Octet / Reactions
Halogenation of Alkene
Halogenation of Alkene (Electrophilic Addition Addition.) Converts CC=CC to CC(Br)C(Br)C using Br₂ (or Cl₂). Stereochemistry: Anti addition (trans-dihalide from cis-alkene).
Reaction details
Halogenation of Alkene
Addition
Electrophilic Addition
CC=CC
CC(Br)C(Br)C
Br₂ (or Cl₂)
CCl₄ or CH₂Cl₂
- Smiles
CC=CC
- Description
2-Butene
- Smiles
CC=CC
- Description
Br₂ approaches, π electrons attack Br
- Smiles
CC1C(C)Br1
- Description
Cyclic bromonium ion forms (prevents rotation)
- Smiles
CC(Br)C(Br)C
- Description
Br⁻ attacks from opposite face (anti addition)
Anti addition (trans-dihalide from cis-alkene)
Bromonium ion intermediate explains anti stereochemistry
In water: halohydrin forms instead
Test for unsaturation: Br₂/CCl₄ decolorizes
Mechanism shown for Br₂; Cl₂ works analogously via chloronium ion
halohydrin-formation
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