Asymmetric synthesis
Name : Harchand Tudu
Roll No : 2173022
Branch : PG – II Dept. of Chemistry
CONTENTS
DEFINITION
 ENANTIOMERIC EXCESS ( ee )
 STEREOSELECTIVE &
STEREOSPECIFIC REACTION
 KINETIC RESOLUTION OF
RACEMATES

 DEFINITION
Asymmetric synthesis or chiral synthesis is a reaction in
which an achiral unit in the substrate molecule is converted
into a chiral unit in such a manner that unequal amount of
chiral stereoisomer either enantiomeric excess (ee) or
diastereomeric excess (de).
 When a compound containing an asymmetric carbon is
synthesized by conversional laboratory method form an
achiral compound the product will be a racemic mixture.
 In such a synthesis is carried out under chiral influence , only
one of optically active isomer will form preferentially over
another.

For example the reduction of pyruvic acid ,
CH3
I
C=O
I
COOH
 ENANTIOMERIC EXCESS

Enantiomeric excess replace the percentage to which a
sample contains one enantiomer in greater amount than
other.

A racemic mixture or dl-mixture has an enantiomeric
excess of zero percentage.

A single completely pure enantiomer has an enantiomeric
excess of 100%.

For example, consider a sample with 70% of R-isomer( Dform ) and 30% of S-isomer( L-form ).We have enantiomeric
excess of 40%.
 This can also be thought of a mixture of 40% pure ‘R’ with 60%
of racemic mixture ( 30% of R- form and 30% of S-form ).