Which of the following alcohol on dehydration with conc `H_(2)SO_(4)` gives but-2- ene?

Options

A. 2-methylpropan-2-ol
B. Butan-1-ol
C. 2-methyl propan-1-ol
D. Butan-2-ol

Answer

To determine which alcohols, when dehydrated with concentrated H₂SO₄, yield but-2-ene, we need to analyze the structure of the alcohols provided and the dehydration reaction mechanism.

### Step-by-Step Solution:

1. **Identify the Alcohols**:
We need to consider the structures of the alcohols given in the options. The relevant alcohols are:
- 2-methylpropan-2-ol
- 2-methylpropan-1-ol
- Butan-1-ol
- Butan-2-ol

2. **Understand Dehydration Reaction**:
Dehydration of alcohols involves the removal of a water molecule (H₂O) in the presence of an acid (in this case, concentrated H₂SO₄). This typically leads to the formation of a carbocation intermediate.

3. **Analyze Each Alcohol**:
- **2-methylpropan-2-ol**:
- This is a tertiary alcohol. Upon dehydration, it forms a tertiary carbocation. The rearrangement leads to the formation of 2-methylpropene (not but-2-ene).
- **2-methylpropan-1-ol**:
- This is a primary alcohol. Dehydration leads to a less stable primary carbocation, which does not favor the formation of but-2-ene.
- **Butan-1-ol**:
- This is a primary alcohol. Dehydration forms a primary carbocation, which rearranges to a more stable secondary carbocation. This can lead to the formation of but-2-ene.
- **Butan-2-ol**:
- This is a secondary alcohol. Dehydration leads to a secondary carbocation, which can also rearrange to form but-2-ene directly.

4. **Conclusion**:
The alcohols that can yield but-2-ene upon dehydration with concentrated H₂SO₄ are:
- Butan-1-ol
- Butan-2-ol

### Final Answer:
Both Butan-1-ol and Butan-2-ol can give but-2-ene upon dehydration with concentrated H₂SO₄.

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