Chain Isomerism
Molecules with the same molecular formula but different carbon chains e.g. hexane and 2-methylpentane
Position Isomerism
Molecules with the same molecular formula but the functional group in different positions e.g.hexan-1-ol and hexan-2-ol
Functional Group Isomerism
Molecules with the same molecular formula but with different functional groups e.g. propanal and propanone
Note:Alcohols and ethers, aldehydes and ketones, alkenes and cycloalkanes and carboxylic acids and esters are functional isomers of each other.