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Aldehydes, Ketones and Carboxylic Acids appeared 46 times across 3 years — 5.3% of Chemistry. This question is from Nucleophilic Addition Reactions.

Year 2026 2025 2024 Total
Questions 14 21 11 46
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The compound formed by the reaction of ethanal with semicarbazide contains ________ number of nitrogen atoms.

Numerical Answer Type:
Enter a numerical value Answer: 3 to 3 +4 marks

Solution & Explanation

Related Formula
CH₃-CHO + H₂N-NH-CO-NH₂ arrow CH₃-CH=N-NH-CO-NH₂ + H₂O
Core Logic

Ethanal (CH₃CHO) reacts with semicarbazide (H₂N-NH-CO-NH₂) via nucleophilic addition followed by elimination of water to form a semicarbazone.

Step 1: Product Analysis

The product is Ethanal semicarbazone: CH₃-CH=N-NH-CO-NH₂. Counting the nitrogen atoms in this structure:

  • The imine nitrogen (=N-)
  • The amine nitrogen (-NH-)
  • The amide nitrogen (-NH₂)

    • Total = 3 Nitrogen atoms.

Chapter Mix

Class 12 Chemistry: Aldehydes, Ketones and Carboxylic Acids

Reference Study Guides

Aldehydes Ketones And Carboxylic Acids

More Aldehydes, Ketones and Carboxylic Acids Previous-Year Questions — Page 10

Q jee_main_2024_31_jan_morning Reactions with Grignard Reagent
The product of the following reaction is P.
Reactions with Grignard Reagent diagram for Q84 - JEE Main 2024 Morning
The image shows p-hydroxybenzaldehyde reacting with one equivalent of PhMgBr followed by aqueous ammonium chloride.
The number of hydroxyl groups present in the product P is
Numerical Answer. Answer: 0 to 0

Solution

Core Logic

The given reactant is p-hydroxybenzaldehyde, which contains both a phenolic -OH group (acidic) and an aldehyde group (electrophilic).

When one equivalent of Grignard reagent (PhMgBr) is added, it behaves primarily as a strong base due to the presence of an acidic proton. Acid-base reactions are extremely fast compared to nucleophilic additions.

The acidic phenolic -OH reacts with PhMgBr:

PhMgBr + HO-C₆H₄-CHO arrow Ph-H (Benzene) + BrMg-O-C₆H₄-CHO

Upon workup with aq. NH₄Cl, the phenoxide ion simply regenerates the starting p-hydroxybenzaldehyde. However, the question asks for the number of hydroxyl groups present in the formed product (Benzene).

Reactions with Grignard Reagent diagram for Q84 - JEE Main 2024 Morning
The image shows p-hydroxybenzaldehyde reacting with one equivalent of PhMgBr followed by aqueous ammonium chloride.

The distinct product formed in the reaction is Benzene. Benzene has 0 hydroxyl groups.

Pattern Recognition

Whenever a Grignard reagent encounters a molecule with an acidic hydrogen (alcohol, phenol, amine, alkyne), it will invariably act as a base first. If only 1 equivalent is used, nucleophilic addition to carbonyls will NOT happen.

Chapter Mix

Class 12 Chemistry: Aldehydes, Ketones and Carboxylic Acids Class 12 Chemistry: Alcohols, Phenols and Ethers

More Aldehydes, Ketones and Carboxylic Acids Questions — jee_main_2024_30_jan_morning

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