Which of the following order of basicity is correct in aqueous medium?

Options

A. `(CH_(3))_(2)NH gt (CH_(3))_(3)N gt CH_(3)NH_(2)`
B. `(CH_(3))_(2)NH gt CH_(3)NH_(2) gt (CH_(3))_(3)N`
C. `(C_(2)H_(5))_(2)NH gt (C_(2)H_(5))_(3)N gt C_(2)H_(5)NH_(2)`
D. `(C_(2)H_(5))_(2)NH gt C_(2)H_(5)NH_(2) gt (C_(2)H_(5))_(3)N`

Answer

To determine the correct order of basicity of amines in aqueous medium, we need to consider the factors that influence basicity, such as hydrogen bonding and the electron-donating effects of alkyl groups.

### Step-by-Step Solution:

1. **Understanding Basicity in Aqueous Medium**:
- Basicity refers to the ability of a compound to accept protons (H⁺ ions).
- In aqueous medium, the basicity of amines is influenced by their ability to form hydrogen bonds and the stability of their conjugate acids (the protonated form of the amine).

2. **Effect of Alkyl Groups**:
- Alkyl groups are electron-donating groups (through +I effect), which increase the electron density on the nitrogen atom of the amine. This makes the nitrogen more capable of donating its lone pair of electrons to a proton, thus increasing basicity.
- However, the steric hindrance caused by larger alkyl groups can also affect basicity.

3. **Comparing Different Amines**:
- For amines with methyl groups (CH₃):
- **Secondary amine (R₂NH)**: More basic due to less steric hindrance and more electron-donating effects.
- **Primary amine (RNH₂)**: Less basic than secondary amines but more basic than tertiary amines.
- **Tertiary amine (R₃N)**: Least basic due to increased steric hindrance, which makes it harder for the nitrogen to approach and bond with a proton.
- Therefore, the order of basicity for amines with methyl groups in aqueous medium is: **Secondary > Primary > Tertiary**.

4. **Considering Ethyl Groups (C₂H₅)**:
- For amines with ethyl groups (C₂H₅):
- The same trend applies, but due to the larger size of the ethyl group, steric hindrance becomes more significant.
- Thus, the order of basicity for ethyl-substituted amines is: **Secondary > Tertiary > Primary**.

5. **Conclusion**:
- Based on the analysis, the correct order of basicity in aqueous medium is:
- For methyl-substituted amines: **Secondary > Primary > Tertiary**
- For ethyl-substituted amines: **Secondary > Tertiary > Primary**

### Final Answer:
The correct order of basicity in aqueous medium is:
- For CH₃: Secondary > Primary > Tertiary
- For C₂H₅: Secondary > Tertiary > Primary