Carbonyl compounds — AS & A Level Chemistry (9701) questions by topic
Nucleophilic addition and 2,4-DNPH testing define this topic: tracing propanone's reactions with KCN and HCN, identifying which compound gives a yellow-orange precipitate with 2,4-dinitrophenylhydrazine, and pairing reagents that create a chiral carbon in the product.
Deduce, identify, state, explain and draw lead 45 questions from 2023 to 2025 papers, worth 1 to 11 marks, where miscounting isomeric structures is the most frequent way to lose a mark. Checking each reagent choice and isomer count with instant marking flags an incomplete count of eight isomeric carbonyl structures before the same undercounting habit affects a later isomer question.
What examiners look for
- A common mistake was choosing B, since acidified sodium dichromate(VI) would also oxidise an alcohol group to a ketone where selectivity was needed.
- Examiners flag choosing B or C as the most common wrong answers from not counting all eight isomeric structures.
- A recurring criticism is failing to count the two optical isomers of 2-methylbutanal separately.
- Strong answers recognised that reducing a carbonyl group needs NaBH4, while selectively oxidising an aldehyde in the presence of a ketone needs Tollens' reagent followed by acidification rather than dichromate.
- Candidates who identified all eight isomeric carbonyl structures, including both optical isomers of 2-methylbutanal, scored full marks.
May–June 2025, Paper 11
Information about carbonyl compound X is given. - Compound X reacts with LiAlH4 to produce a secondary alcohol. - Compound X reacts with alkaline I2(aq) to give a yellow…
Answer this question and get it marked →May–June 2025, Paper 12
Methanoic acid, HCO2H, has acidic properties similar to those of other carboxylic acids. In addition, it can be oxidised by the same oxidising agents that are capable of oxidising…
Answer this question and get it marked →Butan-2-one reacts with alkaline I2(aq). An excess of dilute sulfuric acid is then added to the reaction mixture. The organic products of this reaction sequence are triiodomethane…
Answer this question and get it marked →May–June 2025, Paper 13
What is formed when propanone is heated under reflux with a solution of NaBH4? A propan-2-ol B propan-1-ol C propanal D propane
Answer this question and get it marked →Compound P displays cis/trans isomerism and gives a red-brown precipitate with Fehling's solution. What is P? A H2C=C(CH2CHO)/CH3 — has both C=C for cis/trans and aldehyde? No B H…
Answer this question and get it marked →May–June 2025, Paper 14
Acidified potassium dichromate(VI), K2Cr2O7, is added to propan-1-ol and the mixture is immediately distilled. The distillate is treated with HCN in the presence of KCN. What is…
Answer this question and get it marked →Compound Q gives positive results when tested separately with alkaline I2(aq) and with Tollens' reagent. What is compound Q? A CHOCH2CH2CHO B CH3CH2COCHO C CH3COCH2CHO D CH3COCOCH3
Answer this question and get it marked →May–June 2025, Paper 21
State the functional group in ethanal, propanal and propanone.
Answer this question and get it marked →May–June 2024, Paper 11
X is a non-cyclic ketone with a single carbonyl group and no other functional groups. Ketone X has the following properties. - When ketone X is treated with NaBH4, the organic…
Answer this question and get it marked →Compound Y: - changes the colour of acidified K2Cr2O7 from orange to green - has no effect on Fehling's reagent - produces an orange precipitate with 2,4-dinitrophenylhydrazine…
Answer this question and get it marked →The product of the reaction between propanone and hydrogen cyanide is hydrolysed under acidic conditions. What is the formula of the final product? A CH3CH(OH)COOH B CH3CH2CH2COOH…
Answer this question and get it marked →May–June 2024, Paper 12
In which reaction is the organic compound oxidised? A CH3CH2CH2CHO + Tollens' reagent B CH3CH2CH2CHO + LiAlH4 C CH3CH2CH2OH + concentrated H3PO4 D CH3CO2C2H5 + dilute H2SO4
Answer this question and get it marked →The diagram shows a simplified structure of coenzyme Q10: a quinone ring (a 6-membered ring with two C=O groups) bearing two CH3O- substituents and a methyl group, attached to a…
Answer this question and get it marked →Which pair of reagents reacts to form a product with a chiral carbon atom? A CH3CH=CH2 + HBr B (CH3)2C=O + NaBH4 C CH3CH2CHO + HCN D CH3COOH + CH3CH2OH
Answer this question and get it marked →May–June 2024, Paper 13
Four different alcohols are treated with alkaline I2(aq). Which row is correct? name of alcohol formulae of products --- --- --- A butan-2-ol CH3COO^- and CH3CI3 B propan-1-ol…
Answer this question and get it marked →Butanedione, CH3COCOCH3, is a yellow liquid. How does butanedione react with 2,4-dinitrophenylhydrazine reagent and Fehling's reagent? 2,4-dinitrophenylhydrazine Fehling's --- ---…
Answer this question and get it marked →Compound Q reacts separately with HCN and NaBH4 under suitable conditions. Both reactions produce an organic product with a chiral centre. What is compound Q? A butanone B ethanal…
Answer this question and get it marked →Compound X has the following properties. - When 0.20 mol of X undergoes complete combustion, 14.4 dm^3 of carbon dioxide is produced, measured under room conditions. - X reacts…
Answer this question and get it marked →October–November 2024, Paper 11
Compound Y reacts with alkaline I₂(aq). When the products of this reaction are acidified, a dicarboxylic acid is produced. The formula of the dicarboxylic acid is HOOC–R–COOH…
Answer this question and get it marked →Which compound, on reaction with hydrogen cyanide, produces a compound with a chiral centre? A CH₃CHO B CH₃CH₂COCH₂CH₃ C CH₃CO₂CH₃ D HCHO
Answer this question and get it marked →The diagram shows three reactions of ethanal, CH₃CHO. In each case an excess of ethanal is used. Ethanal reacts with acidified K₂Cr₂O₇ with heat to give solution 1; with alkaline…
Answer this question and get it marked →October–November 2024, Paper 12
Compound X: - does not react with Tollens' reagent - forms a yellow precipitate with alkaline I₂(aq) - does not react with sodium. What could be the identity of X? A CH₃CHO B…
Answer this question and get it marked →Which compound can undergo nucleophilic addition? A bromoethane, C₂H₅Br B ethanal, CH₃CHO C ethane, C₂H₆ D ethene, C₂H₄
Answer this question and get it marked →October–November 2024, Paper 13
Compound Y reacts with alkaline I₂(aq). When the products of this reaction are acidified, a dicarboxylic acid is produced. The formula of the dicarboxylic acid is HOOC–R–COOH…
Answer this question and get it marked →Which compound, on reaction with hydrogen cyanide, produces a compound with a chiral centre? A CH₃CHO B CH₃CH₂COCH₂CH₃ C CH₃CO₂CH₃ D HCHO
Answer this question and get it marked →The diagram shows three reactions of ethanal, CH₃CHO. In each case an excess of ethanal is used. Ethanal reacts with acidified K₂Cr₂O₇ with heat to give solution 1; with alkaline…
Answer this question and get it marked →October–November 2024, Paper 21
Propanone, CH₃COCH₃, is an important organic reagent. Fig. 4.1 shows some reactions of propanone and its derivatives. Propanone reacts with KCN and HCN (reaction 1) to give A, a…
Answer this question and get it marked →October–November 2024, Paper 23
Propanone, CH₃COCH₃, is an important organic reagent. Reaction 1 is a nucleophilic addition reaction. Complete Fig. 4.2 to show the mechanism for the formation of A from…
Answer this question and get it marked →February–March 2023, Paper 12
Structural and stereoisomerism should be considered when answering this question. P has molecular formula C5H10O. P produces an orange precipitate with 2,4-dinitrophenylhydrazine…
Answer this question and get it marked →Two isomeric alcohols, W and X, have molecular formula C4H9OH. W is oxidised to carbonyl compound Y which gives a red precipitate with Fehling's solution. X is oxidised to…
Answer this question and get it marked →May–June 2023, Paper 11
Which reagent can confirm the presence of a carbonyl group in an organic compound and does not distinguish between aldehydes and ketones? A acidified K2Cr2O7 B 2,4-DNPH reagent C…
Answer this question and get it marked →Which compound gives a positive test with alkaline aqueous iodine and does not show optical isomerism? A CH3COCH2CH2OH B CH3CH2CH(OH)CHO C CH3COCH(OH)CH3 D (CH3)2C(OH)CHO
Answer this question and get it marked →Two samples of compound X were treated separately with different reagents which were added in excess. Compound X is a hydroxy-ketone-aldehyde (a chain bearing a secondary alcohol,…
Answer this question and get it marked →May–June 2023, Paper 12
Compound G gives a pale yellow precipitate with alkaline I2(aq). What could be compound G? A pentan-1-ol B pentan-2-ol C pentan-3-ol D 2-methylpentan-2-ol
Answer this question and get it marked →The mechanism for the reaction between ethanal and hydrogen cyanide starts with the step shown: a cyanide ion (CN-) attacks the carbonyl carbon of ethanal (CH3CHO) and the pi…
Answer this question and get it marked →Which compound reacts with 2,4-dinitrophenylhydrazine reagent but does not react with Tollens' reagent? A CH3COCO2H B CH3CH(OH)CHO C CH3COCHO D CH3CH(OH)CH3
Answer this question and get it marked →Compound X has stereoisomers and forms a precipitate when warmed with Fehling's reagent. What could be the structure of compound X? Four skeletal structures are shown. A:…
Answer this question and get it marked →May–June 2023, Paper 13
T is an organic compound which contains 66.7% by mass of carbon. T also contains one atom of oxygen per molecule. T reacts with alkaline I2(aq) to produce a yellow precipitate.…
Answer this question and get it marked →Which statement about butanone is correct? A Butanone can be dehydrated by concentrated sulfuric acid to give CH2=CHCH=CH2. B Butanone gives a positive result with Tollens'…
Answer this question and get it marked →October–November 2023, Paper 11
Which compound will produce a yellow-orange precipitate when added to 2,4-dinitrophenylhydrazine? A: cyclohexene. B: a cyclic ester (lactone). C: cyclohexanecarboxylic acid. D:…
Answer this question and get it marked →Ethanal, CH3CHO, undergoes an addition reaction with HCN in the presence of CN- ions. Which row identifies the type of reaction and the name of the product formed? A:…
Answer this question and get it marked →October–November 2023, Paper 12
The formulae of three compounds are shown: C3H7CHO, C2H5COCH3 and CH2CHCH2CH2OH. Only one of these compounds will decolourise bromine water; only one will produce a silver mirror…
Answer this question and get it marked →Which reaction takes place by a nucleophilic addition mechanism? A: propene reacting with hydrogen bromide. B: 2-bromopropane reacting with sodium hydroxide in ethanol. C:…
Answer this question and get it marked →October–November 2023, Paper 13
Which compound will produce a yellow-orange precipitate when added to 2,4-dinitrophenylhydrazine? A cyclohexene (a cyclohexane ring with one C=C double bond). B a six-membered…
Answer this question and get it marked →Ethanal, CH3CHO, undergoes an addition reaction with HCN in the presence of CN- ions. Which row identifies the type of reaction and the name of the product formed? type of…
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