Isomerism & Isomers

One of the special characteristics of organic compounds is “Isomerism”.

The word Isomerism comes from the Greek; where isos means “equal” and meros means “part”.

“Different compounds which have the same molecular formula but have different arrangements of atoms, that is, differ from each other in physical and chemical properties, are called Isomers (isomerides) and the phenomenon is known as Isomerism.”

They contain the same numbers of the same kinds of atoms, that is why the molecular weight is same, but the atoms are attached to one another in different ways. Isomers are different compounds because they have different molecular structures.

Example:

Acetone and Propylene oxide have the molecular formula C₃H₆O and therefore the same molecular weight. Yet acetone and propylene oxide have distinctly different boiling points and chemical reactivity that, as a result, lend them to distinctly different practical applications.

Acetone contains a double bond between the oxygen atom and the central carbon atom. Propylene oxide does not contain a double bond, but has three atoms joined in a ring. The connectivity of the atoms is clearly different in acetone and propylene oxide. Their structures have the same molecular formula but a different constitution. it is an example of Isomerism.

Types of Isomerism

There are two major kinds of isomers.

1.  Constitutional or Structural Isomers
2. Stereo/Configurational/Three dimensional/Space Isomers