What is the order of reactivity of these alkenes
`(CH_(3))_(2)C=CH_(2)(I), CH_(3)CH=CH_(2)(II)` and `CH_(2)=CH_(2)(III)` when subjected to acid - catalysed hydration?

Options

A. `I gt II gt III`
B. `I gt III gt II`
C. `III gt II gt I`
D. `II gt I gt III`

Answer

To determine the order of reactivity of the given alkenes when subjected to acid-catalyzed hydration, we will analyze the stability of the carbocation intermediates formed during the reaction. The three alkenes provided are:

1. (CH₃)₂C=CH₂ (I)
2. CH₃CH=CH₂ (II)
3. CH₂=CH₂ (III)

### Step 1: Understand the Mechanism of Acid-Catalyzed Hydration
In acid-catalyzed hydration, the alkene first undergoes protonation to form a carbocation. The stability of this carbocation will determine the reactivity of the alkene.

### Step 2: Identify the Carbocation Formed from Each Alkene
- **For Alkene I: (CH₃)₂C=CH₂**
- Protonation leads to the formation of a tertiary carbocation: (CH₃)₂C⁺-CH₃.
- Tertiary carbocations are highly stable due to hyperconjugation and inductive effects from the surrounding alkyl groups.

- **For Alkene II: CH₃CH=CH₂**
- Protonation leads to the formation of a secondary carbocation: CH₃-CH⁺-CH₃.
- Secondary carbocations are less stable than tertiary but more stable than primary carbocations.

- **For Alkene III: CH₂=CH₂**
- Protonation leads to the formation of a primary carbocation: CH₃-CH₂⁺.
- Primary carbocations are the least stable due to the lack of alkyl groups to stabilize the positive charge.

### Step 3: Compare the Stability of the Carbocations
- Tertiary carbocation (from I) > Secondary carbocation (from II) > Primary carbocation (from III)
- Therefore, the stability order is:
- (I) > (II) > (III)

### Step 4: Determine the Order of Reactivity
Since the reactivity of the alkenes in acid-catalyzed hydration is directly related to the stability of the carbocations formed, we can conclude the order of reactivity:
- Alkene I is the most reactive, followed by Alkene II, and finally Alkene III.

### Final Order of Reactivity
The order of reactivity of the alkenes when subjected to acid-catalyzed hydration is:
**I > II > III**