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

3. 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
6.8 Enantiomeric Resolution 3

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

5. Meso Compounds
Meso compounds: molecules that have 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. A molecule with n stereocenters, can exist as 2n stereoisomers
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?