https://doi.org/10.1351/goldbook.T06396
The identity reaction leading to exchange of the positions of identical ligands. The indistinguishable molecular entities involved are called topomers. For example in the reaction below the two identical ligating atoms Na and Nb are interchanged by rotation about the C-aryl bond but may be identified by NMR spectroscopy. This is a degenerate isomerization. 