IB DP Chemistry - R3.4.1 Nucleophiles - Study Notes - New Syllabus - 2026, 2027 & 2028

Reactivity 3.4.1 — Nucleophiles

 A species that donates a pair of electrons to form a covalent bond with an electrophile. Nucleophiles are electron-rich and are attracted to electron-deficient species (electrophiles). By definition, nucleophiles are also Lewis bases, since they act as electron-pair donors.

Key characteristics of nucleophiles:

• Possess a lone pair of electrons or a π-bond
• Are either negatively charged or neutral with a region of high electron density
• Can initiate a reaction by attacking a positively charged or electron-deficient center

Common nucleophiles:

• \( \text{OH}^- \) (hydroxide ion)
• \( \text{CN}^- \) (cyanide ion)
• \( \text{NH}_3 \) (ammonia)
• \( \text{H}_2\text{O} \) (water)
• \( \text{Cl}^- \), \( \text{Br}^- \), \( \text{I}^- \) (halide ions)

Types of nucleophiles:

• Negatively charged: These include anions with lone pairs. For example, \( \text{OH}^- \), \( \text{CN}^- \), \( \text{Cl}^- \)
• Neutral: Molecules like \( \text{NH}_3 \), \( \text{H}_2\text{O} \), or alcohols where lone pairs are present on atoms like O or N

Mechanism Note:

Nucleophiles are the reactants that attack the electrophilic center (usually a carbon bonded to a leaving group) in substitution or addition reactions.

Identifying a nucleophile in a chemical reaction:

Look for species that:

• Have lone pairs of electrons (e.g., N, O atoms)
• Are negatively charged or polarised
• Are drawn to partial positive charges (especially δ⁺ C atoms in polar bonds)