Stereochemistry of organic compounds involves the optical isomerism, racemization, resolution, and asymmetric synthesis of compounds. A racemic mixture contains equal amounts of left- and right-handed enantiomers, making it optically inactive due to cancellation. Resolution methods separate enantiomers, including preferential crystallization, biochemical separation using microorganisms, chemical reactions forming diastereomers, precipitation, and chromatographic separation. Asymmetric synthesis produces an optically active compound from an inactive one using a chiral reagent or catalyst.

1. Stereochemistry of
organic compounds
Optical isomerism: racemization, resolution and
asymmetric synthesis

2. Racemic mixture
• Mixture containing equal amounts of enantiomers
• Optically inactive
• The optical rotation of one isomer will be cancelled
out by another
• External compensation
Racemization
Process of converting the (+) or (-) form of a
compound into a racemic mixture

3. Resolution
• Process of separation of a racemic mixture to its
enantiomers
• Methods:
• Mechanical separation
• Preferential crystallization
• Biochemical Separation
• Chemical Method
• Precipitation
• Chromatographic separation
• Kinetic method

4. 1. Mechanical separation
• This invoved mechanical separation of the crystal of
one enantiomers from the other in racemic mixture
based on difference in their shapes
• Crystal of the two forms have different shapes
separated by magnifying lens and forceps
• This method first used by pasteur for he resolutiuon of
sodium ammonium tartarate which crystallise out in
the form of racemic mixture below 27 degree
• This methods is time consuming and every compound
can not be crystallized at room temperature

5. 2. Preferential crystallization
• This method involve seeding of a saturated solution
of the racemic mixture with a pure crystal of one
the two enantiomers.
• The solution now become super saturated with
respect to the added enantiomers
• It begins to crystallize out
• Eg. Harda obtained free from amino acid by adding
corresponding d/l isomers of amino acid

6. 3. Biochemical Separation
• It was introduced by Pasteur in 1858.
• This method is based on fact that when certain
micro organisms like bacteria, fungi, yeast, moulds,
etc. are grown in dilute solution of racemic mixture,
they eat up one enantiomer rapidly than other.
• Example: the mould penicillium glaucum
preferentially destroys the (+) isomer of racemic
ammonium tartarate leaving (-) ammonium
tartarate in solution.

7. 4. Chemical Method
• When racemic mixture is allowed to react with
optically active material, it give a diastereomeric
derivatives.
• Diastereomer have different physical properties
and hence can easily separated into two
component by fractional crystallization

9. 5. Precipitation
• This method is based on formation of precipitate by
reaction between any reagent and racemic mixture.
• Example: (+) & (-) narcotine when dissolved in HCl ,
precipitates (+) narcotine.

10. 6. Chromatographic separation
• The racemic mixture can be separated by
chromatography on an optically active support.
• The diastereomeric adsorbates which are formed
have different stabilities.
• Thus one enantiomer will be held more tightly than
the other and would be eluted first.

11. 7. Kinetic method
• This method is based on the fact that one of the
enantiomer of racemic mixture reacts faster than
other with optically active compound.
• menthol reacts faster with (+) mandelic acid than
with (-) mandelic acid.
• Thus with difference in kinetics of reaction, racemic
mixture can be separated

12. Asymmetric synthesis
• The synthesis of an optically active compound from
an optically inactive compound in the presence of a
sutable chiral reagent or catalyst