In which of the following molecules `pi`-electron density in ring is minimum :

Options

A.
B.
C.
D.

Answer

To determine in which of the given molecules the π-electron density in the ring is minimum, we need to analyze the effect of substituents on the benzene ring. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand the Concept of Electron Density
- The π-electron density in a benzene ring can be influenced by substituents attached to it.
- Electron-donating groups (EDGs) increase the electron density in the ring, while electron-withdrawing groups (EWGs) decrease it.

### Step 2: Identify the Types of Substituents
- **Electron Donating Groups (EDGs)**: These groups donate electrons to the ring, increasing electron density. Examples include -OH, -OCH3, and -NH2.
- **Electron Withdrawing Groups (EWGs)**: These groups pull electrons away from the ring, decreasing electron density. Examples include -NO2, -CN, and -COOH.

### Step 3: Analyze the Given Molecules
- Suppose we have the following substituents attached to a benzene ring:
1. OCH3 (methoxy group) - EDG
2. NO2 (nitro group) - EWG
3. NH2 (amino group) - EDG
4. Two NO2 groups - EWG

### Step 4: Determine the Effect on Electron Density
- For the molecule with the **OCH3** group, the electron density will increase due to the EDG effect.
- For the molecule with the **NO2** group, the electron density will decrease due to the EWG effect.
- For the molecule with the **NH2** group, the electron density will also increase due to the EDG effect.
- For the molecule with **two NO2 groups**, the electron density will be significantly decreased because both groups are electron-withdrawing.

### Step 5: Conclusion
- Among the options, the molecule with **two NO2 groups** will have the minimum π-electron density in the ring due to the strong electron-withdrawing effect of both substituents.

### Final Answer
- The molecule with the minimum π-electron density in the ring is the one with **two NO2 groups** (Option D).

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