Reactions of Benzene and its Derivatives. Chapter 22. Chapter 22. Reactions of Benzene. The most characteristic reaction of aromatic compounds is substitution at a ring carbon. This is Electrophilic Aromatic Substitution (EAS) . Sulfonation:. H. S. O. 2. 4. S. O. S. O. H. 3. 3.
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Step 1: formation of a chloronium ion.
Step 2: attack of the chloronium ion on the ring.
Step 3: proton transfer regenerates the aromatic character of the ring.
Step 1: attack of the nitronium ion (an electrophile) on the aromatic ring (a nucleophile).
Step 2: proton transfer regenerates the aromatic ring.
enzenesulfonic acidSulfonation of Benzene
Step 1: formation of an alkyl cation as an ion pair.
Step 2: attack of the alkyl cation on the ring.
Step 3: proton transfer regenerates aromaticity.
2. F-C alkylation fails on benzene rings bearing one or more of these strongly electron-withdrawing groups.
Wolff-Kishner reduction, pg 623
Only three resonance structures and
the cation never appears on oxygen.
Four resonance structures here and
the cation does appear on oxygen.
The cation never appears adjacent to the (+) carbon of C=O.
The cation appears adjacent to a (+) carbon of C=O.
Relative rates of reaction for substituted benzenes compared to unsubstituted benzene.
Aniline 106 strongly activating NH2
Toluene 25 weakly activating CH3
Benzene 1 neutral
Chlorobenzene 0.03 weakly deactivating Cl
Nitrobenzene 10-6 strongly deactivating NO2
Benzyne is unstable due to poor orbital overlap,
brackets mean that this is a transient intermediate.
Benzene and its Derivatives
End Chapter 22