Notes On Isomerism - CBSE Class 11 Chemistry
The existence of two or more compounds with the same molecular formula but different properties is known as isomerism. The compounds themselves are called as isomers. Isomerism can be of two types: Structural isomerism                 → Chain isomerism                 → Position isomerism                 → Function group isomerism                 → Metamerism Stereoisomerism (i) Structural isomerism: A compound having same molecular formula but different structures i.e. the way by which the atoms are linked is called as structural isomers and the phenomena is known as structural isomerism. (a) Compounds that have the same molecular formula but different Carbon chain that is straight chain or branched chain are known as chain isomers and the phenomena is known as chain isomerism. Ex: Butane and isobutane the molecular formula is same but their structures are different (as they differ in their chain). (b) Compounds that have the same molecular formula same chain  but which differ in the position of the substituent (or) functional group are known as position isomers and the phenomenon is known as position isomerism. Ex: Structures possible with molecular formula with C3H8O.   (c) The compounds having same molecular formula but different functional group are called as functional isomers and the phenomenon is known as functional isomerism. Ex: Structures possible with Molecular formula with C3H6O. (d) The compounds having same molecular formula but different alkyl group attached to the same functional group are called as metamers and the phenomenon is known as metamerism. Ex: Structures possible with C4H8O   (ii) Stereoisomerism: The isomers which possess the same structural formula but differ in three dimensional arrangement of atoms (or) groups in space within the molecule are known as stereo isomerism.

#### Summary

The existence of two or more compounds with the same molecular formula but different properties is known as isomerism. The compounds themselves are called as isomers. Isomerism can be of two types: Structural isomerism                 → Chain isomerism                 → Position isomerism                 → Function group isomerism                 → Metamerism Stereoisomerism (i) Structural isomerism: A compound having same molecular formula but different structures i.e. the way by which the atoms are linked is called as structural isomers and the phenomena is known as structural isomerism. (a) Compounds that have the same molecular formula but different Carbon chain that is straight chain or branched chain are known as chain isomers and the phenomena is known as chain isomerism. Ex: Butane and isobutane the molecular formula is same but their structures are different (as they differ in their chain). (b) Compounds that have the same molecular formula same chain  but which differ in the position of the substituent (or) functional group are known as position isomers and the phenomenon is known as position isomerism. Ex: Structures possible with molecular formula with C3H8O.   (c) The compounds having same molecular formula but different functional group are called as functional isomers and the phenomenon is known as functional isomerism. Ex: Structures possible with Molecular formula with C3H6O. (d) The compounds having same molecular formula but different alkyl group attached to the same functional group are called as metamers and the phenomenon is known as metamerism. Ex: Structures possible with C4H8O   (ii) Stereoisomerism: The isomers which possess the same structural formula but differ in three dimensional arrangement of atoms (or) groups in space within the molecule are known as stereo isomerism.

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