1. Chemistry

2. GOC–3

3. Session Objectives

4. Session Objectives
Structural isomerism: chain, positional, functional, ring-chain, isomerism, metamerism , tautomerism Homologous series
Stereoisomerism: conformational, optical and geometrical isomerism

5. Isomerism Isomerism Next slide Structrual Chain Functional Positional
Ring Chain
Metamerism
Tautomerism

6. Isomerism Isomerism Stereoisomerism Previous slide Conformational
Configurational
Optical
Geometrical

7. Structural Isomerism

8. Structural Isomerism Functional Isomerism
Same molecular formulae but differ in the functional groups.
CH3 CH2 OH CH3OCH3
Positional Isomerism
same molecular formulae but differ in the position of the same functional group.

9. Structural Isomerism
Disubstituted benzene has three positional isomers. e.g.

10. Structural Isomerism Metamerism
same molecular formula but the distribution of alkyl groups on either side of the functional group is dissimilar. Occurs in amines, ketones, ethers and esters.

11. Structural Isomerism Ring chain isomerism
Due to the difference in linkage of carbon atoms in the form of ring or open chain structure, i.e. C3H6

12. Structural Isomerism Tautomerism
Existing of single compound in two readily interconvertible structures called as tautomers which appears in acid catalysed or base catalysed conditions.
Tautomerism
keto-enol
nitro-aci
nitrite-nitro

13. Structural Isomerism keto-enol isomerism
Contains a keto and an enol group. For example, in the presence of an acidic or basic catalyst a rapid equilibrium is established between an aldehyde or ketone and its isomeric (tautomeric) forms.

14. Structural Isomerism Shows keto-enol tautomerism
Does not show keto enol tautomerism

15. Structural Isomerism
Nitro-aci tautomerism
nitrite-nitro tautomerism

16. Difference between resonance and keto-enol tautomerism
Shift in the position of electrons only.
Structures are arbitrary and do not exist.
Do not exist in equilibrium.
The functional group does not change.
Lower potential energy stabilize the molecule.
Keto-enol tautomerism
Change in the position of an atom, generally a H–atom.
Exist in solution as they are different compounds.
Exist in dynamic equilibrium.
Possess different functional groups.
Have no stabilization effect on the molecule.

17. Stereoisomerism
Have the same molecular formula and structure but differ in the arrangement of atoms in space.
Tautomerism
Conformational
Geometrical
Optical

18. Stereoisomerism Conformational CH3 H3C H3C CH3 H H
Conformations of Butane (Sawhorse model)

19. Newmann projection
1800

20. Stereoisomerism
Conformations of Cycloalkanes

21. Interconversions
Fischer
Sawhorse
H3C
CO2H OH H H
CO2H OH

22. Interconversions Br H
CH3
CH3 H Br

23. Interconversions H
CHO Br Cl
CH2OH B F
CH2OH Cl
CHO Br H

24. Interconversions H
CO2H OH
CH3

25. Interconversions Ph OH Br
CH3

26. Interconversions H
CO2H OH
CH3

27. Geometrical isomerism

28. Geometrical isomerism
Number of geometrical isomers = 2x x = No. of double bonds
For compounds with two different terminal groups
Example
No. of geometrical isomers =23=8

29. Geometrical isomerism
For two identical terminal groups in alkene
For even no. of double bonds
For odd no. of double bonds
3 geometrical isomers

30. Optical isomerism Criterion for optical activity
Presence of chiral C–atom (for single asymmetric centre)
For more than one asymmetric centres –
Non-superimposable mirror images
Enantiomers (d,l–pair)
Note: Superimposable mirror images
Meso compounds

31. Optical isomerism 2. No plane or centre of symmetry CH3 CO2H OH H H Br
Plane of symmetry (Meso)
No plane of symmetry (Enantiomer)

32. Optical isomerism Centre of symmetry results optical inactivity CH3 HNH C
CH3 H
Centre of symmetry results optical inactivity

33. Optical isomerism When the molecule is asymmetrical:
Number of enantiomers = 2m
Number of meso isomers = 0
2. For symmetrical molecule with even number of asymmetric centres :
Number of enantiomers = 2m–1

34. Optical isomerism
3. For symmetrical molecule and odd number of asymmetric centres

35. Thank you