Geometrical isomerism occurs when compounds contain a carbon-carbon double bond and the groups attached to the double bonded carbons are different. The key types of geometrical isomers are cis-trans and E-Z isomers. The configuration of geometrical isomers can be determined through methods like cyclization reactions, conversion to compounds of known configuration, optical activity measurements, differences in physical properties, and stereoselective reactions.

1. POC-2
CONTINUOUS ASSESSMENT-1
Geometrical
Isomerism
GEOMETRICAL
ISOMERISM
GROUP NO 12
FROM ROLL NO 89 to 96

3. Isomerism
 The organic compounds having the same
molecular formula but different structure is
known as Isomers.
 In another words , the organic compounds having
the same molecular formula but different
arrangements of carbon atoms in them are known
as Isomerism

4. Classification of Isomers :-

7. Geometrical Isomerism

8. Geometrical Isomerism

9. Conditions of Geometrical
isomerism:
 The molecule must have C=C double bond.
 The two atoms or groups attached to the doubly
bonded carbon atom must be different.

10. Geometrical Isomerism

13. E- Z Nomenclature
 When cis - trans system fails to give an unambigous name , the
E–Z system is used .
 Steps for nomenclature of E-Z system :-
1. Consider each carbon of the double bond seperately
2. Assign the Cohn-Ingol-Prelog (CIP) priorities to the group
attached to each carbon.
3. If the groups of high priorities are on the same side , the
component is Z. ( In Greek Z = Zussamen means together. )
4. If the groups of high priorities are in the opposite side , the
componeny is E . ( In Greek , E = Entagen means opposite .)

14. Syn – Anti Nomenclature
 When two atom are added to the same side , it is known as SYN
relationship.
 When two atom are added to the opposite side , it is known as ANTI
relationship.
 For example , when C=N is formed by the reaction of aldehyde with
NH2 –G then H on carbon and constituent on nitrogen are in same side
then configuration is SYN and when constituent on nitrogen are in
opposite side then the configuration is ANTI

15. Methods of determination of configuration of
Geometrical Isomers
1. Methods of Cyclization .
2. By converting into the compounds of known configuration
3. Optical Activity.
4. Method based on physical properties.
5. By stereoselective.
6. Method of formation of solid solution.

16. 1. METHOD OF CYCLIZATION.
 This method is applied in which either of the form
capable of forming a ring .
 Principle :-
The molecular reaction occurs easily
when the reacting groups are closed together .

17.  For example ,
Among two acids , Mallic and Fumaric
only the former give anhydride on gentle heating so
in Malic acid the two reactive groups ( -COOH ) are
closed together and hence it is cis and Fumaric acid
is trans .

18. 2.By converting into the compounds of
known configuration:
Geometrical Isomers of pair can be converted into a
compound of known configuration
Na,amalgum and water or
Zn and acetic acid

19. 3.Optical Activity:
 Due to presence or absence of an element of symmetry one form may
be optically inactive and other optically active.
 For Example:
• Cis Hexahydrophthalic Acid shows Plane of Symmetry and hence it is
Optically Inactive while Trans Hexahydrophthalic Acid does not shows
Plane of Symmetry hence it is Optically Active.

20. 4] Method of formation of solid solution-
•Applicable in such compound whose structure is known
and saturated derivatives are available.
•If the shape of isomer is same to that of saturated
compound, it can form solid solution.

21. 5] By Stereoselective Reaction-
A reaction in which one stereoisomer is formed predominantly or
excessively out of several stereoisomers possibilities is called a
stereoselective reaction. Such a reaction is said to display
stereoselectivity. In this one stereoisomer is formed more rapidly thus
resulting in a selective reaction.
A Stereoelectronic requirement of the mechanism of a stereoselective
reaction offers alternatively parts so that the reaction proceeds either
via the most favourable path or via the path which gives the most stable
stereoisomers as the major product.

22. BASED ON PHYSICAL PROPERTIES
1. In geometrical isomerism, free rotation of bonds in the
compound should be blocked.
This is possible only in –
compound having double bond.
cyclic compounds.
2. The boiling point of trans-isomer is greater than the cis-
isomer. The Latin prefixes cis- and trans- indicate how the
groups attached to the double bond are arranged in space
with the cis meaning the same side and trans meaning
opposite side.

23. 3. cis-isomers have more stability then the trans-isomer
because cis-isomer have more internal energy. The
dipoles of trans substituents cancal each other out,
which the dipoles of cis substituents are additive.
4. Cis-isomers have more solubility, dipole moment and
higher refractive index than that of trans isomers.
Trends in these differences are attributed to the effect
of the overall dipole moment.
5. In the case of a dicarboxylic acid, cis-isomer cam easily
form acid anhydrases by releasing one molecule of
water. Trans-isomer never does it. E.g. maleic acid &
fumaric acid.

24. Method based on physical properties
 Dipole moment
 Melting point
 Boiling point
 Solubility
 Refractive index
 Acid strength
 X-ray
 Electron diffraction
 Spectroscopy

25. STEREOSPECIFIC REACTION
 . - A Reaction in which a particular
stereoisomers react to give one specific
stereoisomer of the product is called a
stereospecific reaction. Such a reaction is
said to display stereospecificity. A
stereospecific reaction gives a different
stereoisomers of the starting material.
This is a reaction in which the
stereochemistry of the reactants controls
the outcome of the reaction