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4 Types of Isomers

4 Types of Isomers. Structural Isomers/(Constitutional) Geometric Isomers/( Cis /Trans) Optical Isomers Enantiomers Diastereomers. 4 Types of Isomers. Isomers. Stereoisomer/(Geometric ). Constitutional/(Structural). Same – Formula Diff. – Structure

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4 Types of Isomers

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  1. 4 Types of Isomers

  2. Structural Isomers/(Constitutional) • Geometric Isomers/(Cis/Trans) • Optical Isomers • Enantiomers • Diastereomers

  3. 4 Types of Isomers

  4. Isomers Stereoisomer/(Geometric) Constitutional/(Structural) Same – Formula Diff. – Structure Chemical Properties Physical Properties Biological Properties Enantiomers Diastereomers Same – Formula Structure Chemical Properties Physical Properties Diff. – Geometry Optical Rotation Biological Properties Same – Formula Structure Diff. – Geometry Chemical Properties Physical Properties Biological Properties Geometric/Cis-Trans Same – Formula Structure Diff. – Geometry (C=C) Chemical Properties Physical Properties Biological Properties C4H10 C4H10

  5. Structural Isomers

  6. Different Same • Chemical Formula • Structure • Chemical Properties • Physical Properties • Biological Properties Example C4H10 C4H10

  7. Geometric Isomers

  8. Different Same • Chemical Formula • Structure • Geometry (around C=C) • Chemical Properties • Physical Properties • Biological Properties Example C4H6Cl2 C4H6Cl2 Trans-2,2-dichloro-2-butene Cis-2,2-dichloro-2-butene

  9. Optical Isomers (Enantiomers)

  10. Definition: Chiral molecules that are mirror images of each other. Different Same • Chemical Formula • Structure • Chemical Properties • Physical Properties • Geometry – stereoisomers that are mirror images • Optical Rotation • Biological Properties

  11. Optical Isomers (Diastereomers)

  12. Definition: Chiral molecules that are not enantiomers of each other. Differ in the orientation around one chiral carbon. Different Same • Chemical Formula • Structure • Geometry – stereoisomers that are not enantiomers • Chemical Properties • Physical Properties • Optical Rotation • Biological Properties

  13. Enantiomers vs. Diastereomers

  14. Enantiomers Diastereomers Enantiomers Diastereomers Diastereomers

  15. Plane Polarized Light

  16. Light normally oscillates/vibrates in every direction: Plane Polarized Light oscillates/vibrates in only one direction: Plane Polarized Light can interact with molecules:

  17. Optical Rotation of Plane Polarized Light

  18. Enantiomer A Enantiomer B

  19. Chiral Molecules

  20. Definition: Molecules that lack a plane of symmetry, and therefore have non-superimposable mirror images. Can rotate plane polarized light. Requirements: Carbon atoms with 4 bonds to different groups. No additional plane of symmetry. Important: Chiral molecules that are enantiomers have the same physical and chemical properties but different biological properties.

  21. Achiral Molecules

  22. Molecules that possess chiral carbons but have an additional plane of symmetry • They do not rotate plane polarized light. • Meso compounds are achiral. No Plane of Symmetry Achiral/Meso Chiral

  23. Fischer Projections

  24. Method for drawing chiral molecules in 2D. • Always draw the most oxidized group at the top • The carbon backbone is drawn top-bottom • Swaps are allowed only for horizontal atoms • Odd number of swaps = diff. molecule • Even number of swaps = same molecule 2D Representation of a 3D shape 3D View showing tetrahedral shape

  25. Dextrorotatory and Levorotatory

  26. Dextrorotatory • Rotates light clockwise • (+) • Levorotatory • Rotates light counter clockwise • (-)

  27. Meso Compounds

  28. Definition: Meso compounds have 2 (or more) chiral atoms, but do not rotate plane polarized light due to have an extra plane of symmetry • Extra plane of symmetry • Mirror image = same molecule • Does not rotate plane polarized light Mirror same molecule

  29. Number of Stereoisomer

  30. Maximum number of stereoisomers 2n n = number of chiral carbons • 22 = 4 • 23 = 8 • 24 = 16 • Meso compounds decrease the number of isomers formed

  31. Racemic Mixtures

  32. Definition: A mixture of equal amounts of two enantiomers • Does not rotate plane polarized light (the 2 enantiomers cancel each other out)

  33. Same/Different

  34. Two Fischer projections: • Even # swaps = same molecule • Odd # swaps = different molecule Different One Swap One Swap Same Same

  35. Identifying Chiral Carbons

  36. Definition: Chiral carbons are bonded to 4 different groups of atoms • no C=C or C≡C • watch out for same groups like methyl/ethyl • chiral 4 different groups • H • methyl • ethyl • propyl

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