Constitutional Isomers
These isomers differ in the arrangement of atoms. There are five types of constitutional isomers.
Chain Isomers
Consider the molecular formula, C₅H₁₂. The possible structures are,
The longest chain of carbon is also called the parent chain. In the three isomers, number of atoms in the parent chain are different.
So, the isomers which have different number of carbon atoms in the parent chain are chain isomers.
Functional Group Isomers
The following are a few functional groups
As the name suggests, these have the same molecular formula but have different functional groups. Some examples of functional group isomers are
Position Isomers
These isomers possess the same number of atoms in the parent chain and the same functional group, however, the position of the functional group is different.
In the above example, the alcohol group is in the second and the first position respectively.
Tautomers
These isomers are formed due to the movement of electrons. The most commonly found tautomer pair is the keto enol.
In a carbonyl compound, the alpha carbon is attached to the carbonyl carbon. The alpha hydrogen is attached to the alpha carbon. In carbonyl compounds, alpha hydrogen is slightly acidic.
In basic condition, the base removes the slightly acidic alpha hydrogen. This hydrogen is then transferred to the oxygen of the carbonyl group leading to the formation of an enol.
Metamers
This kind of isomerism is shown by only a few kinds of functional groups. The following are a few examples
The R represents the alkyl group. In these isomers, the alkyl groups on either sides of the functional group are different. It is easier to understand with an example. Ether, for example
The first molecule has a methyl and propyl group on either side of the oxygen. In case of the second molecule ethyl groups are on either side of the oxygen.
In case of secondary amine,
Note- Metamers should not be confused with position isomers. The below example is position isomers because the alkene is in the first and second position respectively.Metamers exist in the presence of a heteroatom.in the carbon chain.
