OCR A-Level Chemistry Synthesis and analytical techniques (02), June 2018: Question 6

1 mark · Medium difficulty · Multiple Choice

Determine the number of peaks in the 1H NMR spectrum of HOOCCH2CHOHCH2COOH.

Practise this question

Question

Multiple choice question 6 asking for the number of peaks in the 1H NMR spectrum of HOOCCH2CHOHCH2COOH, with options A (3), B (4), C (5), and D (6), an answer box, and [1] mark allocation at the bottom right.
Question text

6 What is the number of peaks in the 1H NMR spectrum of HOOCCH CHOHCH COOH?

A 3

B 4

C 5

D 6

Your answer

[1]

Mark scheme

Show the mark scheme The mark scheme table shows question number 6, correct answer B, awarding 1 mark, with an allow note for 4 corresponding to the number of peaks in the NMR spectrum.

6 B 1 ALLOW 4 (This is the number of peaks in the NMR spectrum)

How to answer it

1H NMR Spectrum Analysis: Identifying Environment Count

What this question tests

This question assesses your ability to interpret molecular symmetry and identify the number of unique proton (¹H) chemical environments in an organic molecule to determine the number of peaks in a high-resolution ¹H NMR spectrum.

Question 6 Multiple Choice [1 Mark]

Determining Number of ¹H NMR Environments

Molecule: HOOCCH₂CHOHCH₂COOH

✅ Correct Answer

B: 4

There are 4 unique carbon-hydrogen environments due to the symmetrical structure of the molecule (citramalic or malic acid derivative backbone).

💡 Key Knowledge

  • Each chemically non-equivalent proton environment produces a separate peak in a ¹H NMR spectrum.
  • Planes of symmetry within a molecule make protons on opposite sides equivalent.
  • Exchangeable protons (like -OH and -COOH) also give individual peaks.

🧠 Exam Technique

Redraw condensed structural formulas symmetrically to spot mirror planes:

HOOC - CH₂ - CH(OH) - CH₂ - COOH

Notice the left-hand -CH₂-COOH is mirrored by the right-hand -CH₂-COOH .

❌ Common Errors

  • Counting splitting instead of environments: Mistaking high-resolution splitting patterns (multiplets) for the total number of environments.
  • Ignoring symmetry: Treating both -CH₂- groups as completely independent, leading to an incorrect total of 6 peaks.
Step-by-step breakdown of environments:
  1. Environment 1: -COOH proton (1 environment for both identical carboxylic acid groups due to symmetry).
  2. Environment 2: -CH₂- protons (Both -CH₂- groups are equivalent because of the central CH(OH) plane of symmetry).
  3. Environment 3: -CH(OH)- CH proton (1 unique carbon-attached proton on the central chiral carbon).
  4. Environment 4: -OH alcohol proton (1 peak for the hydroxyl group hydrogen).

Total number of environments = 4.

Topics

Module 6: Organic chemistry and analysis · 6.3 Analysis

Question and mark scheme from the OCR A-Level Chemistry examination, Synthesis and analytical techniques (02), June 2018. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.