The document discusses electrophilic aromatic substitution reactions of benzene, including nitration, sulfonation, halogenation, Friedel-Crafts alkylation, and Friedel-Crafts acylation. These reactions involve an electrophilic species attacking the benzene ring. A two-step mechanism is proposed where the electrophile first forms a sigma complex with the benzene ring, generating a positively charged intermediate. This is then followed by a rapid loss of a proton to form the substituted benzene product.

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UNIT I: Benzene and its
derivatives
1. Reactions of benzene - nitration,
sulphonation, halogenation reactivity,
2. Friedel crafts alkylation- reactivity,
limitations,
3. Friedel crafts acylation

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18. https://www2.chemistry.msu.edu/faculty/reusch/virttxtjml/intro1.htm#contnt
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20. Electrophilic Aromatic Substitution
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21. Reaction
Type
Typical Equation
Electrophile
E(+)
Halogenation
:
C6H6
+ Cl2 & heat
FeCl3 catalyst
——>
C6H5Cl + HCl
Chlorobenzene
Cl(+) or Br(+)
Nitration: C6H6
+ HNO3 & heat
H2SO4 catalyst
——>
C6H5NO2 + H2O
Nitrobenzene
NO2
(+)
Sulfonation: C6H6
+ H2SO4 + SO3
& heat
——>
C6H5SO3H + H2O
Benzenesulfonic
acid
SO3H(+)
Alkylation:
Friedel-
Crafts
C6H6
+ R-Cl & heat
AlCl3 catalyst
——>
C6H5-R + HCl
An Arene
R(+)
Acylation:
Friedel-
Crafts
C6H6
+ RCOCl & heat
AlCl3 catalyst
——>
C6H5COR + HCl
An Aryl Ketone
RCO(+)
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23. Two-step mechanism has been proposed for these
electrophilic substitution reactions.
In the first, slow or rate-determining, step the
electrophile forms a sigma-bond to the benzene
ring, generating a positively
charged benzenonium intermediate.
In the second, fast step, a proton is removed from
this intermediate, yielding a substituted benzene
ring.
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26. https://www2.chemistry.msu.edu/faculty/reusch/virttxtjml/benzrx1.
htm
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