Isomers are compounds with the same chemical composition but with different structures. There are two categories: structural isomers and stereoisomers. Structural isomerism is exemplified by the molecules (ethylmethylether) and (1- and 2-propanol). Examples of stereoisomerism are the cis and trans modifications of specific groups of atoms within a molecule, for example (1,2-dichloroethene). Another type known as enantiomers are two stereoisomers that are mirror images of each other, which occurs in different forms of (glucose).