Which of the following has the most acidic C-H bond?

A $CH X_{3} COOC X_{2} H X_{5}$
B $CH X_{3} COCH X_{2} COCH X_{3}$
C $CH X_{3} CN$
D $CH X_{3} COCH X_{3}$

Answer: B

Deprotonating the central CH2 of pentane-2,4-dione gives an enolate whose charge is delocalised over two carbonyl oxygens (pKa about 9). Acetone has pKa about 19, acetonitrile about 25 and ethyl acetate about 25.

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