Meaning of tautomerism

tau•tom•er•ism

Pronunciation: (tô-tom'u-riz"um), [key]
— n. Chem.
  1. the ability of certain organic compounds to react in isomeric structures that differ from each other in the position of a hydrogen atom and a double bond.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.