4 Isomerism Unit-I.pdf
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Isomerism refers to compounds with the same molecular formula but different structural formulas. There are two main types of isomerism: constitutional isomerism and stereoisomerism. Constitutional isomerism includes structural isomers which have different connectivities of atoms and can be further divided into types like chain isomerism, position isomerism, and functional isomerism. Stereoisomerism refers to isomers with the same connectivity but different orientations in space, and includes cis-trans isomers and enantiomers. The document provides examples and explanations of each type of isomerism.
4 Isomerism Unit-I.pdf
- 1. ISOMERISM Dr. J. SHANMUGAPRIYA ASSISTANT PROFESSOR PG AND RESEARCH DEPARTMENT OF CHEMISTRY THE MADURA COLLEGE Fundamentals in Organic Chemistry By Dr.J.Shanmugapriya
- 2. Isomerism • The term ‘isomerism’ was given by Berzelius, and its represents of existence of two or more compounds with the same molecular formula but different structure and properties (physical, chemical, or both). • The existence of isomers is one of the reasons why such a huge array of different organic compounds exist. • Other reasons for the diversity of organic compounds include (i) carbon chain catenation i.e. the ability of carbon chains to link together and (ii) the formation of stable bonds with elements such as oxygen, nitrogen, hydrogen etc. Fundamentals in Organic Chemistry By Dr.J.Shanmugapriya
- 3. • Compounds exhibiting this isomerism are called isomers. The difference in properties of two isomers is due to difference in (bond connectivity or spatial arrangement) the arrangement of atoms within their molecules. • Isomerism in organic chemistry is a phenomenon shown by two or more organic compounds having the same molecular formula but different properties due to difference in arrangement of atoms along the carbon skeleton (structural isomerism) or in space (Stereo isomerism). Fundamentals in Organic Chemistry By Dr.J.Shanmugapriya
- 4. Isomerism is broadly divided into two types. i. Constitutional isomerism, ii.stereoisomerism. Fundamentals in Organic Chemistry By Dr.J.Shanmugapriya
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- 6. STRUCTURAL ISOMERISM • This type of Isomerism is classifiedinto 6 types- 1. Chain or nuclear or skeletal isomerism 2. Positional Isomerism. 3. Functional Isomerism. 4. Ring Chain Isomerism. 5. MetamerismIsomerism. 6. Tautomerism Isomerism Fundamentals in Organic Chemistry By Dr.J.Shanmugapriya
- 7. Chain or Nuclear or Skeletalisomerism • The same molecular formula represents two or more compounds . It occurs when carbon atoms are linked to the main chain in different ways. These isomers differ in the way in which the carbon atoms are bonded to each other in a carbon chain or in other words isomers have similar molecular formula but differ in the nature of the carbon skeleton (ie. Straight or branched) • For example: There are two structural isomers of C4H10. One is a straight chain molecule where all the carbon atoms are in a single row. The other is a branched molecule where three carbon atoms are in a row and one carbon atom sticks out of the main chain. • Fundamentals in Organic Chemistry By Dr.J.Shanmugapriya
- 8. Isomers show similar chemical properties because the same functional group is present. slightly differentphysical properties-more branching = lower boiling point Fundamentals in Organic Chemistry By Dr.J.Shanmugapriya
- 9. Position isomerism If different compounds belonging to same homologous series with the same molecular formula and carbon skeleton, but differ in the position of substituent or functional group or an unsaturated linkage are said to exhibit position isomerism. Fundamentals in Organic Chemistry By Dr.J.Shanmugapriya
- 10. Molecule has the same carbon skeleton-molecule has the same functional group... BUT the functional group is in a different position have similar chemical properties / different physical properties Fundamentals in Organic Chemistry By Dr.J.Shanmugapriya
- 11. Functional isomerism Different compounds having same molecular formula but different functional groups are said to exhibit functional isomerism. Fundamentals in Organic Chemistry By Dr.J.Shanmugapriya
- 13. Metamerism • The same molecular formula represents two or more compounds. • It differs in the nature of the alkyl groups attached to the same functional group. • Example, Diethyl ether and Methyl propyl ether are metamerical isomers. This type of isomerism is a special kind of structural isomerism arises due to the unequal distribution of carbon atoms on either side of the functional group or different alkyl groups attached to the either side of the same functional group and having same molecular formula. • This isomerism is shown by compounds having functional group such as ethers, ketones, esters and secondary amines between two alkyl groups. Fundamentals in Organic Chemistry By Dr.J.Shanmugapriya
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- 15. RING CHAIN ISOMERISM • The same molecular formula represents two or more compounds. • It differs in the mode of linkage of carbon atoms. • The isomers have either open chain or closed chain. • Example, Propene and cyclopropane are ring chain isomers. In this type of isomerism, compoundshaving same molecular formula but differ in terms of bonding of carbon atom to form open chain and cyclic structures for eg: Fundamentals in Organic Chemistry By Dr.J.Shanmugapriya
- 16. Tautomerism • It is a special type of functional isomerism in which a single compound exists in two readily inter convertible structures that differ markedly in the relative position of at least one atomic nucleus, generally hydrogen. The two different structures are known as tautomers. • There are several types of tautomerism and the two important types are dyad and triad systems. • Dyad system: In this system hydrogen atom oscillates between two directly linked polyvalent atoms. • Eg: In this example hydrogen atom oscillates between carbon & nitrogen atom Fundamentals in Organic Chemistry By Dr.J.Shanmugapriya
- 17. Triad system: In this system hydrogen atom oscillates between three polyvalent atoms. It involves 1,3 migration of hydrogen atom from one polyvalent atom to other within the molecule. The most important type of triad system is keto–enol tautomerism and the two groups of tautomers are keto form and enol-form. The polyvalent atoms involved are one oxygen and two carbon atoms. Enolisation is a process in which keto-form is converted to enol form. Both tautomeric forms are not equally stable. The less stable form is known as labile form Nitro-aci tautomerism. Fundamentals in Organic Chemistry By Dr.J.Shanmugapriya
- 18. STEREOISOMERISM This type of Isomerism differs in the spatial arrangement of atoms or groups. It is of two types – 1. Geometrical Isomerism. 2. Optical Isomerism. GEOMETRICAL ISOMERISM • The same molecular formula represents two or more compounds. It differs in the spatial arrangement of atoms or groups around carboncarbon double bond. • It is of two types-If same group are on same side then, it is called ‘cis’ isomers and if it is on opposite sides, then it is called ‘trans’ isomers. • Example, cis-2-butene and trans-2-butene are ‘cis’ and ‘trans’ isomers. Fundamentals in Organic Chemistry By Dr.J.Shanmugapriya
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- 26. OPTICAL ISOMERISM • Optical Isomers are named like this because of their effect on plane polarized light. • Optical Isomers, which are non-superimposable mirror images of each other, are called Enantiomers. Example, d-Alanine and l-Alanine, lactic acid etc. Fundamentals in Organic Chemistry By Dr.J.Shanmugapriya
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