OCR A-Level Chemistry Synthesis and analytical techniques (02), June 2023: Question 13

1 mark · Easy difficulty · Multiple Choice

Identify which of the given organic structures are aliphatic compounds from a selection of three numbered structures.

Practise this question

Question

A multiple choice question asking which compound(s) is/are aliphatic. Structure 1 is a branched alkane chain, structure 2 is a cyclohexene ring with an ethyl group attached, and structure 3 is a benzene ring. Four multiple choice options are provided: A (1, 2 and 3), B (Only 1 and 2), C (Only 2 and 3), and D (Only 1), along with an answer box.
Question text

13 Which compound(s) is/are aliphatic?

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

Your answer

[1]

Mark scheme

Show the mark scheme The mark scheme indicates that the correct answer for question 13 is option B, worth 1 mark.

13 B 1 AO1.2

How to answer it

Identifying Aliphatic Compounds

OCR A-Level Chemistry • Multiple Choice Question

What this question tests

This question assesses your ability to recall and apply the definition of aliphatic versus aromatic organic compounds. It tests chemical nomenclature and structural recognition across straight-chain, branched, cyclic non-aromatic, and aromatic hydrocarbon systems (AO1.2).

Question 13 Breakdown

Evaluating the Options

✅ Correct Answer: B (Only 1 and 2)

Compound 1 is a branched, non-cyclic alkane (aliphatic). Compound 2 is a cyclic alkene (alicyclic, which falls under the broader category of aliphatic). Therefore, both 1 and 2 are aliphatic.

💡 Key Knowledge: Aliphatic vs Aromatic

  • Aliphatic compounds: Compounds containing carbon and hydrogen joined in straight chains, branched chains, or non-aromatic rings (alicyclic).
  • Aromatic compounds: Compounds containing a benzene ring (delocalised pi system conforming to Huckle's rule, represented by a circle inside a 6-membered ring).

🧠 Exam Technique

Evaluate each structure systematically one by one:

  • Structure 1: Open chain with branching. Definitely aliphatic.
  • Structure 2: Ring structure with a double bond, but no benzene ring. This is alicyclic (and thus aliphatic).
  • Structure 3: Classic kekulé/delocalised representation of benzene. This is aromatic, not aliphatic.

❌ Common Errors

  • Assuming any ring structure is aromatic (mistaking compound 2 for being aromatic just because it is cyclic). Remember: rings without delocalised benzene systems are alicyclic , which are classified as aliphatic.
  • Forgetting that saturated and unsaturated non-aromatic chains/rings both belong to the aliphatic family.
Mark Scheme Allocation: 1 mark awarded for selecting B.

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), June 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.