For which of the following compound tautomerization reaction is very slow?

Options

A.
B.
C.
D.

Answer

To determine which compound has a very slow tautomerization reaction, we need to analyze the stability of the enol form compared to the keto form for each compound. Tautomerization refers to the equilibrium between the keto form (a carbonyl compound) and the enol form (an alcohol with a double bond).

### Step-by-Step Solution:

1. **Understanding Tautomerization**:
- Tautomerization is the process where a compound can exist in two forms: the keto form (C=O) and the enol form (C=C-OH). The reaction involves the transfer of a hydrogen atom and a shift of a double bond.

2. **Analyzing Each Compound**:
- **Compound A**: C=C(CF2)OH
- The presence of two fluorine atoms (CF2) creates a strong electron-withdrawing effect (−I effect), which stabilizes the negative charge on the enol form. This stabilization makes it less likely for the enol to convert to the keto form, resulting in a slower tautomerization.

- **Compound B**: C=C(CH2)OH
- This compound does not have strong electron-withdrawing groups. The enol form is less stabilized compared to Compound A, making the tautomerization faster.

- **Compound C**: Cyclic enol compound
- Similar to Compound B, this compound lacks strong stabilizing groups. The tautomerization is expected to occur at a moderate rate.

- **Compound D**: Another enol form
- Like Compounds B and C, this compound also lacks significant stabilization for the enol form, leading to a faster tautomerization.

3. **Conclusion**:
- Among the compounds analyzed, **Compound A** (C=C(CF2)OH) exhibits the slowest tautomerization due to the stabilizing effect of the electron-withdrawing fluorine atoms, which makes the enol form more stable and less likely to convert to the keto form.

### Final Answer:
- **The compound for which the tautomerization reaction is very slow is Compound A (C=C(CF2)OH).**