This document discusses different types of stereoisomers, including geometrical isomers that differ in the spatial arrangement of atoms or groups about a double bond. It describes cis-trans isomerism, which refers to identical groups on the same side (cis) or opposite sides (trans) of a double bond. It also discusses E-Z notation and priority rules for assigning E or Z configurations based on atomic number and mass of substituents. Syn and anti notation for stereoisomers of oximes is also introduced. Examples of stereochemistry in vision and drug action are provided.

1. Stereochemistry of
organic compounds
Geometrical isomerism : geometrical isomers

3. Stereoisomers
Isomers which have same structural formula but
differ in the relative arrangement of atoms or groups
in space

4. Geometrical isomerism
• Isomers which have same structural formula but
differ in spatial arrangement of atoms or groups
about the double bond
• Nomenclature:
• Cis- trans
• E-Z
• Anti-syn

5. two requirements for cis-trans isomerism:
Rotation must be restricted in the molecule.
There must be two nonidentical groups on each doubly bonded carbon atom

6. Cis- trans isomerism
Identical group on same side: cis
Identical group on opposite side: trans

7. Cis-trans isomerism also occurs in cyclic compounds. In ring structures,
groups are unable to rotate about any of the ring carbon–carbon bonds.
Therefore, groups can be either on the same side of the ring (cis) or on
opposite sides of the ring (trans).

8. What if you have the compound
Cis
Trans
Cis
Trans

9. E and Z notation
• Based on priority of groups attached to double
bonded carbon
• (E)- :entgegen
• the higher priority groups are on opposite sides of the
double bond.
• (Z)- :zusammen
• the higher priority groups are on the same side of the
double bond.

10. Priority of groups
1
• Higher atomic number, higher priority
2
• Higher mass number
3
• Atoms/ groups attached
• Double bonds are duplicated

11. E and Z notation
Z E

12. Syn and anti notation
• For stereoisomeric oximes

13. Stereochemistry in vision process
11-cis retinal
covalently bound to an opsin
signaling protein to form a
visual pigment molecule
all-trans retinal
straightening of the polyene
chain activates the opsin

14. Drug action: Diethylstilbestrol
(DES)
effective ineffective
nonsteroidal estrogen medication

15. Pheromones