giving the general formula CₙH₂ₙO.
Write down the mechanism of base catalysed nucleophilic addition reaction of formaldehyde (HCHO) with HCN.
Step 1: Base (OH⁻ or CN⁻ from a trace of base) removes a proton from HCN, generating the nucleophilic cyanide ion, CN⁻.
Step 2: CN⁻ attacks the electrophilic carbonyl carbon of HCHO, and the π electrons of C=O shift onto oxygen, forming an alkoxide intermediate: H₂C(O⁻)(CN).
Step 3: The alkoxide ion abstracts a proton from another HCN molecule (or water), giving the final product, glycolonitrile, HOCH₂CN, and regenerating CN⁻ to continue the cycle.
What is aldol condensation? Write its mechanism when two molecules of Acetaldehyde react together to form Crotonaldehyde.
Aldol condensation is a reaction in which two molecules of an aldehyde (or ketone) possessing α-hydrogens combine under base (or acid) catalysis, first forming a β-hydroxy aldehyde/ketone (the 'aldol'), which then loses a molecule of water (dehydration) to give an α,β-unsaturated carbonyl compound.
Mechanism (base-catalyzed) for 2 CH₃CHO → Crotonaldehyde:
Step 1: Base (OH⁻) removes an α-hydrogen from one acetaldehyde molecule, forming a resonance-stabilized enolate ion: CH₃CHO → ⁻CH₂CHO.
Step 2: This enolate carbanion (nucleophile) attacks the electrophilic carbonyl carbon of a second acetaldehyde molecule, forming an alkoxide intermediate: CH₃-CH(O⁻)-CH₂-CHO. …
The full model answer is in the app.
| Session | Questions |
|---|---|
| 2026 Annual | 1 |
| 2025 1st Annual | 6 |
| 2025 2nd Annual | 4 |
| 2024 Annual | 4 |
| 2023 Annual | 3 |
18 real Federal Board (FBISE) Chemistry questions on Carbonyl compounds from 2023 to 2026, for 11th and 12th class. Each one shows the session it came from.
No. We could not find an official FBISE marking scheme for these papers, so the answers and explanations are written by Tayyari Karo for practice. Check anything important with your teacher or textbook.
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