A given molecular formula can correspond to a number of different compounds.
Isomerism can happen to the carbon chain, to the chemical function or to both at the same time.
The more atoms in the molecular formula, the larger the possibility of isomerism.
For instance, the molecular formula C20H42 corresponds to more than 200.000 different compounds, believe it or not...
An important property of single bonds is that they can be twisted over themselves, giving rise to structures with different spatial arrangement of its atoms. This kind of subtle isomers are called ROTAMERS or CONFORMERS.
Obviously, they interconvert by the rotation of single bonds.
The isomers that bear the same bond pattern but don't interconevert by the rotation of single bonds are named after CONFIGURATIONAL ISOMERS.
Those not having the relationship of object and non-superimposable mirror image are denoted as DIASTEREISOMERS.
The CONFIGURATIONAL ISOMERS being object and non-superimposable mirror image are named ENANTIOMERS.