tau·tom·er·ism 
(tô-tŏmə-rĭz′əm)
(tô-tŏmə-rĭz′əm)n.
Chemical isomerism characterized by facile interconversion of isomeric forms in equilibrium, especially by migration of a hydrogen atom.
[TAUTO- + (ISO)MERISM.]
tauto·mer (tôtə-mər) n.
tau′to·meric (tô′tə-mĕrĭk) adj.