CBSE Class 12-science Answered

The existance of a molecule in different structural forms all having the same molecular formula is called isomerism.

Types -

 

1. Chain isomerism - If the length of the isomeric forms varies it is called chain isomerism. they can be either straight chain or branched chaains.

eg. Molecular formula having C₄H₁₀ is called butane they can have normal straight chain and a branched (iso) form.

Butane has two structural isomers.

 

  n- butane

2. Functional isomerism - if same molecuar formula can have different types of functional group.

Eg - Ethanol (C₂H₅OH) have -OH as functional group whereas ethers have -O- as functional group but both have same MF as C₂H₆O.

 

3. Metamerism - If there is shifting of 1CH3 group in case of ethers it is metamerism.

eg - CH₃-CH₂-O-CH₂-CH₂-CH₃  & CH₃-O-CH₂-CH₂-CH₂-CH₃ both have same MF.

 

4. Positional isomers - If the position of the functional group changes in a molecule it is positional isomerism

Eg - ClCH₂CH₂CH₂CH₃ & CH₃CH(Cl)CH₂CH₃

 

5. Geometrical Isomerism - If the relative positions of the priority groups are same or different with respect to the double bond it can either be cis form or trans form.

Eg - Cis-Butene and Trans-butene

 

 

6. Stereoisomerism - Also called space isomerism depends on the rotation of a molecule in a polarimeter.

 

7. Tautomerism - Resonance between sigma and pie bonds like formation of enol from aldehydes.