Organic Synthesis (OCR A Level Chemistry A): Exam Questions

An organic reaction scheme is shown below.

C₄H₈ C₄H₁₀O C₄H₈O C₄H₈O₂ 

State the IUPAC names of the four substances in the reaction scheme.

Classify the reactions in (a) and name a pair of reagents required in each step.

Give the reaction conditions for step 3.

Write the structural formula of an isomer of C₄H₁₀O that will not react according to step 2.

Outline how ethanal can be synthesised from ethane in three steps.

State the reaction conditions and reagents and name the type of reaction taking place.

The following reaction pathway is used to produce Compounds A and B, which when reacted together, form a branched ester molecule, Compound C. 

Suggest suitable reagents and conditions for the synthesis of Compound A via Step 1 and give the name for this type of reaction.

The ketone in part (a), must be converted to compound B to produce the ester.

i) Name the molecule that is produced from Step 2

ii) Name of the type of reaction that is involved in Step 2 and suggest suitable reagents and conditions for this step.

Draw the skeletal formula of the ester formed from the reaction scheme.

1-(3-Aminophenyl)ethanol can be synthesised according to the following three-step reaction scheme.

Step 1 involves a reaction at position 3 of the benzene ring of 1-phenylethan-1-one.

State the reaction type, including suitable reagents, for Step 1.

Step 2 involves changes to the ketone group.

State a suitable reagent for Step 2.

In Step 3 of the reaction scheme, compound C is heated with hydrochloric acid in the presence of a tin catalyst to form the final product, 1-(3-aminophenyl)ethanol. 

Explain why Step 3 is a reduction reaction.

Suggest a reaction scheme, using displayed formulae, that could be used to prepare a sample of propyl propanoate from one reactant. 

Conditions and reagents are not required.

One of the intermediates in the reaction scheme has a molecular mass of 74.0 g mol^-1.

i) State suitable reagents and conditions required to form this intermediate. 

ii) Describe how you could test that this intermediate has been formed.

Propanal and the intermediate (M_r = 74.0) in the reaction scheme are to be separated by distillation.

Explain which chemical will distil off first.

One of the intermediates in the reaction scheme has a molecular mass of 60.0 g mol^-1. 

i) State suitable reagents and conditions required to form this intermediate. 

ii) Describe how you could prove that this intermediate has been formed without reversing the reaction.

Aspirin is a medicine used to relieve pain and reduce fever.

A student prepares a sample of aspirin, HOOCC₆H₄OCOCH_3, from salicylic acid, HOOCC₆H₄OH.

The student makes aspirin by warming 7.5 g of salicylic acid with 15.0 cm³ of ethanoic anhydride, (CH₃CO)₂O, in the presence of concentrated sulfuric acid.

Write a balanced equation, using structural formulae, for this reaction.

The density of ethanoic anhydride is 1.10 g cm^–3.

Deduce whether the salicylic acid or ethanoic anhydride is in excess. 

The student transfers their hot solution into water and impure aspirin crystallises out as the water cools.

The student then purifies the aspirin by recrystallisation.

State the properties of a suitable solvent for recrystallisation. 

After recrystallisation, the student obtained 5.91 g of aspirin.

Calculate the student's percentage yield. 

This question is about the synthesis and purification of organic amines.

1-chloropropane is to be converted into 1-aminobutane.

Plan a two-stage synthetic route to achieve this conversion. In your answer, state the reagents and conditions for each stage and the structure of the intermediate compound.

A student starts with 5.50 g of 1-chloropropane.

The overall percentage yield for the conversion to 1-aminobutane is 42.0%.

Calculate the expected mass, in g, of 1-aminobutane produced. Give your answer to 3 significant figures.

A student prepares a sample of a liquid organic product from the reaction of an alcohol with concentrated hydrochloric acid.

The student obtains a crude liquid mixture containing the organic product, unreacted alcohol, and water. The organic product is immiscible with water.

Describe the essential practical procedure required to purify this crude liquid to obtain a pure sample of the organic product.
In your answer:

• Detail the use of a separating funnel and specific reagents for drying.

• Explain the purpose of each step in the purification.

This question is about organic synthesis and green chemistry.

Methyl phenyl ketone (phenylethanone) is used in the perfumery industry. It can be synthesised from benzene by the reaction with ethanoyl chloride, CH₃​COCl, in the presence of an aluminium chloride catalyst, AlCl₃.

Outline the mechanism for the formation of methyl phenyl ketone from benzene.

Your answer should include:

• An equation for the formation of the electrophile.

• Curly arrows, relevant dipoles, and the structure of the intermediate.

• An equation showing the regeneration of the catalyst.

After the reaction, the crude methyl phenyl ketone is a solid. It is purified by filtration under reduced pressure.

Draw a fully labelled diagram of the apparatus used for filtration under reduced pressure.

Ethyl ethanoate can be prepared by two different routes.

• Route 1: CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O

• Route 2:CH₃COCl + C₂H₅OH → CH₃COOC₂H₅ + HCl

i) Calculate the atom economy for the formation of ethyl ethanoate by Route 2.

(M_r values: CH₃​COCl = 78.5; C₂​H₅​OH = 46.0; CH₃​COOC_2​H₅​ = 88.0; HCl = 36.5).

[2]

ii) Suggest one reason why a chemical company might prefer Route 1 over Route 2, and one reason why they might prefer Route 2 over Route 1.

[2]

Shikimic acid is a cyclohexene derivative found in Japanese star anise and is used as a base for the synthesis of Tamiflu, an important influenza treatment. The structure of shikimic acid is shown below

Identify three functional groups found in shikimic acid and suggest how each may be identified.

Shikimic acid can be converted into other useful intermediates. A three step synthesis is shown below:

i) Give the reagents and conditions needed for steps 1, 2 and 3.

[3]

ii) State the type of reactions and mechanisms taking place.

[3]

Determine the mass of shikimic acid (M_r =174.15 g mol^-1) that must be used in step 1 to produce 10.0 g of compound P(M_r = 255.05 g mol^-1), assuming a yield of 65%.

The conversion of compound P to Q occurs in a single step and requires heating. Heating substances in the laboratory can be carried out using the apparatus below.

Give one reason why this apparatus would not be suitable.

This question is about a drug called mesalamine (also known as 5-aminosalicylic acid) that is used to treat bowel disease. It can be synthesised from salicylic acid, the chemical structure of which is shown below:

State the systematic IUPAC name for salicylic acid and deduce how many positional isomers are possible, giving their names and structures.

A possible two step synthesis of mesalamine is shown below.

Complete the flowchart showing the structures of compound B and mesalamine.

What reagents and conditions are needed to convert:

i) Salicylic acid into compound B?

[2]

ii) Compound B into mesalamine?

[3]

Give the structures of compound C and the compound D(repeat unit).

Chloroquine is antimalarial drug that was briefly trialed during the Covid-19 pandemic, but not found to be effective in treating SARS-CoV-2 infections. It can be synthesised from 4,7-dichloroquinoline. The structures of the two compounds are shown below.

Determine the molecular formula of 4,7-dichloroquinoline and chloroquine.

Deduce the type of reaction taking place and write the formula of the co-product of the reaction that converts 4,7-dichloroquinoline into chloroquine.

Organic molecules have to be highly purified for use as pharmaceutical drugs. Suggest how the purity of a sample of chloroquine can be determined after synthesis from 4,7-dichloroquinoline.

Ethyl 4-aminobenzoate, shown in Figure 1, is more commonly known as benzocaine. It is an ester based compound that is used medicinally as a local anaesthetic in pain relievers and cough drops.

Figure 1

One of the first industrial processes to manufacture benzocaine was the multi-step reaction shown in Figure 2.

Figure 2

The current cost of >99.7% pure benzene is around £10.00 per litre compared to > 99.5% pure methylbenzene at a cost of around £7.00 per litre.

Explain why it would be beneficial to start from methylbenzene instead of benzene in the manufacture of benzocaine. Your answer should not include economic considerations.

Concentrated sulphuric acid and concentrated nitric acid are used to form the nitronium ion required for step 2 of the reaction scheme, in part (a).

The following equilibrium is the first step in the formation of the nitronium ion.

H₂SO₄ + HNO₃ ⇋ HSO₄^- + H₂NO₃⁺

i) State the implications of this reaction in terms of the roles played by the acids. 

ii) Use your answer to part (i) to compare the strengths of the acids.

Give the reagents and conditions necessary for steps 4 and 5 of the reaction scheme shown in part (a).

A student suggests the reaction scheme shown in Figure 3 as an alternative to the original industrial reaction scheme shown in part (a) for the production of benzocaine.

Figure 3

i) State why the student’s reaction scheme is an improvement.

ii) Suggest why the student’s reaction scheme may not work.

A student is asked to prepare a sample of propyl propanoate using propanal.

Suggest a reaction scheme, using displayed formulae, that the student could use to prepare their sample of propyl propanoate.

Conditions and reagents are not required.

Use your answer from part (a) to help answer this question.

One of the intermediates in the reaction scheme, from part (a), has a molecular mass of 74.0 g mol-1.

i) Give the reagents and conditions required to form this intermediate.

ii) Describe how you could test that this intermediate has been formed.

Propanal and the intermediate (M_r = 74.0) in the reaction scheme, from part (a), are to be separated by distillation.

Explain which chemical will distill first.

Use your answer from part (a) to help answer this question.

One of the intermediates in the reaction scheme, from part (a), has a molecular mass of 60.0 g mol-1. 

i) Give the reagents and conditions required to form this intermediate.

ii) Describe how you could prove that this intermediate has been formed without reversing the reaction.

Propanone can be synthesised from 2-bromopropane according to the reaction scheme shown in Figure 1. 

Figure 1

Step 1 is not completed in acidic conditions.

i) Give the reagents and conditions for step 1.

ii) Outline the mechanism for step 1

Give the reagents and conditions for steps 2 and 3 of the reaction scheme in part (a).

Suggest one reaction to replace steps 1 and 2 in the part (a) reaction scheme.

To prepare a sample of ethanal, a student adapts the reaction scheme from part (a). The student’s adapted reaction scheme is shown in Figure 2.

Figure 2

Explain one improvement the student should make to their adapted reaction scheme.