Maximum -I effect is exerted by the group

Options

A. `-C_(6)H_(5)`
B. `-OCH_(3)`
C. `-Cl`
D. `-NO_(2)`

Answer

To determine which group exerts the maximum -I (negative inductive) effect, we need to analyze the electronegativity of different groups and their ability to withdraw electron density from a carbon chain. Here’s a step-by-step solution:

### Step 1: Understand the -I Effect
The -I effect refers to the electron-withdrawing ability of a substituent attached to a carbon chain. Electronegative atoms or groups pull electron density towards themselves, creating a polarization in the sigma bond.

**Hint:** Remember that the -I effect is stronger for more electronegative atoms.

### Step 2: Identify the Groups Given
The groups mentioned in the question are:
- Phenyl group (C6H5)
- Methoxy group (OCH3)
- Chlorine (Cl)
- Nitro group (NO2)

**Hint:** List the groups and their electronegativities to compare their -I effects.

### Step 3: Analyze the Electronegativity of Each Group
- **Nitro group (NO2)**: Contains nitrogen, which is highly electronegative and has a strong -I effect.
- **Chlorine (Cl)**: Also electronegative, but less than nitrogen in the nitro group.
- **Methoxy group (OCH3)**: The oxygen is electronegative, but the methoxy group has a +R effect (resonance effect) which can counteract its -I effect.
- **Phenyl group (C6H5)**: Has a weak -I effect due to resonance stabilization.

**Hint:** Compare the electronegativities of nitrogen, chlorine, oxygen, and carbon to determine the strongest -I effect.

### Step 4: Order the Groups Based on Their -I Effect
Based on the electronegativities and the nature of the groups, we can rank them:
1. **Nitro group (NO2)** - Maximum -I effect
2. **Chlorine (Cl)** - Moderate -I effect
3. **Methoxy group (OCH3)** - Weak -I effect due to +R effect
4. **Phenyl group (C6H5)** - Least -I effect

**Hint:** Use the electronegativity values to justify the order.

### Step 5: Conclusion
The group that exerts the maximum -I effect is the **Nitro group (NO2)**.

**Final Answer:** D) Nitro group (NO2)