Which of the following compounds give most stable carbonium ion on dehydration?

Options

A. `CH_(3)-underset(CH_(3))underset(|)overset(CH_(3))overset(|)(C)-OH`
B. `CH_(3)-underset(CH_(3))underset(|)(CH)-CH_(2)OH`
C. `CH_(3)-underset(OH)underset(|)(CH)-CH_(2)-CH_(3)`
D. `CH_(3)CH_(2)CH_(2)CH_(2)OH`

Answer

To determine which compound gives the most stable carbonium ion upon dehydration, we can follow these steps:

### Step 1: Understand the concept of carbonium ions
Carbonium ions (or carbocations) are positively charged carbon species. Their stability is influenced by the degree of substitution. The order of stability is:
- Tertiary (3°) > Secondary (2°) > Primary (1°) > Methyl (0°)

### Step 2: Identify the compounds in question
Let's consider the dehydration of 1-butanol (C4H10O) as an example. When 1-butanol undergoes dehydration, it loses a water molecule (H2O) to form a carbocation.

### Step 3: Draw the structure of 1-butanol
1-butanol can be represented as:
```
CH3-CH2-CH2-CH2-OH
```

### Step 4: Dehydrate 1-butanol
During dehydration, the hydroxyl group (OH) is removed along with a hydrogen atom from an adjacent carbon, leading to the formation of a double bond and a carbocation. The reaction can be represented as:
```
CH3-CH2-CH2-CH2-OH → CH3-CH2-CH=CH2 + H2O
```
This results in a primary carbocation, which is less stable.

### Step 5: Consider carbocation rearrangement
Primary carbocations can rearrange to form more stable secondary or tertiary carbocations. In the case of 1-butanol, a hydride shift can occur:
```
CH3-CH2-CH2-CH2+ → CH3-CH2-CH+-CH3 (2° carbocation)
```
This rearrangement leads to a more stable secondary carbocation.

### Step 6: Compare the stability of possible carbocations
Now, we can compare the stability of the carbocations formed:
- The primary carbocation formed directly from 1-butanol is less stable.
- The secondary carbocation formed after rearrangement is more stable.

### Step 7: Determine the final product
The final product of the dehydration of 1-butanol, after rearrangement, is 2-butene, which is more stable due to the more substituted double bond.

### Conclusion
Thus, when considering the dehydration of 1-butanol, the most stable carbonium ion formed is the secondary carbocation after rearrangement.