This is the existence of or more compounds with the same molecular formulae but different structural formulae. There are five types of structural isomerism:
- Chain isomerism
This is the existence of two or more compounds with the same molecular formulae but different carbon chains that is the carbon are arranged differently e.g. C4H10
Chain isomers have the same chemical properties but different physical properties like melting point and boiling point due to stronger VAN DER WAALS properties in straight chain than in branch chain. This implies that they can be separated using their difference in physical properties.
- Functional group isomerism
They have the same molecular formulae but different functional group.
Functional group isomers belong to different homologous series because they have different functional group. It is commonly encountered in alcohols and ethers.
It can also be seen in aldehydes and ketones e.g. C3H6O
It can also exist in between carbonxylic acid and esthers. E.g. C3H6O
They have different physical and chemical properties and so can be distinguish by either using a physical or chemical test.
- Position isomerism
They have the same molecular formulae, same functional group but the functional group occupies different position on the carbon chain. Position isomers belong to the same homologous series e.g. C4H10O
- Metameric
It is the existence of two or more compounds with the same molecular formulae but different alkyl group, this type of isomerism is common in:
- Ether e.g. C4H10O
- Amines e.g.C3H9N
Metameric is similar to both chain and position isomerism because in ether for example, the length of principal carbon chain and the position of the functional group changes
- Tantomerism
It is a special type of functional group isomerism in which the two isomers are mutually inconvertible and formed a mixture which is in dynamic equilibrium. It also differs visually in the relative position of at least one atomic nucleus, generally hydrogen. There are several types of tantomerism of which keto-enol tantomerism is the most important. In this type, one form (tautomer) exists as a ketone while the other exists as enol.
