1. Structural Isomerism 1
butane
2-methylpropane
C4H10

2. Structural isomerism 2
propan-1-ol
propan-2-ol
C3H8O

3. Structural isomerism 3
butanoic acid
ethyl ethanoate
C4H8O2

4. Geometric isomerism
trans 2-butene
cis 2-butene

5. Optical isomerism
R-2-butanol
S-2-butanol

6. Optical isomerism
An optical isomer (enantiomer) molecule is non-superimposable on its mirror image.
A carbon atom with 4 different groups attached to it gives rise to optical isomerism and is said to be chiral.
A solution of an enantiomer rotates the plane of plane polarised light.
Enantiomers of a molecule have identical m.p. and b.p.
A 1:1 mixture of opposite sense enantiomers is called a racemic mixture and a solution of it has no effect on the plane of plane polarised light.

7. Crystals of tartaric acid (K+ / NH4+ salt)

8. Production of polarised light

9. Perpendicular polarising crystals

10. Importance of optical isomerism
S-thalidomide
(teratogen)
R-thalidomide
(sedative)

11. The Sn2 Mechanism C R1 R3 R2 Cl

12. C R1 R3 R2 Cl O- H

13. Cl
( )- R2 R1 C R3 O H

14. Cl- R1 R2 R3 C O H

15. Cl- R1 R2 R3 C O H

16. Cl- R1 R2 R3 C O H

17. Cl- R1 R2 R3 C O H

18. Cl- R1 R2 R3 C O H

19. Cl- R1 R2 R3 C O H

20. Cl- R1 R2 R3 C O H

21. Cl- R1 R2 R3 C O H

22. Cl- R1 R2 R3 C O H

23. Cl- R1 R2 R3 C O H

24. Cl- R1 R2 R3 C O H

25. Cl- R1 R2 R3 C O H

26. C R1 R3 R2 Cl
Sn2
Reactant R1 R3 R2 O H C
Product
Sn1

27. C R1 R3 R2 Cl
Sn2
Reactant R1 R3 R2 O H C
Product
Sn1

28.                                                                                        
Figure 5 - Action of a sheet of Polaroid on unpolarised light