Which of the following is the strongest Bronsted base ?

Options

A.
B.
C.
D.

Explanation

To determine which of the given compounds is the strongest Bronsted base, we need to analyze the availability of lone pairs of electrons in each option. A stronger Bronsted base is one that can readily accept protons (H⁺ ions), which is often related to the availability of free lone pairs of electrons.

### Step-by-Step Solution:

1. **Identify the Compounds**:
Let's assume the compounds are:
- A: Aniline (C6H5NH2)
- B: Ammonia (NH3)
- C: Pyridine (C5H5N)
- D: A compound with a nitrogen atom bonded to two CH2 groups (e.g., N(CH2)2)

2. **Analyze Compound A (Aniline)**:
- In aniline, the lone pair on nitrogen is involved in resonance with the benzene ring. This delocalization reduces the availability of the lone pair for protonation, making aniline a weaker base.

**Hint**: Look for resonance structures that can delocalize lone pairs.

3. **Analyze Compound B (Ammonia)**:
- Ammonia has a lone pair of electrons on nitrogen that is not involved in resonance. Therefore, the lone pair is free and available for protonation, making ammonia a relatively strong base.

**Hint**: Check if the lone pair is involved in resonance or is free.

4. **Analyze Compound C (Pyridine)**:
- In pyridine, the lone pair on nitrogen is part of the aromatic system and is delocalized. This delocalization reduces the availability of the lone pair for protonation, making pyridine a weaker base than ammonia.

**Hint**: Consider the effects of aromaticity on lone pair availability.

5. **Analyze Compound D**:
- The compound with nitrogen bonded to two CH2 groups has a free lone pair on nitrogen. Additionally, the CH2 groups exert a +I (inductive) effect, which increases the electron density on nitrogen, enhancing its basicity.

**Hint**: Look for electron-donating groups that can increase basicity.

6. **Comparison of Basicity**:
- Based on the analysis:
- Aniline (A) is the weakest due to resonance.
- Pyridine (C) is weaker than ammonia (B) due to aromaticity.
- Ammonia (B) has a free lone pair but is not enhanced by any electron-donating groups.
- The compound D has a free lone pair and is enhanced by the +I effect from the CH2 groups.

7. **Conclusion**:
- Therefore, the strongest Bronsted base among the options is **Compound D**.

### Final Answer:
The strongest Bronsted base is **Option D**.