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Stereochemistry

Stereochemistry

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Stereochemistry

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  1. Stereochemistry

  2. Stereochemistry: • The study of the three-dimensional structure of molecules • Structural (constitutional) isomers: • same molecular formula but different bonding sequence • Stereoisomers: • same molecular formula, same bonding sequence, different spatial orientation

  3. (S)-ketamine • The properties of many drugs depends on their stereochemistry: (R)-ketamine anesthetic hallucinogen

  4. Optical Isomerism • Optical Activity • The property of the substance to rotate the plane of • the plane-polarized light is known as optical activity. • Dextro-rotatory (+) • Laevorotatory (- ) Necessary condition: Molecule should be dissymmetric. Example: Biphenyl 2, 2’ – disulphonic acid

  5. Enantiomers Enantiomers are defined as the isomers where molecular Structures are mirror images of each other and which rotate the plane of the polarized light equally but in opposite directions. Chirality is the necessary and sufficient condition for the existence of enantiomers. - Properties of enantiomers

  6. Chiral vs. Achiral Example: Identify the following molecules as chiral or achiral.

  7. DiastereomersPair of molecules with two or more different chiral carbon atoms which are neither identical nor non-superimposable mirror images of each other.

  8. Enantiomersnonsuperimposible mirror images

  9. Meso Compound A compound with two or more asymmetric carbon atoms but also having a plane of symmetry (a mirror plane) is called the Meso compound.

  10. Meso CompoundInternal Plane of Symmetry Optically Inactive

  11. Absolute Configuration

  12. Assign Priority to each Group on Asymmetric Center Example priorities: I > Br > Cl > S > F > O > N > 13C > 12C > 3H > 2H > 1H

  13. Lactic Acid

  14. C.I.P. Priorities

  15. (R) and (S) Nomenclature • The two enantiomers of alanine are: Natural alanine Unnatural alanine (S)-alanine (R)-alanine

  16. (R) and (S) Nomenclature 2 4 3 1 CH(CH3)2 > CH2CH2Br > CH3CH2

  17. Fischer Projections

  18. Assigning Absolute Configuration to Fischer Projections

  19. Fischer Projections with 2 Chiral Centers

  20. Tartaric Acids

  21. 2,3,4-trichlorohexaneHow many stereoisomers?

  22. n = 3; 2n = 8

  23. A Carbohydrate

  24. Reactions that Generate Chirality Centers Hydrogenation, syn

  25. BrominationTrans is formed exclusivelyNo Meso is formed (cis)