Geometrical Isomerism

By Students of Sir Dr. M.S. GOSAVI COLLEGE OF PHARMACEUTICAL EDUCATION AND RESEARCH, NASHIK.

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

2. 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

3. Classification of Isomers :-

4. Geometrical Isomerism

5. Geometrical Isomerism

6. 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.

7. Geometrical Isomerism

8. 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 :- Consider each carbon of the double bond seperately Assign the Cohn-Ingol-Prelog (CIP) priorities to the group attached to each carbon. If the groups of high priorities are on the same side , the component is Z. ( In Greek Z = Zussamen means together. ) If the groups of high priorities are in the opposite side , the componeny is E . ( In Greek , E = Entagen means opposite .)

9. 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

10. Methods of determination of configuration of Geometrical Isomers Methods of Cyclization . By converting into the compounds of known configuration Optical Activity. Method based on physical properties. By stereoselective. Method of formation of solid solution.

11. 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 .

12. 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 .

13. 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

14. 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.

15. 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.

16. 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.

17. 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. 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.

18. 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. 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. 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.

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

20. 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