Aldehydes and ketones

This question is about oxidation.

A student has separate unlabelled samples of propan-1-ol and propan-2-ol but does not know which sample is which alcohol.

The student plans a series of steps to identify the alcohols.

Step 1 Oxidise each sample, distilling off the organic product as it is formed. Step 2 Identify the organic products using a simple chemical test. Step 3 Confirm the identities using the infrared spectrum of each original sample.

Give further details of each step in the plan. In your answer include

• an appropriate oxidising agent used in Step 1

• equations, using [O] to represent the oxidising agent, for each reaction in Step 1

• a suitable test and expected observations in Step 2

• how the infrared spectra can be used to confirm the identities.

A primary alcohol can be oxidised to form a carboxylic acid using an excess of the oxidising agent in Question 05.1.

Give the condition needed for this reaction.

Complete the diagram, adding labels, to show how the apparatus would be set up.

During oxidation reactions, anti-bumping granules are often added to the pear-shaped flask containing the reactants.

State why anti-bumping granules are used.

This question is about simple test-tube reactions to identify organic liquids.

Silver nitrate solution can be used to distinguish between propanoyl chloride and 1-chloropropane.

Give the observations you would expect when a few drops of silver nitrate solution are added to separate samples of propanoyl chloride and 1-chloropropane.

Observation with propanoyl chloride

Observation with 1-chloropropane

This question is about an organic synthesis.

Name the mechanism in Step 1.

State the reagent(s) used for Step 1.

Name of mechanism

State the reagent(s) used for Step 4.

Outline the mechanism for Step 4.

Mechanism

In which conversion does a nucleophile attack the organic reactant?

What is the product when 3-methylbutan-2-one reacts with acidified KCN?

This question is about intermediates in reaction mechanisms.

Figure 3 shows an intermediate formed in the first step of a nucleophilic addition–elimination mechanism.

Figure 3

Complete Figure 3 to show the structures of the two reactant species with curly arrows and relevant lone pairs of electrons involved in the formation of the intermediate.

Draw curly arrows and relevant lone pairs of electrons on the intermediate to show how the final products are formed.

Figure 4 shows an intermediate formed in the first step of a reaction mechanism of methylbenzene.

Complete Figure 4 to show the reactant species and any curly arrows involved in the formation of the intermediate.

Draw a curly arrow on the intermediate to show how the product is formed.

Give the name of the reaction mechanism.

Name of mechanism

Figure 5 shows the reactant species involved in the first step of a mechanism.

Figure 5

Complete Figure 5 to show the structure of the intermediate formed with curly arrows involved in its formation.

Give the name of the reaction mechanism.

Name of mechanism

A student plans a series of chemical tests to confirm the identities of four organic

This is the student’s method.

To separate test tubes containing samples of each liquid:

Test 1 add potassium dichromate(VI) solution and warm gently

Test 2 add Fehling’s solution and cool in iced water

Test 3 add sodium hydrogencarbonate solution and test any gas produced with a lighted splint

Test 4 add bromine water and shake at room temperature.

Identify the missing reagent needed in Test 1.

In addition to the missing reagent in Test 1, there is a mistake in the method for two of the other tests.

State the two mistakes.

Suggest how each of the mistakes should be corrected.

The missing reagent is added and the mistakes are corrected.

Identify the liquid(s), J, K, L and M, that would react in each test.

State the expected observation for each reaction.

Liquid(s) that react in Test 1

Expected observation

Liquid(s) that react in Test 2

Expected observation

Liquid(s) that react in Test 3

Expected observation

Liquid(s) that react in Test 4

Expected observation

Figure 10 shows the apparatus that is used to separate a mixture of liquids K and M using fractional distillation.

Suggest labels that should be added to positions S, T and U in Figure 10.

Explain why fractional distillation is preferred to simple distillation to separate liquids K and M.

Consider this reaction scheme.

Which step is shown with a correct reagent and a correct condition?

An acidified solution of butanone reacts with iodine as shown.

Draw the displayed formula for CH₃CH₂COCH₂I

Give the name of CH₃CH₂COCH₂I

Displayed formula

The rate equation for the reaction is

Table 1 shows the initial concentrations used in an experiment.

The initial rate of reaction in this experiment is 1.45×10⁻⁴ mol dm⁻³ s⁻¹

Calculate the value of the rate constant, k, for the reaction and give its units.

Calculate the initial rate of reaction when all of the initial concentrations are halved.

An experiment was done to measure the time, t, taken for a solution of iodine to react completely when added to an excess of an acidified solution of butanone.

Suggest an observation used to judge when all the iodine had reacted.

The experiment was repeated at different temperatures. Figure 1 shows how varied with temperature for these experiments.

Describe and explain the shape of the graph in Figure 1.

Deduce the time taken for the reaction at 35^oC

For a different reaction, Table 2 shows the value of the rate constant at different temperatures.

This equation can be used to calculate the activation energy, E_a

Calculate the value, in kJ mol⁻¹, of the activation energy, E_a

The gas constant, R = 8.31 J K⁻¹mol⁻¹

Name and outline the mechanism for the reaction of butanone with KCN followed by dilute acid.

Name of mechanism

Outline of mechanism

Which type of reaction is not involved in this reaction sequence?

Which pair of reagents does not produce ethanol?

This question is about ketones.

Solution X reacts with liquid ketones to form a crystalline solid.

This reaction can be used to identify a ketone if the crystalline solid is separated, purified by recrystallisation, and the melting point determined.

Describe how the crystalline solid is separated and purified.

Propanone (CH₃COCH₃) reacts with the weak acid HCN to form a hydroxynitrile.

This hydroxynitrile is usually made by reaction of propanone with KCN followed by dilute acid, instead of with HCN

State the hazard associated with the use of KCN

Suggest a reason, other than safety, why KCN is used instead of HCN.

Why KCN is used

Outline the mechanism for the reaction of propanone with KCN followed by dilute acid.

This question is about the structural isomers shown.

Identify the isomer(s) that would react when warmed with acidified potassium dichromate(VI).

State the expected observation when acidified potassium dichromate(VI) reacts.

Expected observation

State the type of structural isomerism shown by isomers P, Q, R and S.

Describe fully how infrared spectra can be used to distinguish between isomers R, S and T. Use data from Table A in the Data Booklet in your answer.

State why mass spectrometry using electrospray ionisation is not a suitable method to distinguish between the isomers.

State the type of reaction in step 1.

Identify the reagent(s) and conditions needed for step 1.

State the name of the mechanism for the reaction in step 2.

Identify the inorganic reagent needed for step 2.

Name the organic product of step 2.

Name of mechanism

Name of organic product

The organic product of step 2 is reacted with concentrated sulfuric acid in step 3.

Outline the mechanism for step 3.

Draw the repeating unit of polystyrene.

Aqueous NaBH₄ reduces aldehydes but does not reduce alkenes.

Show the first step of the mechanism of the reaction between NaBH₄ and 2-methylbutanal. You should include two curly arrows.

Explain why NaBH₄ reduces 2-methylbutanal but has no reaction with 2-methylbut-1-ene.

First step of mechanism

A student attempted to reduce a sample of 2-methylbutanal but added

Give the reagent and observation for the chemical test.

Ethanal reacts with potassium cyanide, followed by dilute acid, to form 2-hydroxypropanenitrile.

Name the mechanism for the reaction between potassium cyanide and ethanal.

The 2-hydroxypropanenitrile formed by the reaction in question 04.1 is a mixture of equal amounts of two isomers.

State the name of this type of mixture.

Explain how the structure of ethanal leads to the formation of two isomers.

Draw 3D representations of the two isomers to show the relationship between them.

3D representations

2-Hydroxypropanenitrile can be used in the synthesis of the monomer,

Suggest a suitable reagent and conditions for the conversion of 2-hydroxypropanenitrile into acrylonitrile.

Draw a section of the polymer polyacrylonitrile, showing three repeating units.

How many structural isomers with the molecular formula C₅H₁₀O react with Tollens’

Give the IUPAC name of CH₃CH₂CH₂CH₂CH(OH)CN

Describe how you would distinguish between separate samples of the two

Explain why the reaction produces a racemic mixture.

An isomer of CH₃CH₂CH₂CH₂CHO reacts with KCN followed by dilute acid to form a compound that does not show stereoisomerism.

Draw the structure of the compound formed and justify why it does not show stereoisomerism.

Structure

Justification

You are provided with samples of each of the four compounds.

Describe how you could distinguish between all four compounds using the minimum number of tests on each compound.

You should describe what would be observed in each test.