AP | A-Level | IB | NCERT 11 + 12 – FREE NOTES, RESOURCES AND VIDEOS!
S1.1 - Introduction to the particulate nature of matter S1.2 - The nuclear atom S1.3 - Electron configurations S1.4 - Counting particles by mass - The mole S1.5 - Ideal gases S2.1 - The ionic model S2.2 - The covalent model S2.3 - The metallic model S2.4 - From models to materials S3.1 - The periodic table - Classification of elements S3.2 - Functional groups - Classification of organic compounds R1.1 - Measuring enthalpy changes R1.2 - Energy cycles in reactions R1.3 - Energy from fuels R1.4 - Entropy and spontaneity AHL R2.1 - How much? The amount of chemical change R2.2 - How fast? The rate of chemical change R2.3 - How far? The extent of chemical change R3.1 - Proton transfer reactions R3.2 - Electron transfer reactions R3.3 - Electron sharing reactions R3.4 - Electron-pair sharing reactions

R3.4 - Electron-pair sharing reactions

3.4.1 Nucleophilic 3.4.2 Nucleophilic Substitution Reaction 3.4.3 Electrolytic Fission and Ionic Formation 3.4.4 Electrophilic 3.4.5 Electrophilic Addition to Alkenes 3.4.6 Lewis Acids and Bases (AHL) 3.4.7 Lewis Acid-Base Reaction and Co-ordinate Bonds (AHL) 3.4.8 Complex Ions and Ligand Co-coordination (AHL) 3.4.9 SN1 and SN2 Reaction (AHL) 3.4.10 Leaving Group and Substitution (AHL) 3.4.11 Electrophilic Addition of Alkenes (AHL) 3.4.12 Major Product of Addition Reaction (AHL) 3.4.13 Electrophilic Substitution of Benzene (AHL)

Nucleophilic Substitution Reactions

Specification Reference R3.4.2

Quick Notes

  • In a nucleophilic substitution reaction, a nucleophile donates an electron pair to a carbon atom bonded to a leaving group.
  • A new bond forms as the old bond breaks, removing the leaving group.
  • The reaction involves electron pair movement, shown with curly arrows.
  • Typical leaving groups include halide ions like Cl, Br, I.
  • Common nucleophiles: OH, CN, NH3.
  • Nucleophilic substitution is common in halogenoalkane reactions.

Full Notes

In a nucleophilic substitution reaction, a nucleophile donates an electron pair to form a new bond, as another bond breaks producing a leaving group.

Overview of the Reaction

IB Chemistry diagram showing nucleophile attacking carbon bonded to a leaving group.

The nucleophile attacks the carbon atom that is bonded to the leaving group, forming a new covalent bond and displacing the leaving group.

Mechanism

Nucleophilic substitution can be represented using a curly arrow mechanism, where each full arrow shows the movement of an electron pair.

The arrow starts from the electron source (typically a lone pair or bond) and points to where the electrons go – forming or breaking bonds.

One common such mechanism is the SN2 pathway. This occurs in primary and some secondary halogenoalkanes, shown below.

IB Chemistry curly arrow mechanism for nucleophilic substitution reaction.
  1. Curly arrow from nucleophile to δ+ carbon.
  2. Curly arrow from C–X bond to halogen (X leaves).
  3. New bond forms between nucleophile and carbon.

For Example:Halogenoalkane with OH

IB Chemistry nucleophilic substitution example showing halogenoalkane hydrolysing to alcohol with aqueous NaOH.

Reagent: Aqueous NaOH/KOH.
Conditions: Warm, reflux.

Summary