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Electrophilic Aromatic Substitution (EAS)Reactions

Electrophilic Aromatic Substitution (EAS)Reactions. Overall reaction. General Mechanism for Electrophilic Aromatic Substitution. Summary of ERS Reactions. Halogenation of Benzene. General Equation:. Electrophile = X +. EX:. Nitration of Benzene. General Equation:.

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Electrophilic Aromatic Substitution (EAS)Reactions

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  1. Electrophilic Aromatic Substitution (EAS)Reactions Overall reaction

  2. General Mechanism for Electrophilic Aromatic Substitution

  3. Summary of ERS Reactions

  4. Halogenation of Benzene General Equation: Electrophile = X+

  5. EX:

  6. Nitration of Benzene General Equation: Electrophile = +NO2 (nitronium ion)

  7. Sulfonation of Benzene General Equation: Electrophile = +SO3H(protonatedsulfer trioxide)

  8. Friedel–Crafts Alkylation General Equation: Electrophile = R+(carbocation) EX:

  9. Friedel–Crafts Acylation Acyl group: General Equation: Electrophile is R–C≡O⊕ (acylium ion)

  10. Substituents effect on reactivity and orientation EDG (electron-donating group): (R, OH, OR, NR2,) Reactivity: Ring is electron rich; Ring reacts faster than benzene with E+ (Activation) Orientation: Ortho (o), Para (p) position

  11. Substituents effect on reactivity and orientation EWG (electron-withdrawing group): (CF3 , NO2, SO3H,CN, ) Reactivity: Ring is electron poor; Ring reacts slower than benzene with E+ (Deactivation) Orientation: Meta (m) position

  12. Substituents effect on reactivity and orientation Halogens (X): (F, Cl, Br, I) Reactivity: Ring reacts slower than benzene with E+ (Deactivation) Orientation: Ortho (o), Para (p) position

  13. Reactivity towards electrophilic aromatic substitution

  14. arenium ion stabilized Effect of Electron-Donating (releasing) and Electron-Withdrawing Groups If G is electron-donating group then reaction is faster than with benzene

  15. arenium ion destabilized If G is an electron-withdrawing then reaction is slower than with benzene

  16. EDG activate the ring by: (1) Mesomeric (+M) Effects: Activate the ring by resonance (2) ) Inductive (+I): Activate the inductive (through σ bond) Note: Mesomeric effect stronger than Inductive effect

  17. EWG deactivate the ring by: (1) Mesomeric (-M) Effects: Deactivate the ring by resonance effect (2) ) Inductive (-I): Deactivate the ring by negative inductive effect Note: Mesomeric effect stronger than Inductive effect

  18. Exercises Ex1: Write the formulas for benzyl chloride, toluene, and benzoic acid, ortho-xylene, 4-ethyl-2,6-difluorotoluene, Ex2: Draw the important resonance contributors for the benzenonium intermediate in the bromination of aniline Ex3: Devise a synthesis for each of the following, starting with benzene: a. m-bromobenzenesulfonic acid b. p-nitrotoluene Ex4: Which compound is more reactive toward electrophilic substitution • Ex5: using benzene or toluene as the only aromatic starting material, devise a synthesis of each compound. • 2-bromo-4-nitrotoluene • p-nitroethylbenzene

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