Isomerism Final

7/29/2019 Isomerism Final

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N.J.SIR

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IIT-JEE Chemistry by N.J. Sir ORGANIC chemistry

ISOMERISM


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ISOMERISMIn the study of organic chemistry we come across many cases when two or more compounds are madeof equal number of like atoms. A molecular formula does not tell the nature of organic compound;sometimes several organic compounds may have same molecular formula. These compoundspossess the same molecular formula but differ from each other in physical or chemical properties, arecalled isomers and the phenomenon is termed isomerism (Greek, isos = equal; meros = parts). Sinceisomers have the same molecular formula, the difference in their properties must be due to differentmodes of the combination or arrangement of atoms with in the molecule. Broadly speaking, isomerism

is of two types.i) Structural Isomerismii) Stereoisomerismi) Structural isomerism: When the isomerism is simply due to difference in the arrangement of atoms

with in the molecule without any reference to space, the phenomenon is termed structural isomerism. Inother words, while they have same molecular formulas they possess different structural formulas. Thistype of isomerism which arises from difference in the structure of molecules, includes:a) Chainb) Positional Isomerismc) Functional Isomerismd) Metamerism ande) Tautomerism

f) Ring-chain Isomerismii) Stereoisomerism: When isomerism is caused by the different arrangements of atoms or groups in

space, the phenomenon is called Stereoisomerism (Greek, Stereos = occupying space). Thestereoisomers have the same structural formulas but differ in the spatial arrangement of atoms orgroups in the molecule. In other words, stereoisomerism is exhibited by such compounds which haveidentical molecular structure but different configurations.Stereoisomerism is of three types :a) Conformation b) Geometrical. c). OpticalThus various types of isomerism could be summarised as follows.

ISOMERISM

STRUCTURAL

ISOMERISM

STEREOISOMERISM

GEOMETRICAL

ISOMERISM

FUNCTIONAL

ISOMERISM

POSITIONAL

ISOMERISM

CHAIN

ISOMERISM

METAMERISM TAUTOMERISM

OPTICAL

ISOMERISM

CONFORMATION

RING CHAIN

Chain IsomerismThis type of isomerism arises from the difference in the structure of carbon chain which forms the nucleus ofthe molecule. It is, therefore, named as chain, or Skeletal isomerism. For example, there are known twobutanes which have the same molecular formula (C4H10) but differ in the structure of the carbon chains in theirmolecules.

CH3CH2CH2CH3 H3CCHCH3n-butane |

CH3isobutane


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