Tautomerism is due to :-

Options

A. Delocalization of sigma electrons
B. Delocalization of pie electrons
C. Migration of active -H -atom
D. None is correct

Answer

**Step-by-step Solution:**

1. **Understanding Tautomerism**: Tautomerism is a chemical phenomenon where compounds exist in two or more interconvertible forms that differ in the position of protons and electrons. The most common type of tautomerism is keto-enol tautomerism.

2. **Example of Tautomerism**: Consider acetone (CH3COCH3). In this case, the keto form (acetone) can convert to the enol form through the migration of a hydrogen atom.

3. **Mechanism of Tautomerism**:
- The oxygen atom in the carbonyl group (C=O) has lone pairs of electrons.
- A hydrogen atom from a neighboring carbon can be abstracted by the oxygen, leading to the formation of a double bond between the carbon and oxygen.
- This process involves the movement of electrons and the migration of an active hydrogen atom.

4. **Conclusion**: Tautomerism is primarily due to the migration of active hydrogen atoms and the rearrangement of electrons, leading to different structural forms of the compound.

5. **Final Answer**: Tautomerism is due to the migration of active hydrogen.

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