Introduction: Isomers are compounds which have the same molecular formula, but differ in the way the atoms are arranged. There are three types of isomers – constitutional, configurational, and conformational. Constitutional isomers are isomers where the atoms are linked together in a different skeletal framework and are different compounds. Configurational isomers are structures having the same atoms and bonds, but which have different geometrical shapes which cannot be interconverted without breaking covalent bonds. Configurational isomers can be separated and are different compounds with different properties. Conformational isomers are different shapes of the same molecule and cannot be separated.
Constitutional isomers are compounds which have the same molecular formula but have the atoms joined together in a different way. Constitutional isomers have different physical and chemical properties. Example:
Alkanes of a particular molecular formula can have various constitutional isomers. The larger the alkane, the more isomers which are possible. Alkanes of a particular molecular formula can exist as different constitutional isomers. For example, the alkane having the molecular formula C4H10 can exist as two constitutional isomers – the straight chain alkane (butane) or the branched alkane (2-methylpropane; Fig. 1). These are different compounds with different physical and chemical properties.