Three categories of constitutional isomers are skeletal, positional, and functional isomers.
|Example of skeletal isomerism|
In position isomerism a functional group changes position on the chain. In the diagram, pentan-2-ol has become pentan-3-ol. 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.
In functional group isomerism a functional group splits up and becomes a different group. Here is an example of functional group isomerism: take cyclohexane, C6H12 and hex-1-ene, also C6H12. These two are considered functional group isomers because cyclohexane is an alkane and hex-1-ene is an alkene. Both must have the same molecular formula.
DIETHYL ETHER CH3-CH2-O-CH2-CH3