Which is the correct order of acidity of the C-H bond in nitromethane, acetone, acetonitrile and methane?

A $CH X_{3} NO X_{2} > CH X_{3} CN > CH X_{3} COCH X_{3} > CH X_{4}$
B $CH X_{3} COCH X_{3} > CH X_{3} NO X_{2} > CH X_{3} CN > CH X_{4}$
C $CH X_{3} NO X_{2} > CH X_{3} COCH X_{3} > CH X_{3} CN > CH X_{4}$
D $CH X_{4} > CH X_{3} CN > CH X_{3} COCH X_{3} > CH X_{3} NO X_{2}$

Answer: C

Acidity follows the ability of the substituent to delocalise the negative charge of the carbanion: nitro (charge onto O of a nitronate) > carbonyl (enolate) > cyano (weaker) > hydrogen (none). Typical pKa values are about 10, 19, 25 and 50, which gives the order shown.

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Which is the correct order of acidity of the C-H bond in nitromethane, acetone, acetonitrile and methane?

Answer: C

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