Edexcel A-Level Chemistry Paper 2, November 2021: Question 3
1 mark · Medium difficulty · Multiple Choice
Identify the systematic IUPAC name including E/Z stereochemistry for tiglic acid given its skeletal structure.
Practise this questionQuestion
Question text
3 What is the systematic name for tiglic acid?
O
OH
tiglic acid
A E-2-methylbut-2-enoic acid
B Z-2-methylbut-2-enoic acid
C E-3-methylbut-2-enoic acid
D Z-3-methylbut-2-enoic acid
(Total for Question 3 = 1 mark)
Mark scheme
Show the mark scheme
Question
Answer Mark
Number
3 The only correct answer is A (E-2-methylbut-2-enoic acid) (1)
B is incorrect because the two high priority groups are on opposite sides
C is incorrect because the methyl group is on carbon 2
D is incorrect because the two high priority groups are on opposite sides and the methyl group is on carbon 2
How to answer it
Systematic Naming & E-Z Isomerism
What this question tests
This question assesses your ability to apply IUPAC nomenclature rules to organic molecules containing functional groups, locate substituents using lowest-number numbering rules, and determine stereoisomerism using Cahn-Ingold-Prelog (CIP) priority rules for E-Z descriptors.
Determining the Systematic Name of Tiglic Acid
✅ Correct Answer
A: E -2-methylbut-2-enoic acid
💡 Key Knowledge
- Principal Functional Group: The carboxylic acid group ( -COOH ) takes highest priority and dictates carbon-1.
- Carbon Chain: The longest carbon chain containing the double bond has 4 carbons (but-2-enoic acid).
- Substituent Position: A methyl group ( -CH₃ ) is attached to carbon-2.
- Stereoisomerism ( E / Z ): Determined using CIP priority rules across the C=C double bond.
🧠 Exam Technique
Break down naming questions systematically:
- Find the principal functional group to get the suffix ( -oic acid ).
- Number the chain from the carboxylic acid carbon to give the double bond and branches the lowest possible numbers.
- Identify the position and name of side chains (methyl at carbon-2).
- Assign E or Z by splitting the double bond vertically and comparing atomic numbers of attached groups.
❌ Common Errors & Distractor Analysis
- Option B ( Z -2-methylbut-2-enoic acid): Incorrect stereochemistry; high-priority groups are actually on opposite sides ( E ).
- Option C ( E -3-methylbut-2-enoic acid): Misnumbered the carbon chain, incorrectly placing the methyl group at carbon-3.
- Option D ( Z -3-methylbut-2-enoic acid): Contains both errors (wrong position number and wrong E / Z assignment).
Topics
Organic Chemistry · Topic 6: Organic Chemistry I
Question and mark scheme from the Edexcel A-Level Chemistry examination, Paper 2, November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.