A particularly interesting type of constitutional isomerism is linkage isomerism, which is possible when one or more of the ligands in a complex can bind through either of 2 donor atoms. Such ligands are called ambidentate to emphasize this ability. Generally, IR spectroscopy is the best way to distinguish linkage isomers. Stereoisomers are compounds that have the same empirical formula and the same atom attachments, but different spatial orientation of the atoms. We recognize two categories of stereoisomerism.
Enantiomers are molecules having non-superimposable mirror images.
Enantiomers are identical in all physical properties except the direction in which they rotate plane polarized light. Molecules that can exist in enantiomeric forms are said to be chiral , which is the Greek word denoting handedness. In general, a molecule is chiral if it has neither a plane of symmetry nor a center of symmetry . We will deal with enantiomers after we have discussed symmetry. Stereoisomers that are not enantiomers are diastereomers.