Which of the following is the weakest Brönsted base?

Options

A.
B.
C.
D. `CH_(3)NH_(2)`

Explanation

To determine which of the given options is the weakest Brönsted base, we need to understand the concept of Brönsted bases. A Brönsted base is defined as a species that can accept a proton (H⁺). The strength of a Brönsted base is influenced by the availability of the lone pair of electrons on the basic site (usually nitrogen in organic compounds containing nitrogen).

### Step-by-Step Solution:

1. **Identify the Compounds**: First, we need to identify the compounds provided in the options. Let's assume the options are:
- Option 1: NH₃ (Ammonia)
- Option 2: CH₃NH₂ (Methylamine)
- Option 3: C₂H₅NH₂ (Ethylamine)
- Option 4: Aniline (C₆H₅NH₂)

2. **Analyze Each Compound**:
- **NH₃ (Ammonia)**: This compound has a lone pair of electrons on nitrogen that can easily accept a proton. Thus, it is a good Brönsted base.
- **CH₃NH₂ (Methylamine)**: The methyl group (CH₃) is an electron-donating group (+I effect), which increases the electron density on nitrogen, making it a stronger base than ammonia.
- **C₂H₅NH₂ (Ethylamine)**: Similar to methylamine, the ethyl group (C₂H₅) also donates electron density to nitrogen, enhancing its basicity further.
- **Aniline (C₆H₅NH₂)**: In aniline, the lone pair of electrons on nitrogen can participate in resonance with the aromatic ring. This delocalization of the lone pair reduces the availability of the lone pair to accept a proton, making aniline a weaker base compared to the aliphatic amines.

3. **Compare Basicity**: Based on the analysis:
- NH₃ > CH₃NH₂ > C₂H₅NH₂ > Aniline in terms of basicity.
- Aniline has the least ability to accept a proton due to resonance stabilization, making it the weakest Brönsted base among the options.

4. **Conclusion**: Therefore, the weakest Brönsted base among the options provided is **Aniline (C₆H₅NH₂)**.

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