In chemistry, conformational isomerism is a form of stereoisomerism in which the isomers can be interconverted exclusively by rotations about formally single bonds. Such isomers are generally referred to as conformational isomers or conformers and specifically as rotamers when the rotation leading to different conformations is restricted (hindered) rotation, in the sense that there exists a rotational energy barrier that needs to be overcome to convert one conformer to another. Conformational isomers are thus distinct from the other classes of stereoisomers for which interconversion necessarily involves breaking and reforming of chemical bonds. The rotational barrier, or barrier to rotation, is the activation energy required to interconvert rotamers.
Read more about Conformational Isomerism: Types of Conformational Isomerism, Equilibrium Population of Conformers, Isolation or Observation of The Conformational Isomers, Techniques For Study of Conformational Isomerism, Conformation-dependent Reactions, Protein Rotamer Libraries