Isomerism

Organic chemistry, Organic compounds, Isomerism

1. ISOMERISM By Dr. Alhaiqa Farooqi R Ph , Pharm D , MS, FCPS , MCPS

2. Compounds that have same molecular formula but differ from each other in physical or chemical properties are called ISOMERS & the phenomenon is called ISOMERISM . Isomers have same molecular formula but difference in their properties must be due to different modes of combination or arrangement of atoms within a molecule.

3. TYPES OF ISOMERISM Two main types STRUCTURAL ISOMERISM STEREOISOMERISM

4. STRUCTURAL ISOMERISM When the isomerism is due to difference in arrangement of atoms within the molecule, without any reference to space, the phenomenon is called Structural isomerism. Structural isomers are the compounds that have same molecular formula but different structural formulas.

5. TYPES OF STRUCTURAL ISOMERISM Five types Chain isomerism Position isomerism Functional isomerism Metamerism Tautomerism

6. CHAIN ISOMERISM Same molecular formula but differ in the order in which carbon atoms are bonded to each other. E.g.

7. POSITION ISOMERISM Same molecular formula but differ in the position of functional group on carbon chain.

8. FUNCTIONAL ISOMERISM Same molecular formula but different functional groups.

9. METAMERISM This type of isomerism arises due to unequal distribution of carbon atoms on either side of the functional group.

10. TAUTOMERISM When two structural isomers are mutually interconvertible & exist in dynamic equilibrium they are called tautomers & the phenomenon is called tautomerism. Uracil

11. Acetone exhibits tautomerism & may be represented as an equilibrium mixture of two isomers. Here the keto form changes to enol form by migration of a proton to carbonyl oxygen, the pair of electron shifts from C-H bond to C-C bond.

12. How do tautomerism differ from resonance? Tautomerism involves equilibrium between structures & different tautomeric forms have real existence. Tautomerism involves movement of both electrons & atoms whereas resonance structures differ in respect of position of electrons only.

13. Keto-Enol Tautomerism Aldehydes , ketones & other carbonyl compounds ( e.g. esters) exhibit this special type of tautomerism. It involves migration of proton from α - carbon to carbonyl oxygen. The tautomer containing carbonyl group is designated as Keto form & the other containing hydroxy group attached to doubly bonded carbon is referred to as Enol form( alk EN e + alcoh OL )

14. EXAMPLES OF TAUTOMERISM Ethyl acetoacetate

15. THANKS