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1. Stereoisomerism 2. Chirality 3. Naming stereocenters - R/S configuration 4. Acyclic Molecules with 2 or more stereoc

Chapter 3. Stereochemistry. 1. Stereoisomerism 2. Chirality 3. Naming stereocenters - R/S configuration 4. Acyclic Molecules with 2 or more stereocenters 5. Cyclic Molecules with 2 or more stereocenters 6. Properties of Stereocenters 7. Optical activity

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1. Stereoisomerism 2. Chirality 3. Naming stereocenters - R/S configuration 4. Acyclic Molecules with 2 or more stereoc

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  1. Chapter 3 Stereochemistry 1. Stereoisomerism 2. Chirality 3. Naming stereocenters - R/S configuration 4. Acyclic Molecules with 2 or more stereocenters 5. Cyclic Molecules with 2 or more stereocenters 6. Properties of Stereocenters 7. Optical activity 8. Separation of Enantiomers, Resolution 9. Significance of Chirality in the biological world 20 c a b

  2. configurational isomers diastereomers non-mirror images (cis/trans) enantiomers mirror images non-superposable ISOMERISM same molecular formula, but different…. constitutional connectivity different stereoisomers- same connectivity different 3D orientation conformational isomers chair/boat

  3. cis trans diastereomers

  4. e.g. Prozac - one isomer(“S”)is significantly more active enantiomers

  5. Chirality - right and left-handed substances - 2 spatial arrangements of atoms - analyze reflections (mirrors) same (achiral), different (chiral). plane mirror chiral -non-superposable, different arrangements in space

  6. Elements of Symmetry Plane of symmetry: an imaginary plane passing through an object dividing it such that one half is the mirror image of the other half.

  7. syn - plane of symmetry anti - point of symmetry . Elements of Symmetry Conformations of2,3-butanediol* . If symmetry element is present, substance is achiral *meso or R,S (later)

  8. Elements of Symmetry Center of symmetry: a point situated so identical components of the object are located equidistant on opposite sides.

  9. rotate 180o Chirality superposable mirror images - same compound - a plane of symmetry- achiral

  10. see if images are superposable, e.g. rotate e.g. (180o) Cl C Br F H Chirality-sp3 or tetrahedral center with 4 different groups = chiral molecule Cl Cl C C H H F F Br Br Different, non-superposable mirror images,  enantiomers

  11. Cl Cl C C H H F F Br Br Stereocenter Stereogenic center Tetrahedral - 4 different substituents (sp3) enantiomers - an atom that interchange of 2 groups gives a stereoisomer

  12. R S Enantiomers Lactic acid How do we distinguish chiral molecules? R/S

  13. (7) (8) (35) (17) -Br -NH2 -Cl -OH Increasing priority R,S Convention Priority rules Assign priority to each atom bonded tostereocenter. higher atomic number higher priority (6) (1) -CH3 -H

  14. O > N > C > H 8 > 7 > 6 > 1 R,S Convention 2. If same atoms bonded to the stereocenter, look to next set of atoms. Priority to the first point of difference. “Z” stereocenter, 4 gps.

  15. 3. View C with “4” back; 1, 2, 3 FRONT 3 4 C 1 2 R/S absolute configuration of chiral compounds Rules: 1. Identify stereogenic center (C - 4 different gps.) 2. Assign priority to groups (C - 1, 2, 3, 4) 4. If 1>2>3 clockwise = R; counterclockwise = S R

  16. R S R & S configuration enantiomers

  17. view as R,S Convention 3. Atoms in double (triple) bond viewed as equivalent number of single bonds (C is a stereogenic center)

  18. H H C H C H H C 4 3 H H vs vs 1 2 H^C H C H C C C S C H C H C C H H priorities and assigning R/S

  19. rotate 180o Assign R/S to the stereogenic center of the ester S

  20. R S caraway/dill Assign R/S to stereogenic carbon in coniine R-(-)-coniine poison hemlock Golden pitcher plant Assign R or S to carvone spearmint

  21. Enantiomers & Diastereomers For a molecule with n stereocenters, a maximum of 2nstereoisomers “might” be possible. For a molecule with 1 stereocenter, 21 = 2 stereoisomers are possible. For a molecule with 2 stereocenters, a MAXIMUM of 22= 4 stereoisomers might exist.

  22. 2n 256 (ignore sugar)

  23. what about a second center? R S earlier R|S R - R R - S S - R S - S

  24. R R S S Molecules with more than 1 stereocenter * 22 = 4 trans-1-bromo-2-chlorocyclopropane * relative stereochemistry -both are ‘trans’ absolute stereochemistry - each is unique, enantiomers (1R,2R)-1-bromo-2-chlorocyclopropane (1S,2S)-1-bromo-2-chlorocyclopropane

  25. diastereomers R R S S diastereomers diastereomers enantiomers enantiomers R R S S Molecules with more than 1 stereocenter * 22 = 4 trans-1-bromo-2-chlorocyclopropane * cis-1-bromo-2-chlorocyclopropane (1S,2R)-1-bromo-2-chlorocyclopropane (1R,2S)-1-bromo-2-chlorocyclopropane (1S,2S)-1-bromo-2-chlorocyclopropane (1R,2R)-1-bromo-2-chlorocyclopropane

  26. R R S S R R S S Molecules with more than 1 stereocenter (1S,2R)-1-bromo-2-chlorocyclopropane (1R,2S)-1-bromo-2-chlorocyclopropane (1S,2S)-1-bromo-2-chlorocyclopropane (1R,2R)-1-bromo-2-chlorocyclopropane

  27. R R S S R R S S Molecules with more than 1 stereocenter (1S,2R)-1-bromo-2-chlorocyclopropane (1R,2S)-1-bromo-2-chlorocyclopropane (1S,2S)-1-bromo-2-chlorocyclopropane (1R,2R)-1-bromo-2-chlorocyclopropane

  28. 2 or more stereocenters with symmetry leads to a meso isomer, superposable mirror images. Consider 2,3-dibromobutane: S S R R R S R S

  29. meso isomer is diastereomeric to enantiomers 2 or more stereocenters withsymmetryleads to ameso isomer, superposable mirror images. Consider 2,3-dibromobutane: S R R S meso isomer S R S R only 3 realized part2

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