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EAS:Halogenation Mechanism definitions

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  • Lewis Acid Catalyst
    Electron pair acceptor that activates diatomic halogen, enabling electrophilic aromatic substitution to proceed.
  • Diatomic Halogen
    Molecule consisting of two identical halogen atoms, such as Br2, used as the halogen source in the reaction.
  • Electrophilic Complex
    Highly reactive species formed by halogen and catalyst, possessing a strong tendency to accept electrons.
  • Benzene
    Aromatic hydrocarbon ring acting as a nucleophile, attacking the activated halogen during substitution.
  • Nucleophile
    Electron-rich species that donates electrons to an electrophile, initiating the substitution process.
  • Arenium Ion
    Carbocation intermediate formed after benzene attacks the electrophile, temporarily disrupting aromaticity.
  • Sigma Complex
    Intermediate structure with a positive charge, stabilized by resonance, formed during aromatic substitution.
  • Resonance Structures
    Multiple valid Lewis structures that depict electron delocalization, stabilizing the reaction intermediate.
  • Elimination Step
    Reaction phase where a proton is removed, restoring aromaticity and completing the substitution.
  • FeBr4−
    Negatively charged iron-bromine complex acting as a nucleophile in the elimination step.
  • Aromaticity
    Special stability of benzene due to delocalized electrons, temporarily lost and then restored during the reaction.
  • HBr
    Byproduct formed when a hydrogen atom is replaced by bromine on the aromatic ring.
  • Catalyst Regeneration
    Process where the Lewis acid catalyst is reformed at the end of the reaction, allowing repeated use.
  • Formal Charge
    Calculated charge on an atom within a molecule, indicating electron gain or loss during complex formation.
  • Substitution
    Replacement of a hydrogen atom on benzene with a halogen atom, characteristic of this reaction mechanism.