Which of the following , upon treatment with tert-BuONa followed by addition of bromine water , fails to decolourise the colour of bromine ?

Options

A.
B.
C.
D.

Answer

To solve the question of which compound fails to decolorize bromine water upon treatment with tert-BuONa (sodium tert-butoxide) followed by bromine water, we will analyze each option step by step.

### Step-by-Step Solution:

1. **Understand the Reaction Conditions**:
- Sodium tert-butoxide (tert-BuONa) is a strong base that can abstract acidic hydrogens (protons) from beta positions of certain compounds.
- Bromine water is used to test for unsaturation (double or triple bonds) in organic compounds. Unsaturated compounds will decolorize bromine water.

2. **Identify the Nature of Each Compound**:
- We need to check if each compound has beta hydrogens that can be abstracted by tert-BuONa, leading to the formation of a double bond (alkene).

3. **Analyze Each Option**:
- **Option 1**: This compound has beta hydrogens. When treated with tert-BuONa, it will undergo elimination (E2 mechanism), forming a double bond. Therefore, it can decolorize bromine water.
- **Option 2**: Similar to option 1, this compound also has beta hydrogens. The reaction with tert-BuONa will also lead to the formation of a double bond, allowing it to decolorize bromine water.
- **Option 3**: This compound also has beta hydrogens. The same elimination reaction occurs, resulting in a double bond, thus decolorizing bromine water.
- **Option 4**: This compound lacks beta hydrogens (no beta carbon). Therefore, it cannot undergo elimination and will not form a double bond. Instead, it will undergo a substitution reaction, leading to a product that does not have unsaturation. As a result, this compound will not decolorize bromine water.

4. **Conclusion**:
- The compound that fails to decolorize bromine water is **Option 4** because it does not have any beta hydrogens to be abstracted, preventing the formation of a double bond.

### Final Answer:
**Option 4** fails to decolorize the color of bromine water.