Which is most basic in aqueous solution ?

Options

A. `CH_(3)NH_(2)`
B. `(CH_(3))_(2)NH`
C. `(CH_(3))_(3)N`
D. `Ph-NH_(2)`

Explanation

To determine which compound is the most basic in an aqueous solution, we need to analyze the basicity of the given compounds, focusing on their structure and the effects of substituents.

### Step-by-Step Solution:

1. **Identify the Compounds**: Let's assume we are comparing three compounds: an aliphatic amine, an aromatic amine, and a substituted aliphatic amine (with methyl groups).

2. **Understand Basicity**: Basicity in aqueous solution is primarily determined by the availability of the lone pair of electrons on the nitrogen atom (in the case of amines). The more readily the lone pair can accept protons (H⁺), the more basic the compound is.

3. **Compare Aliphatic vs. Aromatic Amines**:
- Aliphatic amines are generally more basic than aromatic amines. This is because aromatic amines have a resonance effect where the lone pair on the nitrogen can delocalize into the aromatic ring, making it less available to accept protons.
- In contrast, aliphatic amines do not have this resonance stabilization, so their lone pairs are more available.

4. **Consider Substituents**:
- If we have a substituted aliphatic amine (e.g., with methyl groups), we need to consider the effect of these groups. Methyl groups have a +I (inductive) effect, which increases the electron density on the nitrogen, enhancing its basicity.
- However, bulky groups can create steric hindrance, which may impede the nitrogen’s ability to donate its lone pair.

5. **Evaluate the Compounds**:
- The aliphatic amine will be the most basic due to the availability of the lone pair.
- The substituted aliphatic amine may be less basic than the simple aliphatic amine due to steric hindrance, despite the +I effect from the methyl groups.
- The aromatic amine will be the least basic due to resonance stabilization reducing the availability of the lone pair.

6. **Conclusion**: Based on the analysis, the aliphatic amine is the most basic in aqueous solution, followed by the substituted aliphatic amine, and finally the aromatic amine.

### Final Answer:
The most basic compound in aqueous solution is the aliphatic amine.