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 Electrophile = + NO 2 (nitronium ion) General Equation:

Sulfonation of Benzene General Equation: Electrophile = + SO 3 H(protonated sulfer trioxide)

Friedel–Crafts Alkylation Electrophile = R  (carbocation) General Equation: EX:

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

Substituents effect on reactivity and orientation EDG (electron-donating group): (R, OH, OR, NR 2,) Reactivity: Ring is electron rich; Ring reacts faster than benzene with E + (Activation) Orientation: Ortho (o), Para (p) position

EWG (electron-withdrawing group): ( CF 3, NO 2, SO 3 H,CN, ) Substituents effect on reactivity and orientation Reactivity: Ring is electron poor; Ring reacts slower than benzene with E + (Deactivation) Orientation: Meta (m) position

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

Reactivity towards electrophilic aromatic substitution

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

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

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

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

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 Exercises Ex5: using benzene or toluene as the only aromatic starting material, devise a synthesis of each compound. a.2-bromo-4-nitrotoluene b.p-nitroethylbenzene