AQA Mechanism Summary - A-Level Chemistry

Key Organic Mechanisms

Nucleophilic Substitution

• Halogenoalkanes with Aqueous Hydroxide Ions
• Halogenoalkanes with Cyanide Ions
• Ammonia forming Primary Amine
• Secondary and Tertiary Amines Formation
• Quaternary Ammonium Salt Formation

Elimination Reaction

• Halogenoalkanes with Ethanolic Hydroxide Ions

Electrophilic Addition

• Alkenes with Bromine
• Alkenes with Hydrogen Bromide
• Alkenes with Sulfuric Acid

Acid Catalysed Reactions

• Addition for Hydration of Ethene
• Elimination for Alcohols to Alkenes
  • Acid catalysts include concentrated ( \text{H}_2\text{SO}_4 ) or ( \text{H}_3\text{PO}_4 )

Free Radical Substitution

• Alkanes with Bromine
  • Essential condition: UV light
  • Steps: Initiation, Propagation, Termination

Detailed Mechanism Steps

Initiation

• ( \text{Br}_2 \rightarrow 2\text{Br}\cdot )

Propagation

• ( \text{CH}_3\text{CH}_2\cdot + \text{Br}_2 \rightarrow \text{CH}_3\text{CH}_2\text{Br} + \text{Br}\cdot )

Termination

• ( \text{CH}_3\text{CH}_2\cdot + \text{Br}\cdot \rightarrow \text{CH}_3\text{CH}_2\text{Br} )

Nucleophilic Addition-Elimination Mechanism

• Involves acyl chlorides and amines or alcohols

Electrophilic Substitution Mechanisms

Formation of Electrophile

• ( \text{HNO}_3 + 2\text{H}_2\text{SO}_4 \rightarrow \text{NO}_2^+ + 2\text{HSO}_4^- + \text{H}_3\text{O}^+ )

Reaction Conditions

• AlCl(_3) catalyst for reactions involving acyl chlorides

Reduction Reactions

• Using NaBH(_4) for reduction in nucleophilic addition
• Using LiAlH(_4) in ether for stronger reduction processes

Other Reactions

Esterification

• Alcohol and Carboxylic Acids with ( \text{H}_2\text{SO}_4 )

Hydration

• Uses concentrated ( \text{H}_3\text{PO}_4 ) or ( \text{H}_2\text{SO}_4 ) for hydration mechanisms

Reaction Summary for Aromatic Compounds

• Electrophilic Substitution with Conc. Nitric Acid and Sulfuric Acid
• Sn and HCl Reduction for Amine Formation

Additional Notes

• All reactions assume standard conditions unless specified.
• Care should be taken with reagent handling and reaction conditions for accurate results.

Reference

• N Goalby, chemrevise.org