1. Structural isomers have the same molecular formula but different structural formulas, meaning different bond arrangements or connectivity of atoms. 2. There are several types of structural isomers including chain isomers, positional isomers, functional isomers, metamers, and tautomers. 3. Tautomers are a type of functional isomer that can interconvert in solution through the rapid movement of hydrogen atoms or other groups between functional groups.

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2. Isomers Structural Isomers: Isomers ,which have same molecular formula, but different structural formula are called structural isomers. Different Structural formula means Different bond pattern or Different arrangement of  bonds or Different connectivity of atoms. The key to organic chemistry is crystal clear understanding of different terms used.

3. Isomers Example 1-chloropropane and 2-chloropropane has different structural formula.

4. Isomers Example cis -2-butene and trans -2-butene has same structural formula.

5. Isomers Type of Structural Isomers. 1. Chain Isomerism 2. Positional Isomerism 3. Functional Isomerism 4. Metamerism. 5. Tautomerism

6. Isomers Chain Isomerism: Isomers which have same functional groups but different arrangement of carbon skeleton in principal chain or side chains are chain isomers. Note 1. No of atoms same 2.No. of D.U same. 3. Functional groups Same. 4. Carbon skeleton different

7. Isomers Example1.Ethylbenzene and o-Xylene. 2. Butanoicacid and 2-methylpropanoicacid,

8. Isomers Positional Isomerism: Isomers which have same functional groups ,same arrangement of carbon skeleton but different position of functional groups or substituents. Note 1. No of atoms same 2.No. of D.U same. 3. Functional groups Same. 4. Carbon skeleton Same 5.Position of F.G, differs

9. Isomers Example 1. 1-butanol & 2-butanol 2. O-Xylene & m-Xylene.

10. Isomers Functional Isomers: Isomers which have different functional group. Note 1. No of atoms same 2. No. of D.U same. 3. Functional groups differs

11. Isomers Example 1. 1-butanol & Ethoxyethane 2. Ethanal and Oxirane.

12. Isomers Metamers: Isomers which have different carbonchain lenth along a functional group withhetro atom (Ex- Ethers, Esters, secondary amines, tertiary amines , Secondary amides etc. Note 1. No of atoms same 2. No. of D.U same. 3. Functional groups same. 4. Number of carbon differs along hetro atoms.

13. Isomers Example 1. Methoxypropane & Ethoxyethane 2. Ethylethanoate and Methylpropanoate.

14. Isomers Tautomers: A type of functional Isomers which exist in rapid equilibrium in solution are called functional isomers. Tautomers are interconvertable in solution Tautomers usually differs in position of H atom at  carbon. Interconversion of tautomers can be catalysed. Tautomers can’t be seperated in solution at normal temperature. The more stable form dominates in equillibrium.

15. Isomers Only the stable tautomeric form is counted while counting isomers. Type-1 Keto- Enol tautomerism. Example Cyclohexanone and cyclohexenol

16. Isomers Type-2 Nitro-Acinitro Example nitrocyclohexane and acinitrocyclohexene

17. Isomers Type-3 Imine - En-amine Example cyclohex-1-en-1-amine and cyclohexanimine

18. Isomers Type-4 Cyano - isocyano Example Cyanicacid and isocyanicacid.

19. Isomers Type-4 Cyano - isocyano Example Cyanicacid and isocyanicacid.

20. Isomers There are several types of tautomerism, which will be discussed in details in carbanion section of reaction mechanism.

21. Exercise-1 Identify the relationship between given pair of compounds.

22. Exercise-1 Answer:- Functional isomers.

23. Exercise-2 Identify the relationship between given pair of compounds.

24. Exercise-2 Answer- Chain isomerism.

25. Exercise-3 Identify the relationship between given pair of compounds.

26. Exercise-3 Answer :- Different compounds Number of carbon as well as functional group differs.

27. Exercise-4 Identify the relationship between given pair of compounds.

28. Exercise-4 Answer :- Metamers. Number of carbon along hetro atom differs.

29. Exercise-5 Identify the relationship between given pair of compounds.

30. Exercise-5 Answer :- Functional isomers A has Aldehydes group but B has ketone.

31. Exercise-6 Identify the relationship between given pair of compounds.

32. Exercise-6 Answer :- Positional isomers

33. Exercise-7 Identify the relationship between given pair of compounds. A .Hexane-2-ol B. Heptane-2-ol

34. Exercise-7 Answer :- Homologous compounds. Compounds with different carbon but with same functional groups are called homologous compounds.

35. Exercise-8 Identify the relationship between given pair of compounds. A. Methylcyclopropane B. Cyclobutane

36. Exercise-8 Answer :- Chain isomers

37. Exercise-9 Identify the relationship between given pair of compounds. A. 1-Butene B. cyclobutane

38. Exercise-9 Answer :- Functional isomers (Some literature also mention ring chain isomerism.)

39. Exercise-10 Identify the relationship between given pair of compounds.

40. Exercise-10 Answer :- Metamers.

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