Question

The correct order of increasing basic nature for the bases $NH _3, CH _3 NH _2$ and $CH _3 NH$ in aqueous solutions is:

• A. $\text{C}\left(\text{H}\right)_{3} \, \text{N}\left(\text{H}\right)_{2} < \text{N}\left(\text{H}\right)_{3} < \left(\text{C} \left(\text{H}\right)_{3}\right)_{2}\text{N}\text{H}$
• B. $\text{N}\left(\text{H}\right)_{3} < \text{C}\left(\text{H}\right)_{3}\text{N}\left(\text{H}\right)_{2} < \left(\text{C} \left(\text{H}\right)_{3}\right)_{2}\text{N}\text{H}$
• C. $\text{C}\left(\text{H}\right)_{3}\text{N}\left(\text{H}\right)_{2} < \left(\text{C} \left(\text{H}\right)_{3}\right)_{2}\text{N}\text{H} < \text{N}\left(\text{H}\right)_{3}$
• D. $\left(\text{C} \left(\text{H}\right)_{3}\right)_{2}\text{N}\text{H} < \text{N}\left(\text{H}\right)_{3} < \text{C}\left(\text{H}\right)_{3}\text{N}\left(\text{H}\right)_{2}$

Answer 1

Answer: (B)

If the alkyl group is bigger than $\text{C}\text{H}_{3}$ group, there is steric hindrance to H-bonding and hence $+ \, \text{I}$ effect predomtextnates over H-bonding. $2>3>1$ . There is an important role of the inductive effect, solvation effect and steric hindrance of alkyl group, which decides the basic strength of alkyl amine in the aqueous state.
$\left(\text{C} \left(\text{H}\right)_{3}\right)_{2} \, \text{N}\text{H}>\text{C}\left(\text{H}\right)_{3}\text{N}\left(\text{H}\right)_{2}>\text{N}\left(\text{H}\right)_{3}$