2. STEREOCHEMISTRY By Puan Azduwin Khasri 8 th November 2012 By Puan Azduwin Khasri 8 th November 2012

3. ISOMERS

4. Isomers -Compound with the same molecular formula but different structures Constitutional Isomer -differ in the way their atoms are connected. Stereoisomer(Configurational isomer)-differ in the way their atom are arranged in space ISOMERS

5. CONSTITUTIONAL ISOMERS Example: C2H6OC2H6O C2H6OC2H6O C 4 H 9 Cl

6. CONFIGURATIONAL ISOMER Cis-Trans Isomers Cis–trans isomers (also called geometric isomers) result from restricted rotation. Restricted rotation can be caused either by a double bond or by a cyclic structure. Cis isomer has the substituent on the same side of the double bond Trans isomer has the substituent on opposite sides of the double bond.

7. Cis-Trans Isomers(Example) Cis- isomer Trans- isomer

8. CONFIGURATIONAL ISOMER An Asymmetric Center Also known as a chirality center. An atom bonded to four different atoms or groups.

9. Chiral vs achiral CHIRAL Nonsuperimposable mirror image. Its mirror image is not the same as itself. ACHIRAL Superimposable mirror image. It looks the same in the mirror

10. Enantiomers GREEN YELLOW BLUE

11. Drawing Enantiomers Perspective formula Solid lines – bonds in the plane of the paper Solid wedge- coming out of the paper toward you Hatched wedge - going back into space behind the paper  The solid wedge and hatched wedge must be adjacent to one another.

12. Horizontal line – The bonds project out of the plane toward the viewer Vertical line- The bonds extend back from the plane away from viewer The carbon chain usually drawn vertically Fischer projection Drawing Enantiomers

13. CLASS EXERCISE 1 Draw enantiomers for each of the following compounds using perspective formulas and Fischer projections;

14. Naming Enantiomers 1.Rank the groups (atoms) bonded to the asymmetric center in order to priority The higher the atomic no. the higher the priority The R,S system of nomenclature

15. 2.Orient the molecules Lowest priority (4) directed away from you. 3.Draw imaginary arrow from the group of highest priority to the next highest priority If the arrow point clockwise (R-Configuration) Counterclockwise (S-Configuration) Naming Enantiomers The R,S system of nomenclature

16. Naming from the Perspective Formula 1. Rank the groups bonded to the asymmetric center with the lowest priority group in the back.

17. 2. If the group (or atom) with the lowest priority bonded by a hatched wedge; Clockwise-R;Anticlockwise-S 3. If the group (or atom) with the lowest priority IS NOT bonded by a hatched wedge; then switch two groups so group 4 is bonded by a hatched wedge

18. 17 Configuration from the Fischer Projection 2. Rank the groups (or atoms) that are bonded to the asymmetric center and then draw an arrow from the highest priority (1) to the next highest priority (2). 1. Consider the 3-dimensional equivalent to the Fischer Projection.

19. 3. If the lowest priority is on a vertical bond; clockwise (R- Configuration),Counterclockwise (S-Configuration) 4. If the lowest priority is on a horizontal bond, the configuration is opposite to the direction of the arrow.

20. ISOMERS WITH MORE THAN ONE ASYMMETRIC CENTER Max no stereoisomer = 2 n n= no. of asymmetric center

21. Diastereoisomers Stereoisomers (1) and (2) Stereoisomers (3) and (4) Stereoisomers (1) and (3),(1) and (4),(2) and (3), (2) and (4) ENANTIOMERS DIASTEREOISOMERS Diastereoisomers are stereoisomers that are not enantiomers

22. 21 Identification of Asymmetric Carbons in Cyclic Compounds Identification of Asymmetric Carbons in Cyclic Compounds

23. 22 Meso Compounds Have two or more asymmetric centers and an internal plane of symmetry (  -plane) Meso compounds are achiral molecules with asymmetric centers

24. 23 If a compound with two asymmetric centers has the same four groups bonded to each of the centers, one of its stereoisomers will be a meso compound

25. THE END THANK YOU