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Structural IsomerismStructural Isomerism

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22IsomersIsomers Structural 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.

33IsomersIsomers Example 1-chloropropane and 2-chloropropane has

different structural formula.

44IsomersIsomers Example cis-2-butene and trans-2-butene has same

structural formula.

55IsomersIsomers Type of Structural Isomers.

1. Chain Isomerism

2. Positional Isomerism

3. Functional Isomerism

4. Metamerism.

5. Tautomerism

66IsomersIsomers 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

77IsomersIsomers

Example1.Ethylbenzene and o-Xylene.

2. Butanoicacid and 2-methylpropanoicacid,

88IsomersIsomers 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

99IsomersIsomers

Example 1. 1-butanol & 2-butanol

2. O-Xylene & m-Xylene.

1010IsomersIsomers Functional Isomers: Isomers which have

different functional group.

Note 1. No of atoms same

2. No. of D.U same.

3. Functional groups differs

1111IsomersIsomers

Example 1. 1-butanol & Ethoxyethane

2. Ethanal and Oxirane.

1212IsomersIsomers 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.

1313IsomersIsomers

Example 1. Methoxypropane & Ethoxyethane

2. Ethylethanoate and Methylpropanoate.

1414IsomersIsomers 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.

1515IsomersIsomers Only the stable tautomeric form is counted

while counting isomers. Type-1 Keto- Enol tautomerism. Example Cyclohexanone and cyclohexenol

1616IsomersIsomers Type-2 Nitro-Acinitro Example nitrocyclohexane and

acinitrocyclohexene

1717IsomersIsomers Type-3 Imine - En-amine Example cyclohex-1-en-1-amine

and cyclohexanimine

1818IsomersIsomers Type-4 Cyano - isocyano Example Cyanicacid and isocyanicacid.

1919IsomersIsomers Type-4 Cyano - isocyano Example Cyanicacid and isocyanicacid.

2020IsomersIsomers There are several types of tautomerism, There are several types of tautomerism,

which will be discussed in details in which will be discussed in details in carbanion section of reaction mechanism.carbanion section of reaction mechanism.

2121Exercise-1Exercise-1 Identify the relationship between given pair

of compounds.

2222Exercise-1Exercise-1 Answer:- Functional isomers.

2323Exercise-2Exercise-2 Identify the relationship between given pair of

compounds.

2424Exercise-2Exercise-2 Answer- Chain isomerism.

2525Exercise-3Exercise-3 Identify the relationship between given pair

of compounds.

2626Exercise-3Exercise-3 Answer :- Different compounds Number of carbon as well as functional

group differs.

2727Exercise-4Exercise-4 Identify the relationship between given pair

of compounds.

2828Exercise-4Exercise-4 Answer :- Metamers. Number of carbon along hetro atom differs.

2929Exercise-5Exercise-5 Identify the relationship between given pair of

compounds.

3030Exercise-5Exercise-5 Answer :- Functional isomers A has Aldehydes group but B has ketone.

3131Exercise-6Exercise-6 Identify the relationship between given pair of

compounds.

3232Exercise-6Exercise-6 Answer :- Positional isomers

3333Exercise-7Exercise-7 Identify the relationship between given pair of

compounds.

A .Hexane-2-ol B. Heptane-2-ol

3434Exercise-7Exercise-7 Answer :- Homologous compounds.

Compounds with different carbon but with same functional groups are called homologous compounds.

3535Exercise-8Exercise-8 Identify the relationship between given pair

of compounds.

A. Methylcyclopropane B. Cyclobutane

3636Exercise-8Exercise-8 Answer :- Chain isomers

3737Exercise-9Exercise-9 Identify the relationship between given pair

of compounds.

A. 1-Butene B. cyclobutane

3838Exercise-9Exercise-9 Answer :- Functional isomers (Some

literature also mention ring chain isomerism.)

3939Exercise-10Exercise-10 Identify the relationship between given pair of

compounds.

4040Exercise-10Exercise-10 Answer :- Metamers.

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