Consider the extremely basic guanidine molecule, . Upon undergoing successful protonation at the pri — GOC and Organic Chemistry Basics Chemistry Question
Question
Consider the extremely basic guanidine molecule, $HN=C(NH_2)_2$. Upon undergoing successful protonation at the primary basic site to form the guanidinium cation, exactly how many completely equivalent and energetically indistinguishable resonance structures (canonical forms) can be drawn to illustrate its extensive delocalization?
💡 Solution & Explanation
Protonation of guanidine occurs preferentially at the $sp^2$ hybridized imine nitrogen. The resulting positive charge is perfectly delocalized across all three nitrogen atoms via resonance with the adjacent non-bonding lone pairs on the two $NH_2$ groups. This extended $\pi$ -conjugation yields exactly 3 entirely equivalent and symmetrical resonance structures, conferring massive thermodynamic stability to the conjugate acid.