Definitions: Conformational Isomers
Conformational isomers are stereoisomers that can be converted into one another by rotation around a single bond.
(Note: Conformational isomers are normally best seen using Newman Projections, so this structural representation will be used in this section of the tutorial. If you are not familiar with Newman Projections, click here to learn about them.)
For example, eclipsed, gauche, and anti butane are all conformational isomers of one another. (Recall that eclipsed means that identical groups are all directly in-line with one another, gauche means that identical groups are 60 degrees from one another, and anti means that identical groups are 180 degrees from one another.)
These molecules can be interconverted by rotating around the central carbon single bond. For example, eclipsed butane can be made into gauche butane by rotating 60 degrees and into anti butane by rotating 180 degrees. Similarly, gauche butane can be made into anti butane by rotating 120 degrees. This rotation can be seen in the animation below. Because of this rotational property, eclipsed, gauche, and anti butane are conformational isomers
of one another.