Edexcel A-Level Chemistry Paper 2, June 2022: Question 8
14 marks · Hard difficulty · Open Response
Deduce NMR spectra peaks, molecular formula, constituent acids/alcohols, ester isomers, acylation equations, and compare acid/alkali hydrolysis methods for isoamyl and amyl acetate.
Practise this questionQuestion
Question text
8 Esters have many uses due to their characteristic aromas and often have common
names. For example, isoamyl acetate is referred to as banana oil and amyl acetate has
a scent similar to apples.
O O
O O
isoamyl acetate amyl acetate
(a) What is the number of peaks in a 13C NMR spectrum of isoamyl acetate and of
amyl acetate?
(1)
isoamyl acetate amyl acetate
A 5 6
B 6 6
C 6 7
D 7 7
(b) State the molecular formula of amyl acetate.
(1)
(c) Deduce the structural formula of the carboxylic acid that could be used to form
both isoamyl acetate and amyl acetate.
(1)
(d) Deduce the name of the alcohol that forms isoamyl acetate.
(1)
(e) Give the systematic name for amyl acetate.
(1)
(f ) The carboxylic acid used to make isoamyl acetate and amyl acetate can also be
used to make six further ester isomers. The structures of two of these esters,
A and B, are shown.
(i) Complete the skeletal*P67094RA01824*formulae ofthreeof the remaining esters.
Names are not required.
(3)
O O
O
O O
O
isoamyl acetate amyl acetate
O
O
O
O
ester A
O
O
O
O
ester B
(ii) Write an equation to show the formation of ester A from an acyl chloride and
an alcohol.
(2)
(g) Esters can be hydrolysed by heating under reflux with aqueous acid or alkali.
Compare and contrast these two methods of hydrolysis for amyl acetate.
(4)
… *P67094RA01924*
(Total for Question 8 = 14 marks)
Mark scheme
Show the mark scheme
Question
Answer Mark
Number
8(a) The only correct answer is C (6 ……. 7) (1)
A is not correct because there are six non-equivalent carbons in isoamyl acetate and seven in
amyl acetate
B is not correct because all carbons of amyl acetate generate their own peak in the spectrum
D is not correct because the two methyl groups on the branched chain are equivalent
Question
Answer Additional Guidance Mark
Number
8(b) (1)
• C7H14O2 Accept atoms in any order
Question
Answer Additional Guidance Mark
Number
8(c) (1)
• CH3COOH Allow displayed, skeletal or
combination of
Do not award molecular formula
Question
Answer Additional Guidance Mark
Number
8(d) Allow ‘methly’ for methyl (1)
• 3-methylbutan-1-ol Allow name with missing hyphens
Allow 3-methylbutane-1-ol
Allow 3-methylbut-1-anol
Allow 1-hydroxy-3-methylbutane
Do not allow 3-methylbut-1-ol
Ignore formulae even if incorrect
Question
Answer Additional Guidance Mark
Number
8(e) (1)
• pentyl ethanoate Allow pentanyl ethanoate
Question
Answer Additional Guidance Mark
Number
8(f)(i) Any three of the following four structures (3)
Accept formulae in any
order
(1) Award (2) if 3 correct
(1) (1) (1)
displayed/structural
formulae given
Award (1) if 2 correct
displayed/structural
formulae given
Question
Answer Additional Guidance Mark
Number
8(f)(ii) An equation that has Example of equation (2)
• ethanoyl chloride (1)
• alcohol
and ester+ HCl product (1)
Allow structural, displayed formulae in any combination
Ignore connectivity to OH except horizontal
Ignore state symbols even if incorrect
If molecular formulae used then allow (1) for correct equation
Allow (1) for a correct equation to form ester A from ethanoic acid
e.g.
CH3COOH + CH3CH(OH)CH2CH2CH3 ⇌ CH3COOCH(CH3) CH2CH2CH3 + H2O
Question
Answer Additional Guidance Mark
Number
8(g) An answer that makes reference to the following points: Points can be made in equations (4)
(similarity)
• both make the (same) alcohol / pentan-1-ol (1)
(differences)
• acid hydrolysis is reversible, alkaline hydrolysis is Accept acid hydrolysis is an
irreversible (1) equilibrium and alkaline hydrolysis
goes to completion
• acid hydrolysis produces the carboxylic acid/ ethanoic acid Allow just acid for carboxylic acid
and
alkaline hydrolysis produces the carboxylate / ethanoate Allow salt for carboxylate
(ion) (1)
• the acid is a catalyst and the alkali is a reactant (1) Allow the acid will be regenerated /not
used up but the alkali will be used up
Ignore references to rate differences
Ignore references to a need for the
product of alkaline hydrolysis to be
acidified which is different to acid
hydrolysis
(Total Question 8 = 14 marks)
How to answer it
Structure, Isomerism, and Hydrolysis of Esters
What this question tests
This question assesses your understanding of organic chemistry fundamentals specifically relating to esters: interpreting C-13 NMR spectra to count non-equivalent carbon environments, deriving molecular and structural formulas, applying IUPAC nomenclature rules, drawing structural/skeletal isomer permutations, writing acylation equations, and comparing acid vs. alkaline hydrolysis mechanisms.
C-13 NMR Environments
✅ Correct Answer
C (isoamyl acetate = 6, amyl acetate = 7)
💡 Key Knowledge
Each non-equivalent carbon atom in a molecule produces a distinct peak in a C-13 NMR spectrum. Symmetry reduces the number of peaks expected.
❌ Common Errors
Assuming branched chains automatically yield more peaks. In isoamyl acetate, the two methyl groups attached to the CH are chemically equivalent due to rotation/symmetry, reducing the expected carbon environments to 6.
Molecular Formula of Amyl Acetate
✅ Correct Answer
C₇H₁₄O₂ (Accept atoms in any order)
🧠 Exam Technique
Count carbons carefully from the skeletal structure (5 carbons in the pentyl chain + 2 carbons in the ethanoyl group = 7 carbons total). Ensure hydrogen counting accounts for all saturated chain terminals and methyl groups.
Carboxylic Acid Precursor
✅ Correct Answer
CH₃COOH (Ethanoic acid)
❌ Common Errors
Writing the molecular formula ( C₂H₄O₂ ) when a structural or displayed formula was required. The mark scheme explicitly states: Do not award molecular formula.
Alcohol Name for Isoamyl Acetate
✅ Correct Answer
3-methylbutan-1-ol
💡 Key Knowledge
Acceptable alternative IUPAC variations include 3-methylbutan-1-ol , missing hyphens, or alternative positional number styling ( 3-methylbut-1-ol ). Always prioritize rigorous IUPAC numbering starting from the alcohol carbon (-OH gets carbon 1).
Systematic Name for Amyl Acetate
✅ Correct Answer
pentyl ethanoate (Accept pentanyl ethanoate )
🧠 Exam Technique
Split the ester name mentally: the alkyl group attached to the single-bonded oxygen comes first (pentyl, derived from pentan-1-ol), followed by the carboxylate part derived from the acid (ethanoate).
Skeletal Formulae of Remaining Ester Isomers
✅ Correct Answer
Any 3 valid remaining structural/skeletal isomers of pentyl ethanoate (such as 2-methylbutyl ethanoate, 2,2-dimethylpropyl ethanoate, pentan-2-yl ethanoate, pentan-3-yl ethanoate, 3-methylbutyl ethanoate variations depending on structural prompts).
🧠 Exam Technique
Grading is tiered: Award (1) mark for 2 correct structures, and (2) or (3) marks for all 3 correct skeletal structures clearly drawn.
Acylation Equation
✅ Correct Answer
Ethanoyl chloride + respective alcohol forming Ester A + HCl
💡 Key Knowledge
Using acyl chlorides instead of carboxylic acids for esterification produces a high yield because the reaction goes to completion and releases steamy fumes of hydrogen chloride gas ( HCl ) rather than water.
Comparing Acid and Alkaline Hydrolysis
💡 Key Knowledge & Similarities
Both methods yield the same alcohol product ( pentan-1-ol ) when hydrolyzing amyl acetate.
🧠 Exam Differences (The Contrast)
- Reversibility: Acid hydrolysis is a reversible equilibrium reaction; alkaline hydrolysis goes to completion (irreversible).
- Organic Products: Acid hydrolysis produces a carboxylic acid ( ethanoic acid ), whereas alkaline hydrolysis produces a carboxylate salt ( ethanoate ion ).
- Role of Reagents: Hydrogen ions from the acid act as a catalyst (regenerated), whereas hydroxide ions from the alkali act as a direct reactant (consumed).
Topics
Organic Chemistry · Topic 17: Organic Chemistry II · Topic 18: Organic Chemistry III · Topic 19: Modern Analytical Techniques II · Topic 6: Organic Chemistry I
Question and mark scheme from the Edexcel A-Level Chemistry examination, Paper 2, June 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.