Among the following amines, the strongest Bronsted base is _________.

Options

A.
B. `NH_3`
C.
D.

Answer

To determine which amine among the given options is the strongest Bronsted base, we need to analyze the ability of each amine to accept a proton (H+). A Bronsted base is defined as a substance that can accept protons. The strength of a Bronsted base is influenced by the availability of the lone pair of electrons on the nitrogen atom in the amine. Here’s a step-by-step solution:

### Step 1: Understand the Concept of Bronsted Bases
A Bronsted base is a proton acceptor. The ability of an amine to act as a Bronsted base depends on how readily it can donate its lone pair of electrons to accept a proton.

**Hint:** Remember that the more available the lone pair of electrons on nitrogen, the stronger the Bronsted base.

### Step 2: Analyze the Structure of Each Amine
We need to look at the structure of each amine option to see how the lone pair on nitrogen is affected by other groups (like alkyl groups or aromatic systems).

**Hint:** Consider how substituents on the nitrogen atom can either donate electron density or withdraw it.

### Step 3: Evaluate Each Option
- **Option A:** The lone pair on nitrogen is involved in conjugation, making it less available to accept a proton.
- **Option B:** The lone pair is more available than in Option A, but still not optimal due to possible steric hindrance or other effects.
- **Option C:** Similar to Option A, the lone pair is involved in conjugation, reducing its availability.
- **Option D:** The nitrogen has an alkyl group attached, which exerts a +I (inductive) effect, increasing the electron density on nitrogen. This makes the lone pair more available for protonation.

**Hint:** Look for the presence of alkyl groups that can enhance basicity through the +I effect.

### Step 4: Compare Basicity
From the analysis:
- Options A, C, and possibly B have their lone pairs involved in conjugation or other interactions that reduce their basicity.
- Option D, with the alkyl group, has an increased electron density on nitrogen due to the +I effect, making it the strongest Bronsted base.

**Hint:** The presence of electron-donating groups increases the basicity of amines.

### Step 5: Conclusion
Based on the evaluations, the strongest Bronsted base among the given amines is **Option D**.

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