Place the following alcohols in decreasing order of rate of dehydration with concentration `H_2SO_4`.
1. `CH_3CH_2CH(OH)CH_2CH_2CH_3`
2. `(CH_3)_2C(OH)CH_2CH_2CH_3`
3. `(CH_3)_2C(OH)CH(CH_3)_2`
4. `CH_3CH_2CH(OH)CH(CH_3)_2`
5. `CH_3CH_2CH_2CH_2CH_2CH_2OH`

Options

A. `3 gt 2 gt 4 gt 5 gt 1 `
B. `3 gt 2 gt 4 gt 1 gt 5`
C. `3 gt 2 gt 1 gt 4 gt 5`
D. `3 gt 2 gt 1 gt 5 gt 4`

Answer

To determine the decreasing order of the rate of dehydration of the given alcohols with concentrated H₂SO₄, we need to analyze the stability of the carbocations formed during the dehydration process. The stability of carbocations is crucial because the rate of dehydration depends on how quickly these carbocations can form.

### Step-by-Step Solution:

1. **Identify the Alcohols and Their Structures**:
- 1. `CH₃CH₂CH(OH)CH₂CH₂CH₃` (1-hexanol)
- 2. `(CH₃)₂C(OH)CH₂CH₂CH₃` (2-pentanol)
- 3. `(CH₃)₂C(OH)CH(CH₃)₂` (2-methyl-2-pentanol)
- 4. `CH₃CH₂CH(OH)CH(CH₃)₂` (3-pentanol)
- 5. `CH₃CH₂CH₂CH₂CH₂CH₂OH` (1-hexanol)

2. **Determine the Type of Carbocation Formed**:
- For each alcohol, we need to consider the type of carbocation formed after dehydration:
- **1**: Forms a secondary carbocation.
- **2**: Forms a tertiary carbocation.
- **3**: Forms a tertiary carbocation (more steric hindrance).
- **4**: Forms a secondary carbocation.
- **5**: Forms a primary carbocation.

3. **Rank the Carbocation Stability**:
- Tertiary (3°) > Secondary (2°) > Primary (1°)
- Therefore, the stability ranking based on the carbocation formed is:
- 3° (from 2 and 3) > 2° (from 1 and 4) > 1° (from 5)

4. **Consider Steric Hindrance**:
- Between the tertiary carbocations (2 and 3), the one with more steric hindrance (3) will be slightly less stable than the one with less hindrance (2).
- Between the secondary carbocations (1 and 4), the one with more substituents (4) will be more stable than the one with fewer (1).

5. **Final Order of Dehydration Rate**:
- Based on the stability of the carbocations:
- 3 (most stable, tertiary) > 2 (tertiary) > 4 (secondary, more stable) > 1 (secondary, less stable) > 5 (primary)
- Therefore, the order of decreasing rate of dehydration is:
- (3) > (2) > (4) > (1) > (5)

### Final Answer:
The decreasing order of the rate of dehydration with concentrated H₂SO₄ is:
**3 > 2 > 4 > 1 > 5**