OCR A-Level Chemistry Synthesis and analytical techniques (02), November 2021: Question 1
1 mark · Medium difficulty · Multiple Choice
Determine the number of structural isomers with the molecular formula C5H11Cl formed from the radical substitution reaction of 2-methylbutane with chlorine.
Practise this questionQuestion
Question text
1 2-Methylbutane is reacted with chlorine by radical substitution.
What is the number of structural isomers with the molecular formula C5H11Cl that could be
formed?
A 2
B 3
C 4
D 5
Your answer
[1]
Mark scheme
Show the mark scheme
Question Answer Marks AO element Guidance
1 C 1 AO2.1 ALLOW 4 (This is the number of structural isomers)
How to answer it
Radical Substitution and Structural Isomers
What this question tests
This question assesses your ability to apply knowledge of free radical substitution to alkanes, identify structural isomerism, and systematically analyze different carbon environments in a branched alkane chain.
Determining Monochlorination Isomers of 2-Methylbutane
✅ Correct Answer: C (4)
There are 4 possible structural isomers with the molecular formula C₅H₁₁Cl formed by replacing one hydrogen atom in 2-methylbutane with a chlorine atom.
💡 Key Knowledge
- 2-methylbutane structure: CH₃-CH(CH₃)-CH₂-CH₃
- Carbon environments: Look for chemically distinct hydrogen-bearing carbon atoms in the chain.
- There are 4 different carbon environments where a hydrogen can be substituted by chlorine.
🧠 Exam Technique
Systematically draw out the carbon skeleton and substitute a chlorine atom into every unique position one at a time. Rename each structure using IUPAC nomenclature to ensure you haven't duplicated any molecules or missed a positional isomer.
❌ Common Errors
Students often miscount carbon environments in branched chains or confuse structural isomerism with stereoisomerism (optical/E-Z). Remember, this question specifically asks for structural isomers.
Topics
Module 4: Core organic chemistry · 4.1 Basic concepts and hydrocarbons
Question and mark scheme from the OCR A-Level Chemistry examination, Synthesis and analytical techniques (02), November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.