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.
- Constitutional or Structural Isomers
- Stereo/Configurational/Three dimensional/Space Isomers
