Which of the following show stable or major form of tautomerism?

Options

A.
B.
C.
D.

Explanation

To determine which of the given compounds exhibit stable or major forms of tautomerism, we will analyze each compound step by step.

### Step 1: Analyze Compound A
- **Structure**: Compound A does not have any alpha hydrogen atoms.
- **Conclusion**: Tautomerism requires the presence of alpha hydrogen atoms for the hydrogen to shift and form a new isomer. Since there are no alpha hydrogens, tautomerism is not possible for Compound A.

### Step 2: Analyze Compound B
- **Structure**: Compound B has alpha hydrogen atoms.
- **Tautomerism Process**: The double bond will shift, and the alpha hydrogen will move to the oxygen atom, resulting in the formation of an alcohol.
- **Conclusion**: The resulting compound is stable, indicating that tautomerism occurs here and is a major form.

### Step 3: Analyze Compound C
- **Structure**: Compound C also has alpha hydrogen atoms.
- **Tautomerism Process**: Similar to Compound B, the double bond shifts, and the alpha hydrogen moves to the oxygen.
- **Stability Check**: However, the resulting compound does not follow Hückel's rule (4n + 2) and is classified as anti-aromatic, making it unstable.
- **Conclusion**: Although tautomerism occurs, it leads to an unstable product.

### Step 4: Analyze Compound D
- **Structure**: Compound D has multiple double bonds and alpha hydrogen atoms.
- **Tautomerism Process**: The double bonds shift, and the hydrogen atoms move to the oxygen, resulting in a structure with a negative charge and an OH group.
- **Stability Check**: The resulting compound exhibits extended conjugation, which is stable.
- **Conclusion**: Tautomerism occurs here and is stable.

### Final Conclusion
- The compounds that show stable or major forms of tautomerism are **Compound B** and **Compound D**.

### Summary of Results
- **Stable Tautomerism**:
- Compound B
- Compound D
- **Unstable Tautomerism**:
- Compound A (no tautomerism)
- Compound C (unstable due to anti-aromaticity)