What is the order of basicity of the following compounds ?
(i) `CH_(3)NH_(2),(CH_(3))_(2)NH,(CH_(3))_(3)N` (in aprotic solvent)
(ii) `C_(2)H_(5)NH_(2)(C_(2)H_(5))_(2)NH,(C_(2)H_(5))_(3)N` (in aprotic solvent)

Answer

To determine the order of basicity of the given compounds in aprotic solvents, we will analyze the effects of alkyl groups on the nitrogen atom in each amine. The basicity of amines is influenced by the electron-donating ability of the alkyl groups attached to the nitrogen.

### Step-by-Step Solution:

**(i) For the compounds: `CH₃NH₂`, `(CH₃)₂NH`, `(CH₃)₃N`**

1. **Identify the types of amines:**
- `CH₃NH₂` is a primary amine.
- `(CH₃)₂NH` is a secondary amine.
- `(CH₃)₃N` is a tertiary amine.

2. **Consider the electron-donating effects:**
- Alkyl groups are electron-donating due to the +I (inductive) effect. The more alkyl groups attached to the nitrogen, the greater the electron density around the nitrogen atom, which enhances its ability to donate a lone pair of electrons.

3. **Rank the basicity:**
- Tertiary amines have the highest basicity because they have three alkyl groups donating electron density to the nitrogen.
- Secondary amines have moderate basicity with two alkyl groups.
- Primary amines have the lowest basicity with only one alkyl group.

4. **Conclusion for part (i):**
- The order of basicity in aprotic solvent is:
\[ (CH₃)₃N > (CH₃)₂NH > CH₃NH₂ \]

**(ii) For the compounds: `C₂H₅NH₂`, `(C₂H₅)₂NH`, `(C₂H₅)₃N`**

1. **Identify the types of amines:**
- `C₂H₅NH₂` is a primary amine.
- `(C₂H₅)₂NH` is a secondary amine.
- `(C₂H₅)₃N` is a tertiary amine.

2. **Consider the electron-donating effects:**
- Similar to the previous case, the presence of ethyl groups will enhance the basicity of the amines due to the +I effect.

3. **Rank the basicity:**
- Tertiary amine `(C₂H₅)₃N` will be the most basic due to three ethyl groups.
- Secondary amine `(C₂H₅)₂NH` will be next.
- Primary amine `C₂H₅NH₂` will have the lowest basicity.

4. **Conclusion for part (ii):**
- The order of basicity in aprotic solvent is:
\[ (C₂H₅)₃N > (C₂H₅)₂NH > C₂H₅NH₂ \]

### Final Answers:
1. For (i): \((CH₃)₃N > (CH₃)₂NH > CH₃NH₂\)
2. For (ii): \((C₂H₅)₃N > (C₂H₅)₂NH > C₂H₅NH₂\)