Isomerism 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)
Structural isomerism:
1. Chain isomerism: These isomers arise because of the possibility
of branching in carbon chains. For example, there are two isomers of butane,
C4H10. In one of them, the carbon atoms lie in a "straight chain"
whereas in the other the chain is branched.
2. Positional isomers: The isomers that have the same carbon
skeleton and the same functional groups but differ from each other in the
location of the functional groups on the carbon chain.
3. Functional group isomerism:
The isomers contain different
functional groups - that is, they belong to different families of compounds
(different homologous series).
Ex:
4. Metamerism: The metamerism arises when different alkyl groups are
attached to same functional group.
Ex:
Stereo isomerism:
The isomerism which arises due to different spatial arrangements
of atoms or groups is called stereo isomerism. It is broadly divided into:
1.
Geometrical isomerism
2.
Optical isomerism
1. Geometrical isomerism:
The geometrical isomerism arises when
atoms or groups are arranged differently in space due to restricted rotation of
a bond or bonds in a molecule.
2. Optical isomerism: Involves an atom, usually carbon, bonded to
four different atoms or groups of atoms. They exist in pairs, in which one
isomer is the mirror image of the other.
Ex: butan-2-ol
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