OCR A-Level Chemistry AS Breadth in chemistry (01), November 2020: Question 19

1 mark · Easy difficulty · Multiple Choice

Identify the correct description of a nucleophile in terms of electron pairing and attraction.

Practise this question

Question

A multiple choice question asking which row describes a nucleophile, with options A to D presenting combinations of electron pair donor/acceptor and attraction to high/low electron density. A table gives four rows: A (electron pair donor, attracted to high electron density), B (electron pair donor, attracted to low electron density), C (electron pair acceptor, attracted to high electron density), and D (electron pair acceptor, attracted to low electron density).
Question text

19 Which row describes a nucleophile?

A electron pair donor attracted to high electron density

B electron pair donor attracted to low electron density

C electron pair acceptor attracted to high electron density

D electron pair acceptor attracted to low electron density

Your answer [1]

Mark scheme

Show the mark scheme The mark scheme indicates that the correct answer for question 19 is B.

19 B 1 1.2

How to answer it

Defining Nucleophiles

What this question tests

This question tests your core definition and understanding of reaction terminology in organic chemistry—specifically distinguishing between nucleophiles and electrophiles regarding electron-pair movement and electrostatic attraction.

Question 19

Exam Breakdown

✅ Correct Answer: Row B

A nucleophile is an electron pair donor that is attracted to areas of low electron density (positive charge or partial positive charge).

💡 Key Knowledge

  • Nucleo-phile: Means "nucleus-loving". Nuclei are positive, so they love negative things or electron pairs.
  • Electron Pair Donor: Nucleophiles use a lone pair of electrons to form a new covalent bond (e.g., OH⁻, NH₃, CN⁻).
  • Low Electron Density: Because they are electron-rich, they are naturally attracted to electron-deficient sites (δ⁺ carbons).

🧠 Exam Technique

  • Break down multi-part definitions into two separate checks: What do they do with electrons? and Where are they attracted?
  • Eliminate rows systematically: Rule out "electron pair acceptor" immediately since acceptors are electrophiles.

❌ Common Errors

  • Confusing nucleophiles with electrophiles (electrophiles accept electron pairs and are attracted to high electron density).
  • Assuming a species attracted to high electron density must be negative (students often mix up electrostatic attraction with the species' own charge).
Mark Scheme Allocation: 1 mark available for selecting option B. Examiner reports note this is a straightforward recall item, but confusion between nucleophile and electrophile definitions frequently costs students marks in longer mechanisms.

Topics

Module 4: Core organic chemistry · 4.1 Basic concepts and hydrocarbons

Question and mark scheme from the OCR A-Level Chemistry examination, AS Breadth in chemistry (01), November 2020. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.