Structural Isomer - Position Isomerism

In position isomerism a functional group or other substituent changes position on a parent structure. In the table below, the hydroxyl group can occupy three different positions on an n-pentane chain forming three different compounds.

Many aromatic isomers exist because substituents can be positioned on different parts of the benzene ring. Only one isomer of phenol or hydroxybenzene exists but cresol or methylphenol has three isomers where the additional methyl group can be placed on three different positions on the ring. Xylenol has one hydroxyl group and two methyl groups and a total of 6 isomers exist.