Primary alcohols can be oxidised to aldehydes.
Which statement shows the correct reagents and observations for this reaction?
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Reagent |
Observation |
|
A |
Acidified silver nitrate solution |
White precipitate forms |
|
B |
Fehling’s solution |
Brick-red precipitate forms |
|
C |
Tollens’ reagent |
Silver mirror forms |
|
D |
Acidified potassium dichromate |
Colour change from orange to green |
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Aldehydes can undergo oxidation reactions to form carboxylic acids.
Which equation shows the correct oxidation of an aldehyde to its corresponding carboxylic acid?
CH3CH2OH + [O] → CH3COOH + H2
CH3CHO + [O] → CH3CHCOOH
CH3CH2CHO + [O] → CH3CH2COOH
CH3COCH3 + [O] → CH3CH2COOH
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Ketones can be reduced to secondary alcohols.
Which reagents and conditions are required to reduce a ketone to a secondary alcohol?
Reflux with acidified potassium dichromate solution
Heat with aqueous sodium tetrahydridoborate
Hydrogen gas at 60 oC with a nickel catalyst
Reflux with concentrated hydrochloric acid and a tin catalyst
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Aldehydes and ketones can both react with HCN to form hydroxy nitrile compounds.
Which is the correct mechanism for this reaction?
Electrophilic addition
Electrophilic substitution
Nucleophilic addition
Nucleophilic substitution
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How many structural isomers with the molecular formula C4H8O react with Fehling’s solution?
1
2
3
4
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Lithium tetrahydridoaluminate(III), LiAlH4, in an organic solvent behaves in a similar way to sodium tetrahydridoborate, NaBH4, in an aqueous solution. If LiAlH4 reacts with a carbonyl compound, which of the following could not be formed?
3,4-dimethylhexan-2-ol
3,3-dimethylhexan-1-ol
2,3-dimethylhexan-2-ol
2,2-dimethylhexan-3-ol
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A carbonyl compound reacted with potassium cyanide followed by dilute acid. The product had no effect on plane polarised light.
Which of the following could not have been the carbonyl compound?
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Citronellal is an aldehyde that is used as an insect repellent with a characteristic lemon scent. Heptan-2-one is a ketone that gives blue cheese its distinctive aroma.
When the following tests are carried out on these compounds, which row best describes what would be noticed about these smells?
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Test |
Citronellal |
Heptan-2-one |
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A |
Acidified potassium dichromate(VI) solution and heat under reflux |
Smell disappears |
Smell disappears |
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B |
Aqueous sodium tetrahydridoborate(III) and heat under reflux |
Smell disappears |
Smell remains |
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C |
Potassium cyanide then dilute acid |
Smell remains |
Smell disappears |
|
D |
Tollens’ reagent and gently warmed |
Smell disappears |
Smell remains |
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A carbonyl compound gave a negative test result with Tollens’ reagent.
Which of the following statements is correct about the carbonyl compound?
It would produce a brick-red precipitate when reacted with Fehling’s solution
It would be reduced by aqueous sodium tetrahydridoborate(III) to a secondary alcohol
When reacted with potassium cyanide followed by dilute acid, the carbonyl would undergo a nucleophilic substitution reaction
It would undergo an oxidation reaction with acidified potassium dichromate(VI) to form a carboxylic acid and the solution would turn green
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Carbonyl compounds are reduced when reacted with potassium cyanide followed by dilute acid.
Which pair of statements about the reaction mechanism and product is not correct?
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|
Statement 1 |
Statement 2 |
|
A |
The C=O double bond is polar with the oxygen end slightly negative |
The overall charge on a cyanide ion is due to the negatively charged carbon atom |
|
B |
The cyanide ion acts as a nucleophile |
The C=O double bond breaks by homolytic fission and the oxygen atom gains an electron |
|
C |
A hydroxynitrile is formed |
This method of organic synthesis may increase the length of the carbon chain |
|
D |
The hydrogen ion that reacts with the intermediate comes from the dilute acid |
The intermediate donates a pair of electrons to a H+ ion |
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The colour of warm acidified sodium dichromate(VI) changes from orange to green when added to compound Y. 1 mol of Y reacts with 2 mol of hydrogen cyanide in the presence of potassium cyanide.
What could Y be?
H2C=CHCH2CHO
CH3CH2CH2CHO
HC(O)CH2CH2CHO
CH3COCH2COCH3
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What is formed when butanone is heated under reflux with a solution of NaBH4?
butane
butan-1-ol
butan-2-ol
butanal
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Which of the following statements about aldehydes and ketones is not true?
Shorter chain aldehydes and ketones mix completely with water
They show strong absorption in infra-red at about 1700 cm-1
Typical reactions are nucleophilic additions
They are good reducing agents
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The mechanism for the reaction between propanone and hydride ions is shown below
The correct row shown is
|
|
Role of hydride ions |
Role of propanone |
|
A |
electrophile |
nucleophile |
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B |
nucleophile |
electrophile |
|
C |
oxidising agent |
reducing agent |
|
D |
Brønsted-Lowry acid |
Brønsted-Lowry base |
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Which carbonyl compound(s) produce(s) a carboxylic acid when they are treated with acidified K2Cr2O7 or Tollens’ reagent?
CH3CH2CH2CHO and CH3CH2COCH3
CH3CH2CH2CHO and CH3CH2CH(OH)CH3
CH3COCH3
CH3CH2CH2CHO and CH3CH2CHO
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