Aromaticity

Aromaticity思维导图，包括：Tricky defination；Activating/deactivating substituents；Directing substituentis；Acid/Base catalyst on carbonyl reactions。

Aromaticity

• Tricky defination
  • Resonance
    • 1. Failure of lewis structures
      • delocalization of electrons than lewis structure shows
    • 2. Overlapping of atomic p orbitals
  • Conjugation
    • 1. overlapping of bonding π（pi) electrons
      • all conjugations are resonance, and all aromaticities are conjugation
  • hyperconjugation
    • An interaction that results from overlap of a vacant p orbital on one atom with a neighboring C-H σ bond. Hyperconjugation is important in stabilizing carbocations and in stabilizing substituted alkenes
  • aromaticity
    • congjugation has circular, 2(n+1) pi electrons
  • inductive effect
    • withdraw or donation of electrons through a σ bond due to electronegativity
• Activating/deactivating substituents
  • electrong withdrawer
    • inductive electrons withdrawing
      • electronegative atom is directly attached to the ring
        • strong withdrawing: -Cl, -Br, -I, -F
        • weak withdrawing: -OH, NH3
      • also significant when electronegative atom is father removed
        • strong withdrawing: -NO2, -CN, -CHO, -CO2R, -COR, -CO2H
    • resonace electrons withrawing
      • general structure -Y=Z, which Z is more electronegative than Y
        • strong withdrawing: -NO2, -CN, -CHO, -CO2R, -COR, -CO2H
          • meta
  • electron donater
    • inductive electrons donating
      • alkyl substituents
        • hyperconjugation donating effect
          • also stabalize carbocation and substituted alkenes
        • weak donating
          • -CH3
            • ortho, para directing
    • resonance electrons donating
      • with general structure -Y:, which the long pair on Y available to donating
        • so alkyl can't
        • resonance weak donating
          • -halides
        • resonance strong donating
          • -OH, -NH2
  • over all
    • over all deactivating
    • fridel-crafts reaction don't succeed on aromatic rings that are substituted either by a strongly electron withdrawing group or by an amino group
• Directing substituentis
  • Why?
    • depends on cation intermediate's stability
    • meta directing
      • general structure -Y=Z, which Z is more electronegative than Y, it will form repulsive interaction in ortho, para's cation intermediate
        • strong withdrawing: -NO2, -CN, -CHO, -CO2R, -COR, -CO2H
    • ortho, para directing
      • with general structure -Y:, which the long pair on Y available to donating form more (4) resonace forms
        • -OH, -NH2
      • or by alkyl groups form more stable cation intermediate
• Acid/Base catalyst on carbonyl reactions
  • Addition step
    • Acid makes the Carbonyl carbon more electrophylic by protonates carbonyl oxygen
    • Base it self is a better nucleophile: of course if you only want hydrolysis to occur
  • Further leaving group leaving if leaving group contains
    • Acid can protonates leaving group's electronegative atom(like O/N) and make it a better leaving group!
  • So
    • Base only catalyst hydrolysis, and for acyl substitution, its not good enough because can't protonates leaving group
      • some time we use base to neutralize acid formed after acyl substitution。。