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STEREOCHEMISTRY

STEREOCHEMISTRY. By Puan Azduwin Khasri 8 th November 2012. ISOMERS. ISOMERS. Isomers -Compound with the same molecular formula but different structures Constitutional Isomer -differ in the way their atoms are connected.

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STEREOCHEMISTRY

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  1. STEREOCHEMISTRY By PuanAzduwinKhasri 8th November 2012

  2. ISOMERS

  3. ISOMERS • 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

  4. CONSTITUTIONAL ISOMERS Example: C2H6O C4H9Cl

  5. CONFIGURATIONAL ISOMERCis-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. • Cisisomer has the substituent on the same side of the double bond • Trans isomer has the substituent on opposite sides of the double bond.

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

  7. CONFIGURATIONAL ISOMERAn Asymmetric Center • Also known as a chirality center. • An atom bonded to four different atoms or groups.

  8. Chiralvsachiral CHIRAL • Nonsuperimposablemirror image. • Its mirror image is not the same as itself. ACHIRAL • Superimposablemirror image. • It looks the same in the mirror

  9. Enantiomers YELLOW GREEN BLUE

  10. 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.

  11. Drawing Enantiomers • Fischer projection • 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

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

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

  14. Naming Enantiomers The R,S system of nomenclature 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)

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

  16. 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

  17. Configuration from the Fischer Projection 1. Consider the 3-dimensional equivalent to 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).

  18. 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.

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

  20. 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

  21. Identification of Asymmetric Carbons in Cyclic Compounds

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

  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

  24. THE END THANK YOU

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