1. Chapter 17 Aromatic Substitutions
Organic Chemistry II
Fall 1999
Chapter 17 Aromatic Substitutions
electrophilic aromatic substitutions: E+
mechanism: arenium ion,  672 Figure 17.1
loss of aromaticity: higher DE,  673 Figure 17.2
nitration: nitrobenzene (mixed acid);  673 bot.
formation of a nitronium ion (+NO2):  674 Figure 17.3
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2. Effect of Substituents (I)
Organic Chemistry II
Fall 1999
Effect of Substituents (I)
effect on the reaction rate & regioselectivity
toluene: 17 times faster & ortho/para,  674 bottom
stabilized resonance for ortho/para-substitution
stabilized
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3. Effect of Substituents (II)
Organic Chemistry II
Fall 1999
Effect of Substituents (II)
oxygen (amine): 104 faster;  676
e--donating (resonance) >> e--withdrawing (inductive)
nitrobenzene: 1017 slower & meta;  678 top
practice:  Problem
destabilized
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4. Effect of Substituents (III)
Organic Chemistry II
Fall 1999
Effect of Substituents (III)
chlorine: 17 times slower & ortho/para,  679
e--donating (resonance) < e--withdrawing (inductive)
general substituent effect:  680 Table 17.1
statistics vs steric effect:  681 bottom (~1:4)
toluene (~2:1,  674); anisole (~1:2,  676)
multiple substituents: dominating group,  682
practice:  683 Problem
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5. Nitration: Aniline Derivatives
Organic Chemistry II
Fall 1999
Nitration: Aniline Derivatives
nitrating reagents: HNO3 & H+ 
H+: anhyd. HNO3, H2SO4 (mixed acid), CF3CO2H, CF3SO3H, NO2+BF4-, N2O4 / O3 or O2 (cat.), AcOH
reduction to amine: aniline;  710 top
dinitration: vigorous conditions,  684 middle
nitration of aniline: ammonium ion,  684 bot.
protection to amides: activating, o-/p-,  685 bot.
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6. Halogenation / Sulfonation
Organic Chemistry II
Fall 1999
Halogenation / Sulfonation
less reactive arenes: formation of Cl+ or Br+
Lewis acid catalyst: AlX3 or FeX3,  686 bottom
activated arenes: Cl2 or Br2 (no catalyst)
mesitylene/aniline (disubstitution):  687 bottom
controlled monosubstitution:  688 top
sulfonation: SO3, (H2SO4);  689 top
reversible: heating with H3O+;  689 bottom
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7. Friedel-Crafts Alkylation
Organic Chemistry II
Fall 1999
Friedel-Crafts Alkylation
carbocations (E+): alkyl halides/Lewis acids
mechanism: SN1 type,  Figure 17.4
other carbocations: alcohols/alkenes & acids,  856-7
limitations: multiple alkylation; no reaction with deactivating groups; rearrangement,  692 top
useful intramolecular alkylation: bicylics;  692 middle
synthetic detergents, BHT & BHA:  Focus On
practice:  Problem 17.14, & 17.16
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8. Friedel-Crafts Acylation
Organic Chemistry II
Fall 1999
Friedel-Crafts Acylation
acylium ion (E+): mechanism,  696 bottom
more useful: reaction with weakly deactivated arenes, no rearrangements, no multiple substitution
anhydrides as well as acyl chlorides:  697 top
more para isomer:  697 bottom
intramolecular cyclization: polycyclics;  698 top
electrophilic substitution of polycyclic arenes
more reactive than benzene:  699 bottom
regioselectivity: C-1 (kinetic) vs C-2 (thermodynamic)
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9. Selectivity of Polycyclic Arenes (I)
Organic Chemistry II
Fall 1999
Selectivity of Polycyclic Arenes (I)
substitution at C-1: 7 resonances, more stable
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10. Selectivity of Polycyclic Arenes (II)
Organic Chemistry II
Fall 1999
Selectivity of Polycyclic Arenes (II)
substitution at C-2: 6 resonances, less stable
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11. Nucleophilic Aromatic Substitution
Organic Chemistry II
Fall 1999
Nucleophilic Aromatic Substitution
diazonium ions: mechanism,  700 bottom
substitution of N2: I / F / OH / H; 
Sandmeyer reaction: CuX (X=Cl, Br, CN)
addition-elimination:  704 Figure 17.5
EWG & rate (F > Cl > Br > I):  705 top
elimination-addition:  707 Figure 17.6
benzyne:  706 mid &  Evidences
practice:  Problem
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12. Synthesis of Aromatic Compounds
Organic Chemistry II
Fall 1999
Synthesis of Aromatic Compounds
nitro (NO2)  amine (NH2):  710 top
C=O  CH2: Clemmensen,  710 bot. / Wolff-Kishner,  711 top / catalytic H2,  711 middle
useful for arenes substituted with primary alkyl groups
CHRR’  CO2H:  711 bottom & 712 top
practice:  712 Problem
summary of the reactions:  713 Figure 17.7
practice: m- / p-chloronitrobenzene,  714 top; o-bromophenol,  714 bot.; m-bromochlorobenzene,  715 top; m-bromotoluene,  715 bottom
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