Definition of tautomer in US English:



  • Each of two or more isomers of a compound which exist together in equilibrium, and are readily interchanged by migration of an atom or group within the molecule.

    • ‘In our previous study on vibrational relaxation in HRP the relaxation time varied in the range of 1-10 ps for different vibrational modes of pyrrole tautomers of the chromophore.’
    • ‘Most often, the ketone is the much more stable of the two tautomers.’
    • ‘These structures are called tautomers, which exist in dynamic equilibrium with each other.’
    • ‘Earlier studies also support the fact that phenolic compounds could convert to different tautomers, quinone, ketone and dimers at higher pH in the presence of oxidative species.’
    • ‘Because the interconversion of the two tautomers is slower than the actual proton transfer reaction, a conformational change is probably associated with the isomerization.’


Early 20th century: blend of tauto- ‘same’ and isomer.