Arrange reactivity of given compounds in decreasing order for electrophilic addition reaction
`{:(1.C_(6)H_(5)-CH=CH_(2)" "2.C_(6)H_(5)-underset(CH_(3))underset("| ")"C "=CH-CH_(3)),(3.C_(6)H_(5)-underset(C_(6)H_(5))underset("| ")"C "=CH-CH_(3)" "4.CH_(2)=CH-NO_(2)):}`
Select the correct answer from codes given below

Options

A. 4, 1, 2, 3
B. 3, 2, 1, 4
C. 2, 3, 1, 4
D. 2, 3, 4, 1

Answer

To arrange the given compounds in decreasing order of their reactivity for electrophilic addition reactions, we need to analyze the stability of the carbocation intermediates formed during these reactions. The stability of carbocations is influenced by the number of alkyl groups attached to the positively charged carbon and the presence of resonance effects.

### Step-by-Step Solution:

1. **Identify the Compounds**:
- Compound 1: \( C_6H_5-CH=CH_2 \)
- Compound 2: \( C_6H_5-CH(CH_3)-CH=CH_3 \)
- Compound 3: \( C_6H_5-C(C_6H_5)=CH-CH_3 \)
- Compound 4: \( CH_2=CH-NO_2 \)

2. **Electrophilic Addition Mechanism**:
- In electrophilic addition reactions, an electrophile (like H⁺ from HCl) adds to the double bond, forming a carbocation intermediate. The stability of this carbocation determines the reactivity of the compound.

3. **Analyze Each Compound**:
- **Compound 1**: When H⁺ adds, it forms a secondary carbocation \( C_6H_5-CH^+-CH_3 \). This carbocation is stabilized by resonance with the phenyl ring.
- **Compound 2**: The addition of H⁺ leads to the formation of a tertiary carbocation \( C_6H_5-CH^+(CH_3)-CH_2-CH_3 \). Tertiary carbocations are more stable due to hyperconjugation and resonance.
- **Compound 3**: This compound also forms a tertiary carbocation \( C_6H_5-C^+(C_6H_5)-CH_2-CH_3 \). The presence of two phenyl groups provides significant resonance stabilization.
- **Compound 4**: The addition of H⁺ results in a primary carbocation \( CH_2^+-CH-NO_2 \). The nitro group (NO₂) is an electron-withdrawing group, which destabilizes the carbocation.

4. **Rank the Carbocation Stability**:
- **Most Stable**: Compound 3 (tertiary with strong resonance)
- **Second Stable**: Compound 2 (tertiary with resonance)
- **Third Stable**: Compound 1 (secondary with resonance)
- **Least Stable**: Compound 4 (primary with destabilizing group)

5. **Order of Reactivity**:
- Since reactivity in electrophilic addition reactions follows the stability of the carbocation:
- **Reactivity Order**: Compound 3 > Compound 2 > Compound 1 > Compound 4

6. **Final Arrangement**:
- Thus, the decreasing order of reactivity for electrophilic addition reactions is:
- **3 > 2 > 1 > 4**