OCR A-Level Chemistry AS Breadth in chemistry (01), November 2021: Question 17

1 mark · Medium difficulty · Multiple Choice

Identify the systematic name of the given organic compound containing both an alcohol and an alkene functional group.

Practise this question

Question

Multiple choice question 17 asks for the systematic name of an organic compound shown as a skeletal structure. The molecule features a six-carbon chain containing a secondary alcohol group (-OH) and a double bond, with a methyl branch. Four options are provided: A, 3-methylhex-5-en-4-ol; B, 4-methylhex-1-en-3-ol; C, 2-ethylpent-4-en-3-ol; D, 4-ethylpent-1-en-3-ol.
Question text

17 What is the systematic name of the compound below?

OH

A 3-methylhex-5-en-4-ol

B 4-methylhex-1-en-3-ol

C 2-ethylpent-4-en-3-ol

D 4-ethylpent-1-en-3-ol

Your answer [1]

Mark scheme

Show the mark scheme The mark scheme indicates that the correct answer for question 17 is B.

17 B 1 AO1.2

How to answer it

Systematic IUPAC Nomenclature of Alkenols

What this question tests

This question assesses your ability to apply IUPAC naming rules to organic molecules containing multiple functional groups (specifically alkenes and alcohols). You must correctly identify the longest continuous carbon chain containing both functional groups, number the chain from the end that gives the principal functional group (the alcohol) the lowest possible locant, and assemble the prefix and suffix components alphabetically and numerically in the correct order.

Question 17

Determining the Systematic Name

✅ Correct Answer: B

4-methylhex-1-en-3-ol

Option B is the correct IUPAC name because it correctly identifies a 6-carbon principal chain containing both the double bond and the hydroxyl group, prioritises the alcohol for the lowest possible carbon numbering (C-3), and lists substituents in alphabetical order.

💡 Key Knowledge

  • Principal Functional Group: Alcohols (-ol) take priority over alkenes (-ene) for the lowest locant number.
  • Chain Selection: The longest carbon chain must contain both carbons of the alkene double bond and the carbon attached to the -OH group.
  • Alphabetical Order: Substituents (like methyl) are written alphabetically, ignoring numerical prefixes (e.g., di-, tri-).

🧠 Exam Technique

  • Trace both possible numbering directions from left-to-right and right-to-left to find which gives the alcohol group the smaller number.
  • Cross out incorrect options systematically by checking for common IUPAC rule violations (like misidentifying the main chain length).

❌ Common Errors

  • Numbering from the wrong end: Starting from the right gives the alcohol at C-4 instead of C-3 (leading to incorrect options like A).
  • Mistaking alkyl branches: Mistaking an ethyl group branching off for part of the main chain, leading to pentane stems instead of hexane (options C and D).
Examiner Commentary & Mark Breakdown: This is an AO1.2 recall and application question worth [1] mark. Top-level responses quickly recognised that the longest continuous chain containing the functional groups has 6 carbons (a hexane derivative), ruling out pentane options C and D immediately. Numbering from right-to-left gives the -OH group carbon-3, confirming B as the definitive correct choice.

Topics

Module 4: Core organic chemistry · Module 6: Organic chemistry and analysis · 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), November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.