basicity of amines

Question

Correct decreasing basicity order in aqueous solution:

RankGuru · Accepted Answer

1. **Basicity in Aqueous Solution**: Determined by three competing factors:
   - **Inductive Effect ($+I$)**: More methyl groups push electrons to N, increasing basicity ($3^\circ > 2^\circ > 1^\circ > NH_3$).
   - **Solvation Effect**: Protonated amines are stabilized by hydrogen bonding with water ($NH_4^+ > 1^\circ > 2^\circ > 3^\circ$).
   - **Steric Hindrance**: Bulky alkyl groups block the approach of protons ($NH_3 > 1^\circ > 2^\circ > 3^\circ$).
2. **Methyl Case**: The combined effect for methyl substituents leads to the experimental order: **$(CH_3)_2NH > CH_3NH_2 > (CH_3)_3N > NH_3$**.
3. **Note**: For ethyl groups, the order changes slightly to $Et_2NH > Et_3N > EtNH_2 > NH_3$.

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Gas phase basicity order (strongest base first) is typically: