Select the most basic compound.

Options

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B.
C.
D.

Answer

To determine the most basic compound among the given structures, we need to analyze the substituents attached to the aniline (C6H5NH2) and their effects on the basicity of the nitrogen atom.

### Step-by-Step Solution:

1. **Identify the Structures**:
We have four structures of aniline with different substituents at the meta position. Let's denote them as:
- Structure 1: Aniline with a -NO2 (nitro) group
- Structure 2: Aniline with a -Cl (chloro) group
- Structure 3: Aniline with a -CH3 (methyl) group
- Structure 4: Aniline with a -F (fluoro) group

2. **Understand Basicity**:
Basicity in organic compounds is often related to the ability of the nitrogen atom to donate its lone pair of electrons. The presence of electron-withdrawing groups (EWGs) decreases basicity, while electron-donating groups (EDGs) increase basicity.

3. **Analyze Each Structure**:
- **Structure 1 (-NO2)**: The nitro group is a strong electron-withdrawing group (-I effect). It pulls electron density away from the nitrogen, making it less able to donate its lone pair. Thus, this structure is non-basic.

- **Structure 2 (-Cl)**: Chlorine is also an electron-withdrawing group, but it has a weaker -I effect compared to -NO2. It still decreases the basicity of the nitrogen, but not as significantly as the nitro group. Therefore, it is less basic than aniline but more basic than Structure 1.

- **Structure 3 (-CH3)**: The methyl group is an electron-donating group (+I effect). It increases the electron density on the nitrogen, making it more basic. Thus, this structure is more basic than Structures 1 and 2.

- **Structure 4 (-F)**: Fluorine is a strong electron-withdrawing group due to its high electronegativity (-I effect), which decreases the basicity of the nitrogen. However, it also has a +M effect (mesomeric effect) that can stabilize the lone pair to some extent. Still, it is less basic than Structure 3.

4. **Conclusion**:
Comparing the basicity of all four structures, Structure 3 with the -CH3 (methyl) group is the most basic due to its +I effect, which enhances the ability of the nitrogen to donate its lone pair of electrons.

### Final Answer:
The most basic compound is **Structure 3 (Aniline with a -CH3 group)**.

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