This document discusses stereochemistry and stereoisomers. It defines stereoisomers as isomers that have the same molecular formula and connectivity but differ in the three-dimensional arrangement of atoms. There are two main types of stereoisomers - enantiomers, which are nonsuperimposable mirror images of each other, and diastereomers, which are not mirror images. Chirality and how compounds interact with polarized light are also explained. The Cahn-Ingold-Prelog system for assigning R and S configurations to chiral centers is described. Examples are provided to illustrate key stereochemistry concepts.

1. STEREOCHEMISTRY

2. W h a t is
S t e r e o is o m e r ?

3. Identical (Same Compounds) Stereoisomers (Different
Compounds)

4.  Isomers:
Different compounds with same molecular
formula
 Stereoisomers:
isomers that have same molecular formula and
connectivity but differ in the way the atoms are
oriented in space - i.e. the difference between
two stereoisomers lies only in the three
dimensional arrangement of atoms.
 Stereochemistry:
chemistry that studies the properties of stereo-
isomers

6.  Two types of stereoisomers:
◦ enantiomers
 two compounds that are nonsuperimposable
mirror images of each other
◦ diastereomers
 Two stereoisomers that are not mirror
images of each other
 Geometric isomers (cis-trans isomers) are one
type of diastereomers.

9.  The Light whose electric fields oscillate in
single plane.

12.  The ability of a compound to rotate the plane
polarized light either clockwise or anti-
clockwise. E.g. Tartaric Acid

13. Substances should be light sensitivity.
They should have chiral carbon
They should rotate plane polarized light
(PPL) in different ways.
As a result, they should produce two
different configurations i.e. enantiomers

14.  An optically active compound that rotates
plane polarized light in a clockwise direction
e.g. (+)Epinephrine

15. An optically active compound that rotates
plane polarized light in anti-clockwise
direction. E.g. (-) Epinephrine

16. A carbon which is bonded with four different
groups.

17.  Some molecules are chiral:
Asymmetric
(chiral) carbon

18.  Organic compounds that contain a chiral
Carbon usually have two non
superimposable structures. These two
structures are mirror images of each other.

19.  Have identical molecular formula
 Have same physical properties
 Both rotate plane polarized light (PPL) but in
opposite sense.
 One rotates PPL to clockwise and another to
anti-clockwise.

20.  Equimolar mixture of left- and right-handed
enantiomers of a chiral molecule.
Properties
 Optically inactive i.e. zero (0) rotation
 Sometimes have different properties of either
pure enantiomers
 Different in solubility, melting and boiling
points.
Example: Ibuprofen

21. A compound with two identical chirality center
having no optical sensitivity because-
They have two identical chiral parts
One part is optically active and another part
is inactive.
Optically active parts is neutralizes by
inactive parts.
As a result they have no light sensitivity

23. Racemic mixture Meso compound
Mixture of two Equimolar One compound having two
enantiomers identical chiral parts.
Individually light sensitive Though chiral C is present,
but the mixture s neutral the compound is not light
sensitive
Components of the one compound, so two
mixture can be separated. chiral parts can’t be
separated.
Mixture of d-lactic acid and Tartaric acid
l-lactic acid

24.  Stereoisomers are different compounds and
often have different properties.
 Each stereoisomer must have a unique
name.
 The Cahn-Ingold-Prelog convention is used
to identify the configuration of each
asymmetric carbon atom present in a
stereoisomer.
◦ (R) and (S) configuration

25.  The two enantiomers of alanine are:
CO2H CO2H
C C
H H CH3
H3C NH2 H2N
Natural alanine Unnatural alanine
(S)-alanine (R)-alanine

26.  Assign a numerical priority to each group
bonded to the asymmetric carbon:
◦ group 1 = highest priority
◦ group 4 = lowest priority
 Rules for assigning priorities:
◦ Compare the first atom in each group (i.e.
the atom directly bonded to the asymmetric
carbon)
 Atoms with higher atomic numbers have
higher priority

27. Cl 1 3
CH3
3 C 2 C H4
H3C
OCH2CH3 NH2
H 1 F 2
4
Example priorities:
I > Br > Cl > S > F > O > N > 13C > 12C > 3H > 2H > 1H

28.  In case of ties, use the next atoms along the
chain as tiebreakers.
2 CH CH Br
2 2
C H4
3 CH3 2
CH
CH(CH3)2
1
CH(CH3)2 > CH2CH2Br > CH3CH2

29. Y
C Y
C Y C
Y C
 Treat double and triple bonds as if both
Y
C
C
O atoms in the Y Y were duplicated or
Y C bond
C C
O C
triplicated:
H Y C
Y
C C Y Y
OH
H C Y C Y C Y C Y C
CH2OH C Y C
Y C Y C
Y C
O 2 H C C O
Y
C Y C C Y2
O C H
Y 1
C C OH C 1
OH
4 H CH2OH C4 H
Y CH2OH
3 C Y3
Y C

30.  Using a 3-D drawing or model, put the 4th priority
group in back.
 Look at the molecule along the bond between the
asymmetric carbon and the 4th priority group.
 Draw an arrow from the 1st priority group to the 2nd
group to the 3rd group.
◦ Clockwise arrow (R) configuration
◦ Counterclockwise arrow (S) configuration

32.  Theenantiomer with most remote OH from
the CHO to the right is called D(+)
enantiomer
E.g. D(+) glyceraldehyde
 Theenantiomer with most remote OH from the
CHO to the left is called L(-) enantiomer
E.g. L(-) glyceraldehyde

34.  Except for inorganic salts and a few low-
molecular-weight organic substances, the
molecules of living systems are chiral
 Although these molecules can exist as a
number of stereoisomers, generally only one
is produced and used in a given biological
system
 amino acids, nucleosides, carbohydrates
and phospholipids are chiral molecules

35.  Bindingof drugs with enzymes depend
on chirality

37. 1.Ibuprofen
S(+) Ibuprofen R(-)
Ibuprofen

38. 2. Thalidomide

39. 3. Naproxen
S(+) Naproxen R(-) Naproxen

40. 4. Fluoxetine

41. 5. Epinephrine
S(+) Epinephrine R(-)
Epinephrine

43. ROLL- 11 & 13
Semester: 5 th
Batch: 8 th
Department o Pharmacy
Dhaka International
University