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Question 1
Carbonyl compounds can be reduced by sodium borohydride, NaBH4. |
a) | Outline a mechanism for the reduction of butanal using NaBH4.
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b) | Name the mechanism in part a).
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c) | Explain why NaBH4 cannot be used to reduce alkenes.
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d) | A sample of butanal was reduced but insufficient NaBH4 was added. Give a chemical test, and the observation that would be made, to confirm the reaction was incomplete.
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e) | Write an overall equation for the reaction of propanone with NaBH4, Use [H] to represent the reducing agent.
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Question 2
The flowchart below shows the synthesis of a hydroxynitrile from butan-2-ol. |
a) | Give the reagent(s) and conditions required for step 1.
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b) | Give a chemical test, and the observation that would be made, to identify the carbonyl group in the product of step 1.
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c) | Give a chemical test, and the observation that would be made, to identify the CH3CO group in the product of step 1.
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d) | In step 2, butanone undergoes an addition reaction with CN- ions. Outline the mechanism for this reaction.
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e) | Name the product formed in part d).
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f) | Explain why the product in part d) has no effect on plane polarised light.
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Question 3
Pentanal reacts with KCN and dilute acid to form a racemic mixture of two stereoisomers. |
a) | Outline a mechanism for the reaction of pentanal with KCN and dilute acid.
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b) | Name the product formed in part a).
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c) | Describe how you could distinguish between separate samples of the two stereoisomers formed in the reaction in part a).
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d) | An isomer of pentanal reacts with KCN and dilute acid to produce a compound that doesn't show stereoisomerism. Draw the structure of this compound.
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e) | Explain why the compound drawn in part d) does not show stereoisomerism.
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Question 4
Butanone can be reduced using sodium borohydride, NaBH4, and dilute acid. |
a) | Write an overall equation for the reduction, using [H] to represent the reducing agent.
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b) | Explain why the product of the reduction in part a) has no effect on plane polarised light. Refer to the mechanism of the reaction in your answer.
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c) | Which of the following alcohols could not be produced by the reduction of an aldehyde or ketone? A 2-methylbutan-1-ol B 2,2-dimethylpropan-1-ol C 2-methylbutan-2-ol D pentan-3-ol
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Question 5
But-2-enal has the structural formula CH3CH=CHCHO. |
a) | Describe a chemical test, and give the observation that would be made, to confirm that but-2-enal is an aldehyde.
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b) | Draw the skeletal formula of the product that would form when but-2-enal is reacted with NaBH4.
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c) | Name the type of reaction occurring in part b).
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d) | Butanal and butanone both react with 2,4-DNPH to produce a yellow precipitate. Outline how the precipitates can be used to distinguish between the two carbonyl compounds.
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Question 6
a) | Outline a mechanism for the reaction of (CH3)2CHCHO with KCN and dilute acid.
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b) | Name the product formed in part a).
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c) | The reaction in part a) produces a pair of optical isomers. Draw the structures of these isomers.
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Question 7
The diagram below shows the structures of the compounds cinnamaldehyde and methylcinnamaldehyde. |
a) | Describe a chemical test, and give the observation that would be made, to confirm that both compounds contain an aldehyde functional group.
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b) | Describe a chemical test, and give the observation that would be made, to confirm the presence of a carbonyl group in both compounds. Include how the two compounds could be distinguished.
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c) | Complete the diagram below to show the structure of the product formed when cinnamaldehyde is reacted with NaBH4.
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d) | Complete the diagram below to show the structure of the product formed when methylcinnamaldehyde is reacted with KCN and dilute acid.
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Question 8
This question is about the aldehyde ethanal. |
a) | Describe the test for an aldehyde and give the result.
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b) | Name the reagent that is needed to convert ethanal into ethanol.
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c) | Outline the mechanism for the reaction between ethanal and KCN/H+.
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