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

Year 2026 2025 2024 Total
Questions 14 21 11 46
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Given below are two statements : Statement I : Cross aldol condensation between two different aldehydes will always produce four different products. Statement II : When semicarbazide reacts with a mixture of benzaldehyde and acetophenone under optimum pH, it forms a condensation product with acetophenone only. In the light of the above statements, choose the correct answer from the options given below :

Solution & Explanation

Core Logic

Statement I: Cross aldol condensation between two different aldehydes yields four different products ONLY IF both aldehydes have α-hydrogens. If one aldehyde lacks α-hydrogens (e.g., benzaldehyde or formaldehyde), it can only act as an electrophile, resulting in fewer than four products (typically 2). Hence, the word "always" makes Statement I false.

Statement II: Semicarbazide (H₂N-NH-CO-NH₂) reacts with both aldehydes and ketones to form semicarbazones. Therefore, it will react with both benzaldehyde and acetophenone, not just acetophenone. Hence, Statement II is false.

Step 1: Conclusion

Both Statement I and Statement II are false.

Pattern Recognition

In organic statement questions, absolute words like "always" are strong indicators of false statements, as special cases (like no α-H) frequently break the general rule.

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_2026_24_january_evening

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