1) The document discusses electrophilic aromatic substitution reactions (EAS), where an electrophile such as a nitronium ion or halogen attacks an aromatic ring.
2) It explains how substituents on the aromatic ring can activate or deactivate the ring towards EAS through electronic effects, directing substitution to the ortho, para, or meta positions.
3) Electron donating groups activate the ring, while electron withdrawing groups deactivate it. Donating groups stabilize ortho/para intermediates, directing to those positions, while withdrawing groups direct to the meta position.
This is Power Point Presentation on Topic "Electrophilic Aromatic Substitution Reactions" as per syllabus of "University of Mumbai" for S.Y. B. Pharmacy (Sem.: IV) students.
This is Power Point Presentation on Topic "Electrophilic Aromatic Substitution Reactions" as per syllabus of "University of Mumbai" for S.Y. B. Pharmacy (Sem.: IV) students.
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I hope You all like it. I hope It is very beneficial for you all. I really thought that you all get enough knowledge from this presentation. This presentation is about materials and their classifications. After you read this presentation you knowledge is not as before.
Retrosynthesis or The Disconnection approach has been discussed in this presentation. Useful Courseware for the Undergraduate and Postgraduate students of Pharmacy , and Chemical Sciences
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Electrophilic aromatic substitution
1. Electrophilic Aromatic SubstitutionElectrophilic Aromatic Substitution
Dr. R B KotnalDr. R B Kotnal
BLDEA’s SSM College of Pharmacy and
Research Centre, Vijayapur
BLDEA’s SSM College of Pharmacy and
Research Centre, Vijayapur
7. Substituent groups on a benzene ring affect electrophilic
aromatic substitution reactions in two ways:
1) reactivity
activate (faster than benzene)
or deactivate (slower than benzene)
2) orientation
ortho- + para- direction
or meta- direction
8. -CH3
activates the benzene ring towards EAS
directs substitution to the ortho- & para- positions
-NO2
deactivates the benzene ring towards EAS
directs substitution to the meta- position
9. Common substituent groups and their effect on EAS:
-NH2, -NHR, -NR2
-OH
-OR
-NHCOCH3
-C6H5
-R
-H
-X
-CHO, -COR
-SO3H
-COOH, -COOR
-CN
-NR3
+
-NO2
increasingreactivity
ortho/para directors
meta directors
11. If there is more than one group on the benzene
ring:
1. The group that is more activating (higher
on “the list”) will direct the next
substitution.
2. You will get little or no substitution
between groups that are meta- to each
other.
13. Orientation and synthesis. Order is important!
synthesis of m-bromonitrobenzene from benzene:
NO2
Br
NO2
HNO3
H2SO4
Br2, Fe
synthesis of p-bromonitrobenzene from benzene:
Br Br Br
NO2
NO2
+
Br2, Fe HNO3
H2SO4
You may assume that you can separate a pure para-
isomer from an ortho-/para- mixture.
14. note: the assumption that you can separate a pure para
isomer from an ortho/para mixture does not apply to any
other mixtures.
Br Br
Br
Br
Br
NO2 NO2
Br
NO2
Br
Br
NO2
Br
Br
Br
Br
NO2
+
+
Br2, Fe Br2, Fe
Br2, Fe Br2, FeHNO3
H2SO4
HNO3
H2SO4
synthesis of 1,4-dibromo-2-nitrobenzene from benzene
separate pure para isomer from ortho/para mixture
cannot assume that these can be separated!
23. 1) R-OH + H+
ROH2
+
3) + R
RDS
4)
H
R
H
R
R
2) ROH2
+ R + H2O
+ H+
Mechanism for Friedel-Crafts with an alcohol & acid
24. 2)
+ R
RDS
3)
H
R
H
R
R
1) C C + H+
R
+ H+
Mechanism for Friedel-Crafts with alkene &
acid:
electrophile in Friedel-Crafts alkylation = carbocation
26. Why do substituent groups on a benzene ring affect the
reactivity and orientation in the way they do?
electronic effects, “pushing” or “pulling” electrons by
the substituent.
Electrons can be donated (“pushed”) or withdrawn
(“pulled”) by atoms or groups of atoms via:
Induction – due to differences in electronegativities
Resonance – delocalization via resonance
27. N
H
H
unshared pair of electrons on the nitrogen
resonance donating groups
(weaker inductive withdrawal)
N
R
R
N
R
H
NR
R
R strong inductive withdrawal
(no unshared pair of electrons on the
nitrogen & no resonance possible
28. H3C C
O
N
H
resonance donation
(weaker inductive withdrawal)
H
O
resonance donation
(weaker inductive withdrawal)
R
O
resonance donation
(weaker inductive withdrawal)
32. Common substituent groups and their effect on reactivity in EAS:
-NH2, -NHR, -NR2
-OH
-OR
-NHCOCH3 electron donating
-C6H5
-R
-H
-X
-CHO, -COR
-SO3H
-COOH, -COOR electron withdrawing
-CN
-NR3
+
-NO2
increasingreactivity
33. Electron donating groups activate the benzene ring to
electrophilic aromatic substitution.
1. electron donating groups increase the electron density
in the ring and make it more reactive with
electrophiles.
2. electron donation stabilizes the intermediate
carbocation, lowers the Eact and increases the rate.
H Y
CH3
34. H Y
NO2
Electron withdrawing groups deactivate the benzene ring to
electrophilic aromatic substitution.
1. electron withdrawing groups decrease the electron density
in the ring and make it less reactive with electrophiles.
2. electron withdrawal destabilizes the intermediate
carbocation, raising the Eact and slowing the rate.
35. CF3
PH2
PO3H
electron withdrawing = deactivating & meta-director
electron withdrawing = deactivating & meta-director
electron donating = activating & ortho-/para-director
36. Br2, Fe
Br + ortho-
NO2
Br2, Fe
NO2Br + ortho-
O
O
Br2, Fe
O
O
Br
+ ortho-
37. How to draw resonance structures for EAS
Y
H
Y
H
Y
H
Y
38. G G G
G G G
G G
H H H
Y Y Y
H
Y
H
Y
H
Y
H Y H Y
G
H Y
ortho-attack
meta-attack
para-attack
39. G
H
Y
G
H Y
If G is an electron donating group, these structures are
especially stable.
40. G G G
G G G
G G
H H H
Y Y Y
H
Y
H
Y
H
Y
H Y H Y
G
H Y
ortho-attack
meta-attack
para-attack
41. Electron donating groups stabilize the intermediate
carbocations for ortho- and para- in EAS more than for
meta-. The Eact’s for ortho-/para- are lower and the
rates are faster.
Electron donating groups direct ortho-/para- in EAS
42. G
H
Y
G
H Y
If G is an electron withdrawing group, these structures
are especially unstable.
43. G G G
G G G
G G
H H H
Y Y Y
H
Y
H
Y
H
Y
H Y H Y
G
H Y
ortho-attack
meta-attack
para-attack
44. Electron withdrawing groups destabilize the intermediate
carbocations for ortho- and para- in EAS more than for
meta-. The Eact’s for ortho-/para- are higher and the
rates are slower.
Electron withdrawing groups direct meta- in EAS
45. Halogens are electron withdrawing but are ortho/para
directing in EAS.
The halogen atom is unusual in that it is highly
electronegative but also has unshared pairs of electrons
that can be resonance donated to the carbocation.
46. X X X
X X X
X X
H H H
Y Y Y
H
Y
H
Y
H
Y
H Y H Y
X
H Y
X
H Y
X
H
Y
ortho-
meta-
para-
halogens are deactivating in EAS but direct ortho and para
47. Common substituent groups and their effect on EAS:
-NH2, -NHR, -NR2
-OH
-OR
-NHCOCH3
-C6H5
-R
-H
-X
-CHO, -COR
-SO3H
-COOH, -COOR
-CN
-NR3
+
-NO2
increasingreactivity
ortho/para directors
meta directors
