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Chemical Properties of Halogen Derivatives

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Estimated time: 7 minutes
Maharashtra State Board: Class 12

Key Points: Chemical Properties of Halogen Derivatives

Alkyl halides mainly undergo substitution and elimination reactions.

1. Nucleophilic Substitution Reactions

SN1 (Unimolecular Nucleophilic Substitution):

  • Occurs in two steps:
    • Formation of carbocation
    • Attack by nucleophile
  • First-order reaction (depends only on alkyl halide)
  • Reactivity order:
    Benzylic > 3° > 2° > 1° > methyl
  • Leads to racemisation

SN2 (Bimolecular Nucleophilic Substitution):

  • Occurs in one step (concerted mechanism)
  • Second-order reaction (depends on alkyl halide and nucleophile)
  • Reactivity order:
    Methyl > 1° > 2° > 3°
  • Strong nucleophiles increase the rate
  • Leads to inversion of configuration

2. Reactions of Alkyl Halides

  • With aqueous KOH → Alcohol
  • With alcoholic KOH → Alkene (elimination)
  • With NaOR → Ether
  • With NH₃ → Amine
  • With KCN → Nitrile
  • With AgCN → Isocyanide
  • With KNO₂ → Alkyl nitrite
  • With AgNO₂ → Nitro compound
  • With Mg (dry ether) → Grignard reagent
  • With Na (dry ether) → Alkane (Wurtz reaction)

3. Aryl Halides

  • Undergo electrophilic substitution
    • Nitration
    • Halogenation
    • Sulphonation
    • Friedel–Crafts reactions
  • Show ortho & para directing effect
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