Reações de Compostos Aromáticos

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Solutions for Reactions of Aromatic Compounds
OCH(CH3)2
Br
Br
OCH(CH3)2
Br
9
+ Br2
+ Br2
+ HBr (g)
Substitution generates HBr whereas the addition does not. If the reaction is performed in an organic 
solvent, bubbles of HBr can be observed, and HBr gas escaping into moist air will generate a cloud. If the 
reaction is performed in water, adding moist litmus paper to test for acid will differentiate the results of the 
two compounds.
NH2
Ph N
H
C
O
CH3
NH3
C CH3
O
N
H
Ph
10
(a) Nitration is performed with nitric acid and a sulfuric acid catalyst. In strong acid, amines in general, 
including aniline, are protonated.
+ H2SO4 + HSO4
–
(b) The NH2 group is a strongly activating ortho,para-director. In acid, however, it exists as the protonated 
ammonium ion—a strongly deactivating meta-director. The strongly acidic nitrating mixture itself forces 
the reaction to be slower.
(c) The acetyl group removes some of the electron density from the nitrogen, making it much less basic; 
the nitrogen of this amide is not protonated under the reaction conditions. The N retains enough electron 
density to share with the benzene ring, so the NHCOCH3 group is still an activating ortho,para-director, 
though weaker than NH2.
Br
CH
NO2
H H
NO2
HC
Br
H
NO2
CH
Br Br
HC
NO2
H
C
Br
NO2
H
H
NO2
C
H
Br
H
NO2
Br
"extra"
resonance form
ortho
meta
11 Nitronium ion attack at the ortho and para positions places positive charge on the carbon adjacent to 
the bromine, allowing resonance stabilization by an unshared electron pair from the bromine. Meta attack 
does not give a stabilized intermediate.
Substitution:
Addition:
388