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ISOMERISM
Isomerism is the phenomenon in which more than one compounds have the same chemical formula but different chemical structures. Chemical compounds that have identical chemical formula but differ in properties and the arrangement of atoms in the molecule are called isomers. Therefore, the compounds that exhibit isomerism are known as isomers. The word “isomer” is derived from the Greek words “isos” and “meros”, which mean “equal parts”. This term was coined by the Swedish chemist Jacob Berzelius in the year 1830.
Types
There are two primary types of isomerism, which can be further categorized into different subtypes. These primary types are Structural Isomerism and Stereoisomerism. The classification of different types of isomers is illustrated below.
1. Chain Isomerism:
It is also known as skeletal isomerism. The components of these isomers display differently branched structures. Commonly, chain isomers differ in the branching of carbon. An example of chain isomerism can be observed in the compound C 5 H 12 , as illustrated below.
2. Position Isomerism
The positions of the functional groups or substituent atoms are different in position isomers. Typically, this isomerism involves the attachment of the functional groups to different carbon atoms in the carbon chain. An example of this type of isomerism can be observed in the compounds having the formula C 3 H 7 Cl.
4. Metamerism
This type of isomerism arises due to the presence of different alkyl chains on each side of the functional group. It is a rare type of isomerism and is generally limited to molecules that contain a divalent atom (such as sulfur or oxygen), surrounded by alkyl groups. Example: C 4 H 10 O can be represented as : ethoxyethane (C 2 H 5 OC 2 H 5 ) and methoxy-propane (CH 3 OC 3 H 7 ).
5. Tautomerism
Tautomerism is a dynamic equilibrium between two compounds with same molecular formula. A tautomer of a compound refers to the isomer of the compound which only differs in the position of protons and electrons. Typically, the tautomers of a compound exist together in equilibrium and easily interchange. It occurs via an intramolecular proton transfer. The most common form of tautomerism is keto-enol tautomerism. A carbonyl compound containing at least one α-hydrogen atom is converted to an enol by the transfer of an α-hydrogen onto the oxygen atom. For example,
