Question

Guanidine, $\left( NH _{2}\right)_{2} C = NH$, is said to be the strongest nitrogen containing organic base because:

• A. It has two $- NH _{2}$ groups.
• B. It has three nitrogen atoms that can be protonated.
• C. It is less stable as compared to the protonated species.
• D. Its conjugate acid is very much stable due to three equivalent structure.

Answer 1

Answer: (C), (D)

On the basis of hybridisation, $N \left(s p^{3}\right)$ of $NH _{2}$ with less $s$ character should be more basic than $N \left(s p^{2}\right)$ of the aimino $(= NH )$ group. However, $N$ of imino group is more basic and it is this nitrogen which is protonated because its conjugate acid is resonance hybrid of three equivalent structure which accounts its unusual stability.