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Resolution of Enantiomers Part II

Resolution of Enantiomers Part II. Diastereomeric Salt Formation Separation of enantiomers from a racemic mixture Enantiomers are temporarily converted into a mixture of diastereomers Diastereomers have different physical properties Do this by combining enantiomers with a resolving agent

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Resolution of Enantiomers Part II

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  1. Resolution of Enantiomers Part II • Diastereomeric Salt Formation • Separation of enantiomers from a racemic mixture • Enantiomers are temporarily converted into a mixture of diastereomers • Diastereomers have different physical properties • Do this by combining enantiomers with a resolving agent • Resolving agent • Chiral compound • Enantiomerically pure

  2. By this method a racemic mixture of an amine may be resolved with a chiral carboxylic acid Resolving Agent Racemic Mixture

  3. 6.8 Enantiomeric Resolution Two diastereomeric salts are formed These salts have different physical properties The (S,R,R)-diastereomer is less soluble in methanol and can be selectively crystallized 3

  4. 6.8 Enantiomeric Resolution Each pure enantiomer may then be recovered by decomposition of the salt with base 4

  5. Meso Compounds • Meso compounds: molecules thathave two or more chiral carbons yet are achiral • not optically active • Possess an internal mirror plane Stereoisomers of 2,3-Butanediol

  6. Stereoisomers of 2,3-Butanediol • An internal plane of symmetry is present 6.7 Meso Compounds

  7. Stereoisomers of 2,3-Butanediol • Two of the stereoisomers are the same • Hence, there are only three stereoisomers of 2,3-butanediol 6.7 Meso Compounds

  8. Stereoisomers of 2,3-Butanediol • Relationship among the 2,3-butanediol stereoisomers 6.7 Meso Compounds

  9. Meso Compounds • A molecule with n stereocenters, can exist as 2n stereoisomers • This number is reduced if a meso compound is present among the possibilities • 2,3-Butanediol possesses two stereocenters = 2n = 22 = 4 possible stereoisomers 6.7 Meso Compounds

  10. Problems • Which of the following structures represent meso compounds?

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