Isomerism

• Isomerism is a consequence of the directional nature of the covalent bond.
• This results in atoms arranged in different positions are spatial arrangements leading to isomers.
• Isomers are compounds, which have the same molecular formula but different structure or spatial arrangement (configuration).

Classification:

Structural Isomersim (Constitutional isomerism):

Functional isomers have the same molecular formula but different functional group. Both H₃C-O-CH₃ and CH₃CH₂OH have the smae moleuclar formula C₂H₆O but different functional group, one is an ether and the other is an alcohol. Similarly acetone and propanaldehyde (CH₃COCH₃ and CH₃CH₂CHO) are a pair of functional isomers.

Positional isomers have the same molecular formula but differ in the position of attachment of the functional group or substitutent. 1-Chloropropane and 2-Chloroproane (CH₃CH₂CH₂Cl and CH₃CHClCH₃ ) are a pair of positional isomers so are 2-Butene and 1-Butene.

Chain isomers have the same molecular formula but different chain length. Pentane and 2-Methyl butane is such a pair, the former has five carbon atoms in a single chain while the later has four cabons in a single chain and the fifth is attached as a branch.