Organic Chemistry —Part 1.

in #esteem6 years ago (edited)

ISOMERISM:

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Image-source by Paginazero under Public domain

Compounds having same molecular formula but different physical and chemical properties are known as ISOMERS and the phenomenon is known as ISOMERISM.

  • Isomerism is of following two types:

  • 1: Structural Isomerism.

  • 2: Stereo Isomerism.

  • (a):Structural Isomerism (or Constitutional Isomerism):-
    Compounds having same molecular formula but different structural formula are called structural isomers.
    (OR)
    Compounds having same molecular formula but different properties due to difference in their structures are called structural isomers and the phenomenon is known as Structural Isomerism.

Structural Isomerism is of different types:

  • 1:Chain or Nuclear or Skeltal Isomerism:-
    Compounds having same molecular formula but different arrangements of carbon atoms within the parent chain are known as Chain Isomers and the phenomenon is known as Chain Isomerism.

  • 2:Positional Isomerism:-
    Compounds having same molecular formula but different in the position of either multiple bonds or functional group or substituents are known as Positional Isomers and the phenomenon is known as Positional Isomerism.

  • 3:Functional Isomerism:-
    Compounds having the same molecular formula but different functional groups are known as Functional Isomers and the phenomenon is known as Functional Isomerism.

  • 4:Ring-Chain Isomerism:-
    Compounds having same molecular formula but one possessing an open chain structure and another a close chain structure are called Ring-Chain Isomer and the phenomenon is known as Ring-Chain Isomerism.

  • 5:Metamerism:-
    Compounds having same molecular formula but alkyl groups or different arrangements of carbon atoms around a bi-valent functional group such that; Ether,Thioether,2°-amine,Ketone,etc are known as Metamers and the phenomenon is known as Metamerism.
    Metamers are also positional isomers and they are also sometimes referred to ad special type of positional isomers.

  • 6:Tautomerism:-
    { Different Names:- Desmotropism,Allelotropism, Kryptomism,Merotropism,Ionotropy,Cationotropy,Prototropy,Pseudomerism,Reversible Isomerism and Dynamic Isomerism.}

    Compounds having same molecular formula but different functional groups or different structures due to wandering nature of mobile Hydrogen atom between two polyvalent atoms within the molecules are called Tautomers and the phenomenon is known as Tautomerism.

  • Types of Tautomerism:-
    It is of following 3 types:

    • Open system.
    • Closed system.
    • Valance system.
      • 1: Open System:-
        It also contains two types: Prototropy and Anionotropy.
        • Prototropy:- That type of Tautomerism which involves migration of a proton between two polyvalent atoms within the molecule.
        • Anionotropy:- That type of Tautomerism which involves migration of anion or an atom or a group capable of forming a stable anion.
          This type of Tautomerism is very rare and is generally studied under ALLYLIC Rearrangements.
  • PROTOTROPY is further of 2 types:-
    1: DYAD system of Prototropy:- It is that type of tautomerism during which Hydrogen(p+) migrates between two polyvalent positions which are adjusant with respect to each other.
    (or)
    It is that type of Tautomerism which involves 1,2–Hydrogen(p+) [means adjusant] migration between two polyvalent atoms within the molecule.
    2: TRAID system of Prototropy:- It is that type of Tautomerism which involves 1,3–Hydrogen(p+) migration between two polyvalent atoms within the molecule.

Keto-Enol Tautomerism:-

That type of tautomerism which involves 1,3–Hydrogen(p+) migration between two polyvalent atoms within the molecule in such a way so that a Keto form gets converted into an Enol form or vice-versa.

Conditions of Keto-Enol Tautomerism:-

  • Their must be atleast 1-sp³ hybridise carbon containing atleast 1 Hydrogen atom attatched to COH or CO or COOR.This condition is applicable only for Keto-form.
  • Their must be atleast 1-OH group attatched to C=C (except phenol).This condition is applicable only for Enol-form.

REFERANCE:-



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