1. Electrophilic
Substitution Reactions
Mrs. Vastvikta Sahai

2. Definition:
 Substitution reaction
Functional group attached to a compound
Replaced by an electrophile.
The displaced functional group is often a H atom.

3. Types of Electrophilic Substitution Reaction
Electrophilic
Aromatic
Substitution
Reaction
Atom attached to an
aromatic ring is
replaced
Examples: aromatic
nitrations, aromatic
sulphonation etc
Electrophilic
Aliphatic
Substitution
Reaction
Generally hydrogen in
an aliphatic compound
is replaced
Examples: Insertion of
a carbene into a
carbon-hydrogen bond
•Diazonium coupling
(aliphatic)

4.  Example of Electrophilic Aromatic
Substitution Reaction
Example of Electrophilic Aliphatic
Substitution Reaction

5. Mechanism:
1. Generating Electrophile
oRequirement- Anhydrous
AlCl3 (Lewis Acid).
AlCl3 aids in generating
electrophile from alkylation,
halogenation, acylation of
an aromatic ring.
Electrophiles formed are:
X+, R+, RC+O
2.Forming Carbocation
Electrophile will attack at
the aromatic ring  arenium
ion/ sigma complex. 1
carbon in arenuim ion is sp3
hybridised.
Delocalization of electrons
stops at the sp3 hybridized
carbon  arenium ion will
lose its aromaticity
3. Eliminating Proton
To restore the aromaticity,
the sigma complex will
release a proton from the
sp3 hybridized carbon when
it is attacked by the [AlCl4]–.

6. Reactions for Mechanism:
1. Generating Electrophile
Chlorinium Ion

7. 2.Forming Carbocation

8. 3. Eliminating Proton

9. Thank you!!
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