Compare the acidic strength of the following (1 = least acidic, 4 = most acidic). For butan-2-one, consider the α C-H proton; for propanamide, consider the N-H proton.
(a) (b)
(c) (d)

Question

Compare the acidic strength of the following (1 = least acidic, 4 = most acidic). For butan-2-one, consider the α C-H proton; for propanamide, consider the N-H proton. (a) (b) (c) (d)

TestHub · Accepted Answer

Conjugate bases : (a) propanoate, charge delocalised equally over two oxygens (pKa ≈ 4.9); (c) the amide anion, charge delocalised from nitrogen onto the carbonyl oxygen (pKa ≈ 15-17); (d) ethoxide, localised on oxygen (pKa ≈ 16); (b) the ketone α-carbanion, charge shared with carbon (pKa ≈ 20). So propanoic acid > propanamide N-H > ethanol > butan-2-one α-H, i.e. a > c > d > b.

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