Structural isomers are compounds with the same molecular formula but different structural formulae. They can be :1. Carbon chain isomers that differ in the length of the carbon chain2. Positional isomers that have the same functional group, but in different positions on the carbon skeleton3. Functional group isomers that are members of different homologous series and hence have different functional groups, e.g. methoxymethane and ethanolStereoisomers have the same structural formula, but the atoms in these compounds have differing spatial arrangements. There are two types of stereoisomerism :1. Geometric isomerism is caused by the presence of a functional group that restricts rotation. It is also called cis-/trans- isomerism or E/Z isomerism.2. Optical isomers/ enantiomers are non-superimposable mirror images of each other meaning that they exist as right- and left- handed structures.