Orientation: Effect of substituent groups. Activating and deactivating groups. Theory of reactivity and orientation on the basis of inductive and resonance effects (-CH3, -OH, -NO2 and –Cl groups).

1. 1
B.Sc. First year
Students
Semester – I
Unit-IV
(D) Orientation
by
Dr Pramod R Padole

2. 2

4. Unit IV- Aromatic Hydrocarbons
Orientation: Effect of substituent groups. Activating and
deactivating groups.
Theory of reactivity and orientation on the basis of inductive
and resonance effects (-CH3, -OH, -NO2 and –Cl groups).
D
Nomenclature and Isomerism of Aromatic Compounds:
Structure of Benzene: Kekule structure and Molecular orbital structure.
A
Aromaticity and Huckel’s rule Aromatic, antiaromatic and
non-aromatic systems
B
Mechanism of Electrophilic Aromatic Substitution: Nitration,
Friedal Craft Alkylation and Acylation.Nuclear and Side Chain
Halogination, Birch Reduction
C

5. LOGO
D) Orientation:
The process of determine the position of substituent in the
substituted benzene is called orientation.
Or The relative arrangement of atoms or groups on the
aromatic ring is called orientation.

6. By Dr Pramod R Padole
Orientation:
Defination: The process of determine the position of substituent in
the substituted benzene is called orientation.
Or
Defination: The relative arrangement of atoms or groups on the
aromatic ring is called orientation.
 The new group is located either ortho, meta or para positions to the
existing substituent (first/original).
 The identity of the first substituent determines the position of the
second substituent.
 Substitution in Mono-substituted Benzene:

7. By Dr Pramod R Padole
Effect of Substituent groups on further
Electrophilic Substitution:
Directing
(or orienting)
influence
Effect
Of
Substituent
Activity effect
(or influence)
There are two types of influence of substituent's:

8. Directing (or orienting) influence:
Substituent group, X, directs the incoming
group, Y, either to ortho and para positions
or only to m-position.
 This effect of group already present (-X)
on the benzene ring is known as orienting
(directive) influence of the group or
orientation effect.

9. pramodpadole@gmail.com
By Dr Pramod R Padole
Directing (or orienting) influence:
Ortho-Para
(o/p) Directing
Groups:
or
o-p directors:
Directing
(Orienting)
influence
meta
(m)
Directing Groups:
or
m directors:
The substituent groups are thus classified into two types.

10. Ortho-para directing groups or o-p directors:
Ortho-para directing groups or o-p directors:
The group (first substituent) which directs the second
incoming group (i.e. second substituent) to the ortho-para
(o-p) positions of the aromatic ring or benzene ring
simultaneously are called ortho-para directing groups or
o-p directors.
Q.1) Explain: Ortho-Para directing groups with a suitable example. (S-04, W-05 & S-06, 2 Mark)
Q.2) Define with a suitable example: Ortho-Para directing groups. (S-12 & W-13, 2 Mark)

11. Ortho-para directing groups or o-p directors:

12. Ortho-para directing groups or o-p directors:

14. Ortho-para directing groups or o-p directors:
CH3
Toluene
+ I effect

15. Ortho-para directing groups or o-p directors:
Directive influence of o, p-directing groups:
 Example:1) Directive Influence of –OH Group (Hydroxy Group):
OH
I II III
Phenol
Resonance structures of Phenol
Three R.S. place a -ve charge on C-atoms in the ring



:
:
OH
:
OH
:
OH
:
OH
:

Resonance hybrid
OH
Phenol
:
:
- I effect
But -I effect -of OH group is small as compared to
resonance (+R) effect.

16. LOGO
meta Directing Groups:
Q.1) Explain: Meta directing groups with a suitable example.
(S-04, W-05 &S-06, 1-2 Mark)
Q.2) Define m- directing groups with examples.
(S-11& W-13, 2 Mark)
Q.3) What is meta directing groups? (W-16, 2 Mark)
m- directors:
•meta Directing Groups:

17. meta-directing groups
or m-directors:
 The group (first substituent) which directs the
second incoming group (i.e. second substituent) to
the meta (m-) position of the aromatic ring or
benzene ring are called meta- directing groups or
m-directors.

18. meta-directing groups
or m-directors:

19. meta-directing groups
or m-directors:

21. meta-directing groups
or m-directors:
m-orienting effect of nitro group (-NO2):
Nitrobenzene
strong - I effect & - R effect
- R effect NO2
- I effect
N
I II III
Nitrobenzene
Resonance structures of nitrobenzene


 
Resonance hybrid
O
O
N
O
O
N
O
O
N
O
O
N
O
O
Nitrobenzene


 
Resonance hybrid
N
O
O
+ E
electrophile
NO2
E
meta-substituted product
of nitrobenzene

23. By Dr Pramod R Padole
Problems:
Q.1) Which of the following groups are ortho-para directing and meta-directing. (S-13, 2 Mark)
-COOH, -OH, -CH3, -NH2
Q.2) Predict which of the following groups are o/p directing and m-directing. (S-14, 4 Mark)
-Cl, -COOH, -CH3, -NO2
Q.3) Which of the following groups is o/p directing? (W-14 & W-15, ½ Mark)
a) -NH2b) -NO2 c) -CHO d) –CN
Q.4) Which of the following groups are ortho-para directing and meta-directing. (W-15, 4 Mark)
-COOH, -CH3, -CHO, -OH
Q.5) Nitro group is _______ directing group. (S-16, ½ Mark)
Q.6) Which of the following group is o-p directing group: (W-16, ½ Mark)
(a) -COOH (b) -NH2 (c) -NO2 (d) –CHO
Q.7) Predict the following groups as o/p directing or m-directing: (S-17, 4 Mark)
(i) –Cl (ii) -CHO (iii) -CH3 (iv) –SO3H
Q.8) –NH2 group is _______ directing group. (S-18, ½ Mark)
Q.9) Classify the following groups into ortho-para directing and meta directing group.
(i) –OCH3 (o/p) (ii) -C≡N (m) (iii) -COOH (m) (iv) –CH2Cl (o/p) (S-18, 4 Mark)
Q.10) Classify the following groups into ortho-para directing and meta directing group.
(i) –OH (ii) –COCl (iii) –CH2Cl (iv) –SO3H (S-19, 4 Mark)
Q.11) Which of the following is o/p directing group? (W-19, ½ Mark)
(a) –NH2 (b) –CN (c) –CHO (d) –NO2

25. Activity effect ( or influence):
On the basis of activation & deactivation of the aromatic ring or nucleus by the substituent.

26. On the basis of activation & deactivation of the aromatic ring or nucleus by the substituent.
Activity effect (or influence):
Activating
groups
Or
Ring
Activators:
Activity Effect
or
Influence:
Deactivating
groups
Or
Ring
De-activators:
Substituents are divided into two types:-

28. By Dr Pramod R Padole
Effect of Substituent groups on further
Electrophilic Substitution:
Directing
(or orienting)
influence
Effect
Of
Substituent
Activity effect
(or influence)
There are two types of influence of substituent's:

38. LOGO
By Dr Pramod R Padole
Activating Groups:
or
Ring Activators:

39. LOGO
Activating groups or Ring Activators:
 Activating groups or Ring Activators:
 The groups or substituent( first) which increases the rate of second
substitution (reactivity of benzene for further electrophilic substitution) are
called as activating groups or Ring Activators.
 All ortho-para directing groups, except halogens are ring activating groups or
Ring Activators.
The o/p directing groups, except halogens, donate the electrons to benzene ring.
These groups increase the electron density of benzene ring, which makes
the benzene ring more reactive than benzene towards further
electrophilic substitution reaction.
Such groups are called ring activating groups.
Q.1) Explain: Ring Activating Groups with a suitable example (W-04, S-06, W-07, S-08, S-09 & S-16, 2 Mark)
Q.2) What are ring activating groups? Explain with suitable examples. (W-07, W-10 & S-19, 2 Mark)
Q.3) Define: Activating groups with examples. (S-11, S-14 & W-16, 2 Mark)
Q.4) Define with suitable example of Activating group. (W-18 & W-19, 2 Mark)
Examples: O , NH2, NHR, OH, OR, CH3, CH2OH, CH2Cl , C6H5, etc.
..
..
.. .. ..
..
..
..
..
..
..
..:

40. LOGO
Activating groups or Ring Activators:

41. LOGO
Deactivating groups :
or Ring De-activators:

42. Deactivating groups or Ring De-activators:
Deactivating groups or Ring De-activators:
 The groups or substituent (first) which decreases the rate of second
substitution (decreases the reactivity of benzene for further
electrophilic substitution) are called as de-activating groups or
Ring de-activators.
 The meta directing groups along with halogens (it is o/p-directing group)
withdraws electrons from the benzene ring. This decreases the electron
density of the benzene ring, which makes the benzene ring less reactive
than benzene itself, towards further electrophilic substitution reaction.
Hence, these groups are called as ring deactivating groups.
 All meta-directing groups along with halogens are ring deactivating
groups.
 Halogens are o-p directing groups but ring deactivating groups.
Q.1) Explain:- Deactivating Groups with a suitable example. (W-04, S-06, W-07, S-08 & S-09, 1-2 Mark)
Q.2) What are ring deactivating groups? Explain with suitable examples. (W-07, W-10& S-19, 2 Mark)
Q.3) Define with a suitable example: Deactivating Groups. (S-12, S-14, W-16, W-18 & W-19, 2 Mark)
Q.4) Write the structural formula of Benzene sulphonic acid. (S-18, 1 Mark)

43. Deactivating groups or Ring De-activators:
All meta-directing groups along with halogens are ring deactivating groups.

45. LOGO

46. LOGO
Directive Influence of Halogen, -Cl
( Anomalous behaviour of Halogen):
 Halogens are ortho-para directing, but ring
deactivating groups.
Chlorobenzene
:
Cl
:
:
- I effect is more stronger than + R effect
+ R effect
Cl
I II III
Chlorobenzene
Resonance structures of Chlorobenzene



:
:
Cl:
:
Cl:
:
Cl:
:
Cl:
:

Resonance hybrid
:

47. LOGO

48. LOGO

49. LOGO
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(D) Orientation by Dr Pramod R. Padole
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