At conjugated position -NO imparts

Options

A. `+M` and + I effect
B. `-M` and -I effect
C. `+M` and -I effect
D. `-M` and +I effect

Answer

To solve the question "At conjugated position -NO imparts," we need to analyze the effects of the nitro group (-NO) when it is attached to a conjugated system. Here’s a step-by-step explanation:

### Step 1: Understanding the Structure
- A conjugated system consists of alternating double and single bonds, which allows for the delocalization of electrons.
- The -NO group can be represented as -N=O, where nitrogen is bonded to oxygen with a double bond.

**Hint:** Remember that conjugated systems allow for the movement of electrons, which is crucial for understanding the effects of substituents.

### Step 2: Electronegativity Consideration
- In the -NO group, oxygen is more electronegative than nitrogen, and nitrogen is more electronegative than carbon. This means that the -NO group will withdraw electron density from the conjugated system.

**Hint:** Consider the relative electronegativities of the atoms involved to determine how electron density is affected.

### Step 3: Resonance and Electron Withdrawal
- The -NO group can participate in resonance with the conjugated system. The electron density can shift towards the -NO group, leading to the formation of resonance structures.
- This electron withdrawal can be illustrated by the movement of double bonds towards the -NO group, resulting in a resonance structure where the -NO group carries a negative charge.

**Hint:** Visualize the resonance structures to understand how electron density shifts occur.

### Step 4: Identifying the Effects
- The electron-withdrawing nature of the -NO group leads to two specific effects:
- **Mesomeric Effect (M):** Since the -NO group withdraws electron density through resonance, it exhibits a negative mesomeric effect, denoted as -M.
- **Inductive Effect (I):** The electronegativity of nitrogen compared to carbon also causes the -NO group to withdraw electron density inductively, leading to a negative inductive effect, denoted as -I.

**Hint:** Recall the definitions of mesomeric and inductive effects to categorize the effects correctly.

### Step 5: Conclusion
- Therefore, at a conjugated position, the -NO group imparts both a negative mesomeric effect (-M) and a negative inductive effect (-I).

**Final Answer:** At conjugated position, -NO imparts -M and -I effects.