Which of fllowing is the weakest base ?

Options

A. ` NH_3`
B. `C_6H_5NH_2`
C. `C_6H_5CH_6NH_2`
D. `CH_3NH_2`

Explanation

To determine which of the following compounds is the weakest base, we need to analyze the basicity of each compound based on the availability of their lone pairs for donation. Here’s a step-by-step breakdown of the solution:

### Step 1: Identify the Compounds
The question provides us with several compounds. For this example, let's assume the compounds are:
1. NH3 (Ammonia)
2. C6H5NH2 (Aniline)
3. C6H5CH2NH2 (Benzylamine)
4. CH3NH2 (Methylamine)

### Step 2: Understand Basicity
Basicity refers to the ability of a compound to donate a lone pair of electrons. The more available the lone pair is for donation, the stronger the base will be.

### Step 3: Analyze Each Compound
1. **NH3 (Ammonia)**:
- Ammonia has a lone pair on nitrogen that is readily available for donation. Thus, it is a strong base.

2. **C6H5NH2 (Aniline)**:
- Aniline has a lone pair on nitrogen, but this lone pair is involved in resonance with the aromatic ring. This resonance delocalizes the lone pair, making it less available for donation. Therefore, aniline is a weaker base compared to ammonia.

3. **C6H5CH2NH2 (Benzylamine)**:
- Benzylamine has a nitrogen atom with a lone pair that is not involved in resonance with the aromatic ring. The presence of the CH2 group allows for some electron-donating effects, making the lone pair more available for donation. Thus, benzylamine is a stronger base than aniline.

4. **CH3NH2 (Methylamine)**:
- Methylamine has a lone pair on nitrogen that is also readily available for donation, similar to ammonia. Therefore, it is a strong base.

### Step 4: Compare Basicity
Now, we compare the basicity of the compounds:
- NH3: Strong base
- CH3NH2: Strong base
- C6H5CH2NH2: Moderate base
- C6H5NH2: Weakest base due to resonance effect

### Conclusion
From the analysis, we conclude that **C6H5NH2 (Aniline)** is the weakest base among the given options due to the resonance stabilization of its lone pair, which makes it less available for donation.

### Final Answer
**The weakest base is C6H5NH2 (Aniline).**

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