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
5.
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.
7.
8.
9. The Light whose electric fields oscillate in
single plane.
10.
11.
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
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
22.
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
31.
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
33.
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
