Aromatic Compounds

1
Aromatic Compounds
2
Aromatic Systems are Characterized by Their
Chemical Stability

• Note the chemical stability of the aromatic
  systems to the reaction conditions in the
  following slides

3
Note aromatic systems stability toward
hydrogenation
4
Note aromatic systems stability toward strong
reducing agent LiAlH4
5
Note the (two) aromatic systems stability toward
Br2
6
Note the aryl iodides stability toward SN2
substitution (SN2 substitution occurs at the sp3
hybridized carbon)
7
Note the aryl iodides stability toward the
strong base (potassium tert-butoxide) used to
effect elimination
8
Reactions of Aromatic Systems Electrophilic
Aromatic Substitution
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The Friedel-Crafts Reaction
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Treatment of Aryl Halides with Extremely strong
bases (amide anions, NaNH2, pKa of ammonia 38)
can cause substitution reactions
(note that the above table shows the conjugate
acids only)
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But the mechanism involves a two-step process of
elimination-addition.
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Treatment of aryl halides having strongly
electron-withdrawing substituents (at the 2- and
the 4-position) can also cause substitution
reactions But
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The mechanism involves addition-elimination.
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Reactions of Side Chains and Attached
Functionality on Aromatic Compounds
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Treatment of amines with nitrous acid (HONO)
generates diazonium salts
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The Sandmeyer Reaction
Swiss chemist (1854-1922) after whom reaction is
named
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Benzylic Positions Can be Selectively Oxidized
(all the way to the carboxylic acid) by Potassium
Permanganate
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The Clemmensen Reduction
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