Which of the following N-H bonds is the most acidic?

A $CH X_{3} CONH X_{2}$
B $(CH X_{3} CO) X_{2} NH$
C $(CH X_{3}) X_{2} NH$
D $CH X_{3} NH X_{2}$

Answer: B

Removing H+ from an imide gives an anion whose charge is delocalised over two carbonyl oxygens. An amide has only one carbonyl and amines have none, so the imide, diacetamide, is the most acidic (imides have pKa about 8-10 against about 15-17 for simple amides and above 30 for amines).

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