Isomerism in Organic Chemistry:

Isomerism is compounds having same molecular formula but they differ in physical or chemical properties or both.

There are two types of isomerism Structural isomerism and stereoisomerism.

Structural isomerism occurs due to the difference in the arrangement of atoms in a molecule (without referring to space), type of linkage and the atoms which are linked to each other in a molecule.

Stereo isomerism occurs out of arrangement of atoms in a molecule with reference to each other in spaceThey have the same structure differ in the way the atoms are oriented in the space.

Structural isomerism is divided into 5kinds 

• Nuclear isomerism
• position isomerism
• functional isomerism
• metamerism
• tautomerism

Nuclear isomerism

The molecular formula will be the same. It differs in the arrangement of carbon chain C5H12 pentane normal pentane and iso pentane are examples.

Position isomerism

The same substituent will occupy different position in organic compounds

CH₃-CH₂- CH₂Cl Normal chloro propane

CH₃- CHCl- CH₃ iso chloro propane Or 2 chloro propane

Functional isomerism

The same molecular will express two different compound with different functional groups

C₂H₆O

C₂H₅OH ethyl alcohol

CH₃- O- CH₃ dimethyl ether

Metamerism

The alkyl groups attached to the functional group will be different.

C₄H₁₀ O

C₂H₅ - O - C₂H₅ (Diethyl ether)

CH₃ - O - CH₂ - CH₂ - CH₃ (methyl propyl ether)

CH₃ - O - CH - (CH₃)₂ methyl iso propyl ether are metamers.

Stereo isomerism is divided into two types

Geometrical and optical isomerism.

The isomers in which similar groups lie on the same side is called Cis isomer.

The other in which the similar groups lie in opposite direction is called "trans isomer"

This isomerism is called "cis-trans isomerism. Stablity of cis isomer is lower than the trans isomers.