Tautomerism: Features, Types, Factors and Mechanism (56 mins) | Lecture 108/210 | BITSAT (Birla Institute of Technology & Science Admission Test) Chemistry

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Principles of Organic ChemistryShapes of Simple MoleculesIsomerism

• Tautomerism is a form of isomerism where compounds can interconvert between two (or more) structural forms, typically involving the relocation of a proton (H⁺ ) and a shift in the position of a double bond.
• The different forms are called tautomers, and the process of interconversion is known as tautomerization.

Key Features

• Dynamic Equilibrium: Tautomers exist in a dynamic equilibrium, meaning they can rapidly interconvert.
• Proton Shift: The interconversion usually involves the migration of a hydrogen atom (proton) along with a shift in the position of a double bond.
• Functional Group Change: The functional groups of the molecule change during tautomerization (e. g. , keto to enol).

Types of Tautomerism

• Keto-Enol Tautomerism:
• Lactam-Lactim Tautomerism:
• Amide-Imidic Acid Tautomerism:
• Nitro-Aci-Nitro Tautomerism:

Conditions for Tautomerism

• Presence of an Acidic Proton: A hydrogen atom (proton) must be present on a carbon adjacent to a functional group (e. g. , carbonyl group).
• Presence of a Double Bond: The molecule must have a double bond that can shift during tautomerization.
• Catalysts: Tautomerization can be catalyzed by acids, bases, or enzymes.

Factors Affecting Tautomerism

• Temperature: Higher temperatures generally favor the enol form due to increased kinetic energy.
• Solvent: The nature of the solvent can influence the equilibrium position. Polar solvents often stabilize the keto form.
• Substituents: Electron-withdrawing or electron-donating groups can affect the stability of the tautomers.