OCR A-Level Chemistry AS Breadth in chemistry (01), June 2024: Question 14

1 mark · Medium difficulty · Multiple Choice

Identify the correct IUPAC name for a given haloalcohol molecule containing a chlorine atom, a methyl branch, and an alcohol functional group.

Practise this question

Question

Multiple choice question 14 asks to name the compound shown in the skeletal-like structural formula. The structure has a Cl atom at the left end, a methyl group branching upwards, another methyl group branching downwards, and an OH group at the right end attached to a CH2. Four options A, B, C, and D provide different IUPAC names with varying locants and prefixes.
Question text

14 What is the name of the compound below?

Cl OH

A 1‑chloro‑1,2‑dimethylpropan‑3‑ol

B 2‑chloro‑3‑methylbutan‑4‑ol

C 3‑chloro‑2‑methylbutan‑1‑ol

D 3‑chloro‑2,3‑dimethylpropan‑1‑ol

Your answer [1]

Mark scheme

Show the mark scheme The mark scheme indicates that the correct answer for question 14 is C, worth 1 mark.

14 C 1

How to answer it

Naming Halogenoalcohols (IUPAC Nomenclature)

What this question tests

This question assesses your ability to apply IUPAC rules of organic nomenclature to a multi-functional group molecule. You must correctly identify the longest carbon chain, assign the principal functional group priority (alcohol over halogen), number the chain to give lowest locants, and list substituents alphabetically with correct prefixes and numbers.

Question 14

Determining the IUPAC Name

✅ Correct Answer

C: 3-chloro-2-methylbutan-1-ol

Mark Allocation: 1 mark for identifying option C.

💡 Key Knowledge (IUPAC Rules)

  • Principal Functional Group: The alcohol (-OH) group takes highest priority, giving the suffix -ol and carbon-1 closest to it.
  • Longest Carbon Chain: Tracing from the -OH carbon (C1) through the branch gives a continuous chain of 4 carbons (butane skeleton).
  • Alphabetical Order: Substituents are listed alphabetically ( chloro before methyl ), ignoring numerical prefixes like di- or tri-.

🧠 Exam Technique

  • Step 1: Find the suffix. The molecule contains an -OH on the end carbon, making it a butan-1-ol derivative (rules out options A and D).
  • Step 2: Number the main chain. Start numbering from the carbon attached to the -OH as carbon-1. Move along the longest carbon chain.
  • Step 3: Locate substituents. Carbon-2 has a methyl group ( -CH₃ ) attached, and carbon-3 has a chlorine atom ( -Cl ).

❌ Common Errors

  • Wrong Chain Length (Options A & D): Students often mistake the longest vertical/horizontal path for 3 carbons (propane) instead of tracing the 4-carbon chain.
  • Incorrect Numbering Direction (Option B): Numbering from the left end gives 2-chloro-3-methylbutan-4-ol , violating the rule that the principal functional group (-OH) must have the lowest possible number (1-ol, not 4-ol).
  • Incorrect Alphabetical Listing: Failing to place chloro before methyl in the name.

Topics

Module 4: Core organic chemistry · Module 2: Foundations in chemistry · 4.1 Basic concepts and hydrocarbons · 4.2 Alcohols, haloalkanes and analysis

Question and mark scheme from the OCR A-Level Chemistry examination, AS Breadth in chemistry (01), June 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.