tautomeric

Tautomeric refers to tautomerism, a form of structural isomerism in which compounds exist in two or more interconvertible forms called tautomers. These forms share the same molecular formula but differ in the position of a proton and a double bond, and they rapidly interconvert under given conditions.

The most familiar example is keto–enol tautomerism, where a carbonyl-containing compound can rearrange to an alcohol with a relocated double bond. Other common types include thione–thiol tautomerism, imine–enamine tautomerism, and ring tautomerism such as lactam–lactim forms in heterocycles. Tautomers interconvert via intramolecular or catalyzed proton transfers and may be in dynamic equilibrium that depends on the surrounding environment.

The tautomeric state of a molecule is influenced by solvent, temperature, pH, and catalysts. Under physiological conditions, one form is often favored, but small fractions of alternative tautomers can persist and affect chemical behavior. This dynamic equilibrium can impact acidity and basicity, regioselectivity in reactions, and spectroscopic properties such as infrared and nuclear magnetic resonance spectra. In medicinal chemistry, tautomeric equilibria can influence binding to biological targets, pharmacokinetics, and metabolism. In biology, rare tautomeric forms of nucleobases can contribute to mispairing during replication.

Examples include acetylacetone, which exhibits keto–enol tautomerism, and nucleobases that can access rare tautomeric forms under certain conditions. Understanding tautomeric behavior is important for predicting reactivity, designing materials, and interpreting spectroscopic data.