Organic Chemistry: Addition Reactions

Introduction to Addition Reactions

• Definition: Addition reactions involve adding atoms to a molecule, typically transforming double bonds to single bonds.
• Basic Concept: Start with an unsaturated compound (double bonds) and add elements to form saturated compounds (single bonds).

Example

• But-1-ene: An alkene with a double bond.
• Addition of Hydrogen (H₂): Hydrogenation breaks the double bond, converting it to a single bond, resulting in an alkane.
• Product Formation: Addition provides space for each carbon to have four bonds, allowing hydrogen intake.

Types of Addition Reactions

1. Hydrogenation

   • Adds H₂ (hydrogen) to alkenes.
   • Example: Transforming but-1-in to butane.
   • Catalyst: Often platinum, indicating hydrogenation.

2. Halogenation

   • Adds diatomic halogens (e.g., Cl₂, Br₂).
   • Example: Chlorine (Cl₂) added to hex-1-ene resulting in 1,2-dichlorohexane.
   • Reaction Condition: Occurs easily at room temperature without heat or water.

3. Hydrohalogenation

   • Adds hydrogen and a halogen (e.g., HCl, HBr).
   • Makovnikov's Rule: Hydrogen is added to the carbon with more hydrogens; forms major product.
   • Example: But-1-ene reacting with HBr.
   • Product: Formation of a haloalkane.

4. Hydration

   • Addition of H₂O to alkenes forming alcohols.
   • Reaction Conditions: Requires a strong acid catalyst (sulfuric/phosphoric acid) and water in excess.
   • Makovnikov's Rule: Again applied for major product formation.
   • Example: But-1-ene with water forming butan-2-ol.

Reaction Conditions

• Hydrogenation: Requires a platinum catalyst.
• Halogenation: Room temperature.
• Hydrohalogenation: No water; follow Makovnikov’s rule.
• Hydration: Strong acid catalyst and excess water.

Summary

• Addition reactions convert unsaturated compounds (double bonds) into saturated compounds (single bonds).
• Types include hydrogenation, halogenation, hydrohalogenation, and hydration with specific conditions and rules (e.g., Makovnikov's rule) guiding the major and minor product formation.