Important Aromatic Compounds Formulas for JEE and NEET

 Page 2


  
     
  
       
   
    
       
          
          
       
               
          
     
   
  
Step 3 : Loss of a proton gives the products.
       
Br
H
H
H
H
H
bromobenzene
+ HBr + FeBr
3
+
H
intermediate products
reactants
energy
reaction coordinate
Br¯FeBr 4
Br + HBr
+ FeBr
3
T .S
2
-10.8 kcal/mol
+ Br 2
+ FeBr
3
T .S
1
(b) Nitration :
     
?
O H
3
 +  
   
+
  NO
2
(?-complex)
   
H
NO
2
+
(? - complex)
  H
+
   +       
(c) Sulphonation :
The electrophilic reagent, SO
3
, attacks the benzene ring to form the
intermediate carbocation.
2H
2
SO
4
     SO
3
 +  + 
 
Page 3


  
     
  
       
   
    
       
          
          
       
               
          
     
   
  
Step 3 : Loss of a proton gives the products.
       
Br
H
H
H
H
H
bromobenzene
+ HBr + FeBr
3
+
H
intermediate products
reactants
energy
reaction coordinate
Br¯FeBr 4
Br + HBr
+ FeBr
3
T .S
2
-10.8 kcal/mol
+ Br 2
+ FeBr
3
T .S
1
(b) Nitration :
     
?
O H
3
 +  
   
+
  NO
2
(?-complex)
   
H
NO
2
+
(? - complex)
  H
+
   +       
(c) Sulphonation :
The electrophilic reagent, SO
3
, attacks the benzene ring to form the
intermediate carbocation.
2H
2
SO
4
     SO
3
 +  + 
 
  
(d) Friedel Craft reaction :
Alkylation mechanism :
(i)     
(ii)    
(iii)   +  AlCl
4
¯    
Acylation mechanism :
Acylation of benzene may be brought about with acid chlorides or anhydrides
in presence of Lewis acids.
Step 1 : Formation of an acylium ion.
R ? C ? Cl:
||
O
: :
..
..
+  AlCl
3
acylchloride
    R ? C ? Cl ? AlCl
3
||
O
: :
+
- ..
..
complex
  
-
AlCl
4
  +  
[R ? C = O 
..
..
+
R ? C  O:] ?
+
acylium ion
Step 2 : Electrophilic attack.
O
||
C
|
R
+
    
+
O
||
C
R
H
H
sigma complex
Step 3 : Loss of a proton. Complexation of the product.
+
-
O
||
C
R
H
H
sigma complex
:Cl ? AlCl
3
..
..
  
O
||
C
R
acylbenzene
..
..
Page 4


  
     
  
       
   
    
       
          
          
       
               
          
     
   
  
Step 3 : Loss of a proton gives the products.
       
Br
H
H
H
H
H
bromobenzene
+ HBr + FeBr
3
+
H
intermediate products
reactants
energy
reaction coordinate
Br¯FeBr 4
Br + HBr
+ FeBr
3
T .S
2
-10.8 kcal/mol
+ Br 2
+ FeBr
3
T .S
1
(b) Nitration :
     
?
O H
3
 +  
   
+
  NO
2
(?-complex)
   
H
NO
2
+
(? - complex)
  H
+
   +       
(c) Sulphonation :
The electrophilic reagent, SO
3
, attacks the benzene ring to form the
intermediate carbocation.
2H
2
SO
4
     SO
3
 +  + 
 
  
(d) Friedel Craft reaction :
Alkylation mechanism :
(i)     
(ii)    
(iii)   +  AlCl
4
¯    
Acylation mechanism :
Acylation of benzene may be brought about with acid chlorides or anhydrides
in presence of Lewis acids.
Step 1 : Formation of an acylium ion.
R ? C ? Cl:
||
O
: :
..
..
+  AlCl
3
acylchloride
    R ? C ? Cl ? AlCl
3
||
O
: :
+
- ..
..
complex
  
-
AlCl
4
  +  
[R ? C = O 
..
..
+
R ? C  O:] ?
+
acylium ion
Step 2 : Electrophilic attack.
O
||
C
|
R
+
    
+
O
||
C
R
H
H
sigma complex
Step 3 : Loss of a proton. Complexation of the product.
+
-
O
||
C
R
H
H
sigma complex
:Cl ? AlCl
3
..
..
  
O
||
C
R
acylbenzene
..
..
  
e.g.
CH CH
2 3
ethylbenzene
  +  
acetyl chloride
CH ? C ? Cl
3
||
O
     
C
O CH
3
CH CH
2 3
p-ethyl-acetophenone
      (70 ? 80%)
Note : Friedal-Crafts acylations are generally free from rearrangements and
multiple substitution. They do not go on strongly deactivated rings.
e.g.
Chemical Reactions of Benzene :
4 2
3
SO H
HNO . Conc
? ? ? ? ? ? ? ? ?
      + H
2
O
? ? ? ? ? ? ? ? ? ? ?
?
3
4
2
SO SO H . Conc
  + H
2
O
3
2
FeCl
Cl
? ? ? ? ? ?
 + HCl
3
AlCl
RCl
? ? ? ? ? ?
 + HCl     Friedel-Craft?s alkylation
C H
6 6
3
AlCl
RCOCl
? ? ? ? ? ? ?
 + HCl  Friedel-Craft?s acylation
? ? ? ? ? ? ?
?
O D / D
2
 + H
+
 
? ? ? ? ? ?
? ?
2
X ArN
N=N ? Ar
 + HX