As the base changes from `RNH_(2)` to `R_(2)NH_(1)` to `R_(3)N` the basicity

Options

A. `R_(2)NH gt R_(3)N gt RNH_(2)`
B. `RNH_(2) gt R_(3)H gt R_(2)NH`
C. `RNH_(2) gt R_(2)NH gt R_(3)N`
D. `R_(3)N gt RNH_(2) gt R_(2)NH.`

Answer

To determine the basicity order of the compounds RNH₂ (primary amine), R₂NH (secondary amine), and R₃N (tertiary amine), we need to analyze the factors that influence basicity in amines.

### Step-by-Step Solution:

1. **Identify the Compounds**:
- RNH₂ is a primary amine.
- R₂NH is a secondary amine.
- R₃N is a tertiary amine.

2. **Understand Basicity**:
Basicity in amines is primarily determined by the availability of the lone pair of electrons on the nitrogen atom. The more available the lone pair is, the stronger the base.

3. **Effect of Alkyl Groups**:
Alkyl groups (R groups) are electron-donating due to the +I (inductive) effect. The more alkyl groups attached to the nitrogen, the more electron density is pushed towards the nitrogen, making the lone pair more available for bonding with protons (H⁺).

4. **Order of Basicity Without Steric Hindrance**:
- R₃N (tertiary amine) would generally be expected to be the strongest base because it has three alkyl groups donating electron density.
- R₂NH (secondary amine) would be next, with two alkyl groups.
- RNH₂ (primary amine) would be the weakest base with only one alkyl group.

Thus, the initial order based on the +I effect would be:
\[ \text{R}_3\text{N} > \text{R}_2\text{NH} > \text{RNH}_2 \]

5. **Consider Steric Hindrance**:
However, as the number of alkyl groups increases, steric hindrance also increases. This steric hindrance can make it more difficult for the nitrogen to approach a proton (H⁺), thus affecting basicity.

6. **Revised Order of Basicity**:
- The steric hindrance is more significant in tertiary amines (R₃N) compared to secondary (R₂NH) and primary (RNH₂) amines.
- Therefore, the effective order of basicity, considering both the +I effect and steric hindrance, is:
\[ \text{R}_2\text{NH} > \text{R}_3\text{N} > \text{RNH}_2 \]

7. **Final Conclusion**:
The correct order of basicity is:
\[ \text{R}_2\text{NH} > \text{R}_3\text{N} > \text{RNH}_2 \]