4-Nitrobutan-2-one, $CH X_{3} - CO - CH X_{2} - CH X_{2} - NO X_{2}$ , is treated with one equivalent of a weak base. Which hydrogen is removed most easily?

AAll the C-H bonds are equally acidic
BA hydrogen of the $CH X_{2}$ next to $C = O$ (C-3)
CA hydrogen of the $CH X_{3}$ next to $C = O$ (C-1)
DA hydrogen of the $CH X_{2}$ attached to $NO X_{2}$ (C-4)

Answer: D

The candidates are C-1 and C-3 (alpha to a ketone,

p K_{a} \approx 19

20

) and C-4 (alpha to a nitro group,

p K_{a} \approx 10

for nitroalkanes). The nitronate ion delocalises charge onto two oxygens and is much more stable than a ketone enolate. So the C-4 hydrogens are by far the most acidic.

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4-Nitrobutan-2-one, CHX3​−CO−CHX2​−CHX2​−NOX2​, is treated with one equivalent of a weak base. Which hydrogen is removed most easily?

Answer: D

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4-Nitrobutan-2-one, $CH X_{3} - CO - CH X_{2} - CH X_{2} - NO X_{2}$ , is treated with one equivalent of a weak base. Which hydrogen is removed most easily?