B. Sc. Sem - I Unit-IV (D) Orientation by Dr Pramod R Padole

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. Our Inspiration 2

3. 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 (-CH 3 , -OH, -NO 2 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

4. 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 .

5. 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 :

6. 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:

7. 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 .

8. [email protected] 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.

9. 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)

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

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

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

13. Ortho- para directing groups or o-p directors: Directive influence of o, p-directing groups: Example:1) Directive Influence of –OH Group ( Hydroxy Group): But -I effect -of OH group is small as compared to resonance (+R) effect.

14. 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:

15. 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.

16. meta-directing groups or m-directors:

17. meta-directing groups or m-directors:

18. meta-directing groups or m-directors: m-orienting effect of nitro group (-NO 2 ):

19. 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, -CH 3 , -NH 2 Q.2) Predict which of the following groups are o/p directing and m-directing. (S-14, 4 Mark) - Cl , -COOH, -CH 3 , -NO 2 Q.3) Which of the following groups is o/p directing? (W-14 & W-15, ½ Mark) a) -NH 2 b) -NO 2 c) -CHO d) –CN Q.4) Which of the following groups are ortho-para directing and meta-directing. (W-15, 4 Mark) -COOH, -CH 3 , -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) -NH 2 (c) -NO 2 (d) –CHO Q.7) Predict the following groups as o/p directing or m-directing: (S-17, 4 Mark) ( i ) – Cl (ii) -CHO (iii) -CH 3 (iv) –SO 3 H Q.8) –NH 2 group is _______ directing group. (S-18, ½ Mark) Q.9) Classify the following groups into ortho-para directing and meta directing group. ( i ) –OCH 3 ( o/p ) (ii) -C≡N ( m ) (iii) -COOH ( m ) (iv) –CH 2 Cl ( 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) –CH 2 Cl (iv) –SO 3 H (S-19, 4 Mark) Q.11) Which of the following is o/p directing group? (W-19, ½ Mark) (a) –NH 2 (b) –CN (c) –CHO (d) –NO 2

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

21. 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:-

22. 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:

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

24. 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)

25. Activating groups or Ring Activators:

26. Deactivating groups : or Ring De-activators:

27. 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)

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

29. Directive Influence of Halogen, - Cl ( Anomalous behaviour of Halogen): Halogens are ortho-para directing , but ring deactivating groups.

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