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CAIE A-Level Chemistry AS 17.1 Aldehydes and Ketones Questions

Practise aldehyde and ketone questions using preparation routes, nucleophilic addition mechanisms and tests for carbonyl identity.

Syllabus
2028–2030
Course
Chemistry 9701
Level
AS

Exam points

  • interpret oxidation and reduction sequences to identify aldehyde, ketone or alcohol products
  • draw or describe HCN addition mechanisms using CN- attack and protonation
  • use 2,4-DNPH, Tollens' reagent and alkaline I2 to identify unknown carbonyls

Covered syllabus points

17.1.1—Preparation of aldehydes and ketones17.1.2—Describe17.1.3—Reactions of hydrogen cyanide17.1.4—2,4-DNPH carbonyl test17.1.5—The nature (aldehyde or ketone) of an unknown17.1.6—Iodoform test for CH3CO- group

Question 1

[Maximum number: 8]

4(CH3)3CCHO4\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCHO} is used in the synthesis of some antibiotics.

Question (a)

(a)

Two reaction sequences are shown.

Figure for Question (a) — CAIE A-Level Chemistry AS
Figure for Question (a) — CAIE A-Level Chemistry AS
[ 2 ]

Question (i)

(i)

Reaction 1 is an oxidation reaction.

Identify the reagent(s) and conditions for reaction 1.

[ 1 ]

Question (ii)

(ii)

Give the balanced equation for the reaction of (CH3)3CCHO\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCHO} with NaBH4\mathrm{NaBH}_{4} to form S.

Use [H] to represent an atom of hydrogen provided by NaBH4\mathrm{NaBH}_{4}.

[ 1 ]

Question (b)

(b)

X, Y and Z are all isomers of (CH3)3CCHO\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCHO}.

A summary of some of the reactions and properties of X, Y and Z is shown in the table.

Table for Question (b) — CAIE A-Level Chemistry AS
[ 6 ]

Question (i)

(i)

X and Y each contains a carbonyl group.

Complete the table with the expected observations for the reactions of X and Y with 2,4-DNPH.

[ 1 ]

Question (ii)

(ii)

Identify the functional group present in Y that causes the recorded observation with Fehling's solution.

[ 1 ]

Question (iii)

(iii)

X contains a carbonyl group. X reacts with HCN , in the presence of a small amount of NaCN , to form (C2H5)2C(OH)CN\left(\mathrm{C}_{2} \mathrm{H}_{5}\right)_{2} \mathrm{C}(\mathrm{OH}) \mathrm{CN} as shown.

X+HCN→(C2H5)2C(OH)CN\mathbf{X}+\mathrm{HCN} \rightarrow\left(\mathrm{C}_{2} \mathrm{H}_{5}\right)_{2} \mathrm{C}(\mathrm{OH}) \mathrm{CN}

Draw the mechanism of the reaction of X with HCN .
- Draw the structure of X and the intermediate.
- Include all charges, partial charges, lone pairs and curly arrows.

Figure for Question (iii) — CAIE A-Level Chemistry AS
[ 3 ]

Question (iv)

(iv)

State the role of NaCN in the reaction in (c)(vii).

[ 1 ]
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