Nucleophilic addition with cyanideAQA A-Level Chemistry: Subtopic test

1. 1
   A student adds potassium cyanide solution to ethanal, then adds dilute sulfuric acid. A hydroxynitrile is formed in a nucleophilic addition reaction.

   (a)

   What is the organic product of the reaction of ethanal with KCN followed by dilute acid?

   [1 mark]

   • APropanenitrile
   • B2-Hydroxypropanoic acid
   • C2-Hydroxypropanenitrile
   • DPropan-2-ol

   (b)

   Which species acts as the nucleophile in this reaction?

   [1 mark]

   • ACN⁻
   • BHCN
   • CH⁺
   • DK⁺

   (c)

   State the role of the dilute acid in the reaction and give one hazard of using KCN.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A chemist is investigating the reactions of several carbonyl compounds with KCN followed by dilute acid. The products are hydroxynitriles, and the chemist wants to know which of the products contain a chiral centre.

   (a)

   The product of propanone with KCN followed by dilute acid is 2-hydroxy-2-methylpropanenitrile, (CH₃)₂C(OH)CN. Which statement about this product is correct?

   [1 mark]

   • AIt forms a racemic mixture
   • BIt contains a chiral centre
   • CIt rotates plane-polarised light
   • DIt does not contain a chiral centre

   (b)

   Which carbonyl compound would give a product that is a mixture of enantiomers with KCN followed by dilute acid?

   [1 mark]

   • APropanone
   • BButanal
   • CPentan-3-one
   • DMethanal

   (c)

   Butanone, CH₃COCH₂CH₃, reacts with HCN. Write the overall equation for this reaction and name the organic product.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Propanal is added to a solution of KCN in a fume cupboard. Dilute acid is then added to the mixture. The organic product is a hydroxynitrile.

   (a)

   Write the overall equation for the reaction of propanal with HCN, name the organic product, and name the type of mechanism.

   [3 marks]

   (b)

   Outline the mechanism for the reaction of propanal with KCN followed by dilute acid, including the movement of electron pairs.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A school technician prepares 2-hydroxybutanenitrile from propanal using potassium cyanide and dilute sulfuric acid. The product is then placed in a polarimeter and is found not to rotate plane-polarised light.

   (a)

   Explain why the product of this reaction does not rotate plane-polarised light, even though its molecules are chiral.

   [6 marks]

   (b)

   Describe the hazards of using potassium cyanide in this preparation and explain how the risks can be reduced.

   [6 marks]

   Total for question 4: 12 marks

End of questions