JEE Main · 2021 · 20 Jul 2021 · Shift 1 · Aldehydes Ketones and Carboxylic Acids

The number of nitrogen atoms in a semicarbazone molecule of acetone is ____.

Answer: 3

Solution

Semicarbazide,

H_{2} N - NH - CO - N H_{2}

, carries three nitrogen atoms, and only the

- N H_{2}

attached to the other nitrogen is nucleophilic enough to attack a carbonyl carbon, the amide nitrogen being deactivated by the adjacent carbonyl. With acetone it condenses and loses water:

(C H_{3})_{2} CO + H_{2} N - NH - CO - N H_{2} ⟶ (C H_{3})_{2} C = N - NH - CO - N H_{2} + H_{2} O

The water carries away only oxygen and hydrogen, so every nitrogen of the reagent is retained and the semicarbazone of acetone contains 3 nitrogen atoms.

JEE Main · 2021 · 20 Jul 2021 · Shift 1 · Integer answer

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