1 (390)

Prévia do material em texto

SOLUTIONS FOR REACTIONS OF AROMATIC COMPOUNDS
From Chapter 17 of Solutions Manual for Organic Chemistry, Eighth Edition. Leroy G. Wade, Jr., Jan W. Simek. Copyright © 2013 by Pearson Education, 
Inc. All rights reserved.
HCl +
+ AlCl3
++
+
1
Cl Cl Al
Cl
Cl
Cl
H
H
H
H
H
H
Cl Cl Al
Cl
Cl
Cl
H
H
C
H
H
H
H
Cl Al
Cl
Cl
Cl
H
H
Cl
H
H
H
Cl
Cl
C
H
H
H
H
H
HH
H
H
H
H
C
H
Cl
Cl Cl Al
Cl
Cl
Cl
The representation of benzene with a circle to represent the π system is fine for questions of nomenclature, 
properties, isomers, and reactions. For questions of mechanism or reactivity, however, the representation 
with three alternating double bonds (the Kekulé picture) is more informative. For clarity and consistency, 
this Solutions Manual will use the Kekulé form exclusively.
Cl Al
Cl
Cl
Cl
Cl
2
C
H
I
H
sigma
complex
OH2 C
H
I
H O
H
H
OH2 C
H
I
H OH
addition product—
NOT AROMATIC
Though the addition of water to the sigma complex can be shown in a reasonable mechanism, the 
product is not aromatic. Thus, it has lost the 151 kJ/mol (36 kcal/mole) of resonance stabilization 
energy. The addition reaction is not favorable energetically, and substitution prevails.
CH3
CH3
CH
NO2
H
CH3
CH3
H
NO2
HC
CH3
CH3
C NO2
H
CH3
CH3
2° 3°2°
Benzene's sigma complex has positive charge on three 2° carbons. The sigma complex above shows 
positive charge in one resonance form on a 3° carbon, lending greater stabilization to this sigma 
complex. The more stable the intermediate, the lower the activation energy required to reach it, and the 
faster the reaction will be.
3
+ N
O
O
385