JEE Main · 2020 · 05 Sep 2020 · Shift 1 · Aldehydes Ketones and Carboxylic Acids

The increasing order of the acidity of the

α

-hydrogen of the following compounds is:

(A) (see structure)
(B) (see structure)
(C) (see structure)
(D) (see structure)

(A)(C) $<$ (A) $<$ (B) $<$ (D)
(B)(B) $<$ (C) $<$ (A) $<$ (D)
(C)(D) $<$ (C) $<$ (A) $<$ (B)✓ Correct
(D)(A) $<$ (C) $<$ (D) $<$ (B)

Answer: (C)

Solution

The acidity of an

α

-hydrogen is governed by how well the resulting enolate is stabilised. The

β

-diketone, whose central hydrogen leaves a charge delocalised over two carbonyls, is the most acidic. A simple ketone such as acetone, with just one carbonyl, comes next. The ester is less acidic still, because its alkoxy oxygen pushes electron density onto the carbonyl and destabilises the enolate; and the amide is the least acidic of all, since its nitrogen donates even more strongly into the carbonyl. The acidity therefore increases from the amide to the ester to the ketone to the

β

-diketone.

JEE Main · 2020 · 05 Sep 2020 · Shift 1 · Single correct option

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JEE Main · 2020 · 05 Sep 2020 · Shift 1 · Aldehydes Ketones and Carboxylic Acids

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