OCR A-Level Chemistry Unified chemistry (03), June 2023: Question 3
6 marks · Hard difficulty · Extended Response
Describe the type of stereoisomerism shown by compound A and suggest three reactions for each of its functional groups, showing stereoisomers, reagents, conditions, and product structures.
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Question text
A chemist is investigating compound A, shown below, as a potential organic intermediate.
O
OH
CN
Compound A
Describe the type of stereoisomerism shown by compound A and suggest three reactions of
compound A, one for each of the three functional groups using reagents of your choice.
In your answer, show stereoisomers of compound A, your chosen reactants and conditions, and
the structures for the organic products produced.
Mechanisms and equations are not required. [6]
Additional answer space if required.
Mark scheme
Show the mark scheme
Question Answer Marks AO Guidance
element
3 Please refer to the marking instructions on page 6 of this 6 AO3.1 CHECK TOP OF QUESTION FOR RESPONSES
mark scheme for guidance on how to mark this question. 3 ------------------------------------------------------------
Indicative scientific points may include:
Level 3 (5–6 marks) AO3.2 Stereoisomerism
Suggests ALL of the following 3 • Optical isomerism identified with
• Reagents and conditions for 3 functional groups description: e.g. chiral centre
• Products for 3 functional groups /non-superimposable mirror images
• Optical isomerism with description and 3D optical • 3D Optical isomers drawn, e.g.
isomers shown
There is a well-developed line of reasoning which is clear and
logically structured.
The information presented is relevant and substantiated.
Level 2 (3–4 marks)
Suggests two of the following
• Reagents and conditions for 2 functional groups Description is subsumed in 3D diagrams
• Products for 2 functional groups Reactions of ketone/carbonyl e.g.
• Optical isomerism with description
OR an attempt to show 3D optical isomers NaBH4
There is a line of reasoning presented with some structure. OH
The information presented is relevant and supported by some
evidence.
OH
Level 1 (1–2 marks)
Suggests two of the following CN
• Reagents and conditions for 1 functional group
• Products for 1 functional group HCN OR CN–/H+ (e.g. NaCN/H+)
• Identifies optical isomerism with description
HO CN
OR an attempt to show 3D optical isomers
There is an attempt at a logical structure with a line of reasoning.
The information is in the most part relevant. OH
0 marks No response or no response worthy of credit. CN
element
Key points to check Reactions of –OH, e.g.
CHECK TOP OF QUESTION for responses H+/Cr O 2– OR H SO /K Cr O reflux
27 2 4 2 2 7
IGNORE CONNECTIVITY O O
in 3D isomer structures
OH
• IGNORE bond angles
• Wedges needed CN
• ALLOW
H+/Cr O 2– OR H SO /K Cr O distil
27 2 4 2 2 7
O
O
Some responses will not fit into this exact pattern and a CN
best-fit match may be needed
NaBr/KBr/Br– AND acid/H+ OR HBr
Clear communication O
Focus on
• Clear diagrams of 3D optical isomers
• Diagrams of unambiguous structures X
• Reagents and functional group formed are linked
CN
X = halogen
• Communication is more a general feel for the quality of
the responses. +
Acid/H (catalyst) (e.g. H2SO4)
O
Slips and minor errors in structures
• Do not penalise the odd slip or omission, e.g.
An extra C in a chain; a C short in a chain,
C shown instead of CH2 or skeletal
• You need to judge the extent of any slip based on the CN
whole response. Remember that each candidate
response is unique.
element
Reactions of C–CN, e.g.
H2 AND metal catalyst e.g. Ni, Pt, Pd
O
OH
NH2
H+/H O e.g. HCl(aq) or H SO (aq)
22 4
O
OH
COOH
OTHER REAGENTS, CONDITIONS AND
PRODUCTS
e.g. LiAlH4 as reagent
Check with Team Leader
How to answer it
Organic Synthesis and Stereoisomerism of Compound A
What this question tests
This multi-step 6-mark question assesses your ability to identify stereoisomerism (specifically optical isomerism with 3D tetrahedral representations), recognise multiple functional groups within a single organic molecule (ketone, primary alcohol, and nitrile), and recall specific reagents, conditions, and resulting organic products for each functional group's reactions.
Question Overview & Mark Allocation
This is a Level of Response (LoR) question marked out of 6 marks, using three response tiers (Level 1: 1-2 marks, Level 2: 3-4 marks, Level 3: 5-6 marks). To achieve Level 3, you must correctly address all three functional groups, provide valid reagents/conditions and products for each, and accurately describe and draw 3D optical isomers.
💡 Key Knowledge: Functional Groups in Compound A
- Ketone: Carbonyl group (C=O) bonded to two carbon atoms.
- Primary Alcohol: Hydroxyl group (-OH) attached to a CH₂ group.
- Nitrile: Cyanide group (-C≡N).
🧠 Exam Technique for 6-Mark Synthesis
Break your answer down clearly into sections. Label your stereoisomerism description and then dedicate clear bullet points or sub-headings to each of the three functional group reactions, stating both the reagent(s) and the structure of the organic product.
Part 1: Stereoisomerism (Optical Isomerism)
✅ Correct Answer & Description
Compound A exhibits optical isomerism (a type of stereoisomerism). This occurs because it contains a chiral centre (an asymmetric carbon atom bonded to four different groups). The chiral carbon is the CH group bonded to the -CN group.
3D Representation: You must draw two non-superimposable mirror images using 3D bonds (solid lines for in-plane, wedges for coming out, and hatched/dashed bonds for going into the page).
❌ Common Errors & Examiner Pitfalls
- Failing to use proper 3D bond conventions (wedges and dashes are mandatory to show tetrahedral arrangement around the chiral centre).
- Confusing optical isomerism with E/Z (geometrical) isomerism.
- Selecting the wrong carbon as the chiral centre (e.g., trying to use the CH₂-OH carbon, which has two identical hydrogens).
Part 2: Reactions of the Three Functional Groups
You must choose one reaction for each of the three functional groups found in compound A. Below are the standard, accepted routes from the mark scheme.
1. Reactions of the Ketone (C=O)
Option A (Reduction):
Reagent/Condition: NaBH₄ (or LiAlH₄ )
Product: Secondary alcohol formed where the C=O becomes a CH-OH group.
Option B (Nucleophilic Addition):
Reagent/Condition: HCN or NaCN / H⁺
Product: Hydroxynitrile.
2. Reactions of the Primary Alcohol (-OH)
Option A (Oxidation):
Reagent/Condition: K₂Cr₂O₇ / H⁺ under reflux
Product: Carboxylic acid (-COOH).
Option B (Substitution):
Reagent/Condition: NaBr and H₂SO₄ (forms HBr in situ)
Product: Haloalkane (-Br replacing -OH).
3. Reactions of the Nitrile (-C≡N)
Option A (Reduction):
Reagent/Condition: H₂ with Ni catalyst (or LiAlH₄ )
Product: Primary amine (-CH₂NH₂).
Option B (Hydrolysis):
Reagent/Condition: Aqueous acid e.g. H⁺ / H₂O (or HCl(aq) ) under reflux
Product: Carboxylic acid (-COOH).
Topics
Module 6: Organic chemistry and analysis · Module 4: Core organic chemistry · 6.1 Aromatic compounds, carbonyls and acids · 6.2 Nitrogen compounds, polymers and synthesis · 4.2 Alcohols, haloalkanes and analysis
Question and mark scheme from the OCR A-Level Chemistry examination, Unified chemistry (03), June 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.