Acetamidine, $CH X_{3} C (= NH) NH X_{2}$ (pKaH about 12.4), is a far stronger base than acetamide (pKaH about $- 0.5$ ). The best explanation is that

Aprotonation at the imine nitrogen gives a symmetrical amidinium ion in which the charge is shared equally by two nitrogen atoms
Bamidine has a C=O group which withdraws electrons
Cthe amidine nitrogen lone pair is part of an aromatic sextet
Damidines are less sterically hindered than amides

Answer: A

Protonating the sp

^{2}

=NH nitrogen gives

CH X_{3} C (NH X_{2}) X_{2} X^{+}

, with two equivalent resonance structures sharing the charge between two N atoms, which are better donors than the oxygen of an amide. Acetamide protonates at O to give a less well stabilised cation.

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Acetamidine, CHX3​C(=NH)NHX2​ (pKaH about 12.4), is a far stronger base than acetamide (pKaH about −0.5). The best explanation is that

Answer: A

More questions on Basic strength of amines and heterocycles

Acetamidine, $CH X_{3} C (= NH) NH X_{2}$ (pKaH about 12.4), is a far stronger base than acetamide (pKaH about $- 0.5$ ). The best explanation is that