When neopentyl alcohol is heated with an acid , it slowly converted into an 85 : 15 mixture of alkenes A and B , respectively. What are these alkenes ?

Options

A.
B.
C.
D.

Answer

To determine the alkenes A and B formed from the dehydration of neopentyl alcohol when heated with sulfuric acid, we can follow these steps:

### Step-by-Step Solution:

1. **Identify Neopentyl Alcohol Structure**:
Neopentyl alcohol (2,2-dimethylpropan-1-ol) has the structure:
\[ \text{(CH}_3\text{)}_4\text{C(OH)CH}_2\text{ (or ) } \text{C(CH}_3\text{)}_4\text{CH}_2\text{OH} \]

2. **Reaction with Sulfuric Acid**:
When neopentyl alcohol is heated with sulfuric acid (H₂SO₄), the hydroxyl (-OH) group is protonated, making it a better leaving group. This leads to the formation of a carbocation.

3. **Formation of Carbocation**:
The protonation of the -OH group leads to the formation of a good leaving group (water), resulting in a carbocation. The most stable carbocation will form:
- The initial carbocation formed is a primary carbocation, but it can rearrange to form a more stable tertiary carbocation.

4. **Carbocation Rearrangement**:
The rearrangement occurs as follows:
- The methyl group from one of the neighboring carbon atoms can shift to stabilize the carbocation, leading to a tertiary carbocation.

5. **Elimination to Form Alkenes**:
From the tertiary carbocation, elimination can occur to form alkenes:
- If a hydrogen is removed from the adjacent carbon, two different alkenes can be formed:
- Alkene A (major product)
- Alkene B (minor product)

6. **Identify the Alkenes**:
- Alkene A (major product): 2,2-dimethylpropene (more substituted)
- Alkene B (minor product): 2-methylpropene (less substituted)

7. **Determine the Ratio**:
The problem states that the products are in an 85:15 ratio, which aligns with the expected stability of the alkenes formed:
- Alkene A (85%): 2,2-dimethylpropene
- Alkene B (15%): 2-methylpropene

### Final Answer:
- Alkene A: 2,2-dimethylpropene
- Alkene B: 2-methylpropene