Dehydration of 1-butanol gives 2-butane as a major product, by which of the following intermediate the compound 2-butene obtained.

Options

A.
B.
C.
D.

Explanation

To solve the question regarding the dehydration of 1-butanol to form 2-butene and identify the intermediate involved, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Structure of 1-Butanol**:
The molecular structure of 1-butanol (butan-1-ol) is:
\[ CH_3-CH_2-CH_2-CH_2OH \]
Here, the hydroxyl (-OH) group is attached to the first carbon.

**Hint**: Remember that 1-butanol has a four-carbon chain with the -OH group on the first carbon.

2. **Dehydration Reaction**:
The dehydration of 1-butanol involves the removal of a water molecule (H2O). This reaction is typically facilitated by a dehydrating agent, such as concentrated sulfuric acid (H2SO4), which generates protons (H+).

**Hint**: Concentrated sulfuric acid acts as a catalyst and helps in protonating the alcohol group.

3. **Formation of Oxonium Ion**:
The alcohol group (-OH) is protonated to form an oxonium ion:
\[ CH_3-CH_2-CH_2-CH_2OH_2^+ \]
This oxonium ion is unstable and leads to the elimination of water.

**Hint**: The oxonium ion is formed when the -OH group is protonated, making it a better leaving group.

4. **Formation of Carbocation**:
Upon the elimination of water, a carbocation is formed. In this case, the initial carbocation formed is a primary carbocation:
\[ CH_3-CH_2-CH_2-CH_2^+ \]

**Hint**: Primary carbocations are less stable and may undergo rearrangement to form more stable carbocations.

5. **Carbocation Rearrangement**:
The primary carbocation undergoes a 1,2-hydride shift to form a more stable secondary carbocation:
\[ CH_3-CH^+-CH_2-CH_3 \]
Here, the positive charge has shifted to the second carbon, creating a secondary carbocation.

**Hint**: Carbocation rearrangement occurs to achieve greater stability; secondary carbocations are more stable than primary ones.

6. **Formation of 2-Butene**:
The secondary carbocation can lose a proton (H+) to form 2-butene. According to Zaitsev's rule, the more substituted alkene is favored:
\[ CH_3-CH=CH-CH_3 \]

**Hint**: Zaitsev's rule states that the more substituted alkene is the major product in elimination reactions.

7. **Identify the Intermediate**:
The intermediate that leads to the formation of 2-butene is the secondary carbocation formed after the rearrangement.

**Final Answer**: The intermediate involved in the dehydration of 1-butanol to form 2-butene is the **secondary carbocation**.