Aldehydes, Ketones and Carboxylic Acids Previous Year Questions — JEE Main Chemistry
46 past-year Aldehydes, Ketones and Carboxylic Acids questions from JEE Main (Chemistry) — page 7.
Q1933 (2024)
Identify the name reaction.
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- $\text{Stephen reaction}$
- $\text{Etard reaction}$
- $\text{Gatterman-koch reaction}$
- $\text{Rosenmund reduction}$
### Core Logic
The reaction of benzene with carbon monoxide ($CO$) and hydrogen chloride ($HCl$) in the presence of anhydrous aluminium chloride ($AlCl_3$) and cuprous chloride ($CuCl$) to give benzaldehyde is known as the Gatterman-Koch reaction.
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### Pattern Recognition
$CO + HCl \rightarrow$ Formyl chloride intermediate (in situ) with Lewis acid $\rightarrow$ formylation of benzene. This is definitively the Gatterman-Koch formylation.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 12 Chemistry: Aldehydes, Ketones and Carboxylic Acids
Q2034 (2024)
The product of the following reaction is P.
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The number of hydroxyl groups present in the product P is
### 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 $PhMgBr$:
$$PhMgBr + HO-C_6H_4-CHO \rightarrow Ph-H (Benzene) + BrMg-O-C_6H_4-CHO$$
Upon workup with $aq. NH_4Cl$, 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).
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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.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 12 Chemistry: Aldehydes, Ketones and Carboxylic Acids
Class 12 Chemistry: Alcohols, Phenols and Ethers
Q61 (2026)
An organic compound “P” of molecular formula $C_{6}H_{12}O_{3}$ gives positive Iodoform test but negative Tollen’s test. When “P” is treated with dilute acid, it produces “Q”. “Q” gives positive Tollen’s test and also iodoform test. The structure of “P” is :
- $\mathrm{CH_3-CO-CH(OCH_3)-CH_2(OCH_3)}$
- $\mathrm{CH_3-CO-CH_2-CH(OCH_3)_2}$
- $\mathrm{H-CO-CH_2-CH_2-C(OCH_3)_2-CH_3}$
- $\mathrm{CH_3-CO-CO-CH_3} \text{ (with acetal structure)}$
### Core Logic
Compound P ($C_6H_{12}O_3$) gives a positive iodoform test, indicating it has a methyl ketone group ($CH_3CO-$). It gives a negative Tollen's test, indicating no free aldehyde group.
On acidic hydrolysis, P yields Q. Compound Q gives both positive iodoform test and Tollen's test, meaning Q contains both a methyl ketone and an aldehyde group.
Looking at the options, if P is an acetal of an aldehyde, acidic hydrolysis will regenerate the aldehyde.
Option 2 is $\mathrm{CH_3-CO-CH_2-CH(OCH_3)_2}$ (an acetal of aldehyde).
This compound 'P' has a $CH_3CO-$ group (positive iodoform) and an acetal (protected aldehyde, negative Tollen's).
On hydrolysis:
$$\mathrm{CH_3-CO-CH_2-CH(OCH_3)_2} \xrightarrow{\mathrm{H_2O/H^+}} \mathrm{CH_3-CO-CH_2-CHO} + 2\mathrm{CH_3OH}$$
The product Q ($\mathrm{CH_3-CO-CH_2-CHO}$) has a methyl ketone (positive iodoform test) and an aldehyde (positive Tollen's test).
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### Pattern Recognition
Whenever an aldehyde test becomes positive *after* hydrolysis, it points to a protected aldehyde, usually an acetal or hemiacetal. A compound with molecular formula $C_n H_{2n} O_3$ often represents a keto-acetal.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 12 Chemistry: Aldehydes, Ketones and Carboxylic Acids
Class 12 Chemistry: Alcohols, Phenols and Ethers
Q57 (2026)
Match List-I with List-II.
<div style="overflow-x: auto; margin: 1rem 0;"><table style="width: 100%; border-collapse: collapse; text-align: left; font-size: 14px;"><thead><tr><th style="border: 1px solid #888; padding: 8px;">List-I (Reagents)</th><th style="border: 1px solid #888; padding: 8px;">List-II (Reaction Name Involving Aldehydes)</th></tr></thead><tbody><tr><td style="border: 1px solid #888; padding: 8px;">A. $\text{H}_2, \text{Pd}-\text{BaSO}_4$</td><td style="border: 1px solid #888; padding: 8px;">I. Etard Reaction</td></tr><tr><td style="border: 1px solid #888; padding: 8px;">B. $\text{SnCl}_2, \text{HCl}$</td><td style="border: 1px solid #888; padding: 8px;">II. Rosenmund Reduction</td></tr><tr><td style="border: 1px solid #888; padding: 8px;">C. $\text{CrO}_2\text{Cl}_2, \text{CS}_2$</td><td style="border: 1px solid #888; padding: 8px;">III. Gatterman–Koch Reaction</td></tr><tr><td style="border: 1px solid #888; padding: 8px;">D. $\text{CO}, \text{HCl}, \text{Anhyd. } \text{AlCl}_3$</td><td style="border: 1px solid #888; padding: 8px;">IV. Stephen Reaction</td></tr></tbody></table></div>
Choose the correct answer from the options given below:
- $(1) \ A-\text{II}, B-\text{III}, C-\text{IV}, D-\text{I}$
- $(2) \ A-\text{IV}, B-\text{III}, C-\text{I}, D-\text{II}$
- $(3) \ A-\text{IV}, B-\text{I}, C-\text{II}, D-\text{III}$
- $(4) \ A-\text{II}, B-\text{IV}, C-\text{I}, D-\text{III}$
### Core Logic
- A. $\text{H}_2, \text{Pd}-\text{BaSO}_4 \rightarrow$ II. Rosenmund Reduction
- B. $\text{SnCl}_2, \text{HCl} \rightarrow$ IV. Stephen Reaction
- C. $\text{CrO}_2\text{Cl}_2, \text{CS}_2 \rightarrow$ I. Etard Reaction
- D. $\text{CO}, \text{HCl}, \text{Anhyd. } \text{AlCl}_3 \rightarrow$ III. Gatterman–Koch Reaction
### Step 1: Final Conclusion
Combining the correct matching gives A-II, B-IV, C-I, D-III, which is option (4).
### Pattern Recognition
Sees: standard name reactions for aldehyde preparation.
Trap: Confusing Etard reagent with Gatterman-Koch or Stephen reduction.
### Chapter Mix
Class 12 Chemistry: Aldehydes, Ketones and Carboxylic Acids
Q63 (2026)
Match the LIST-I with LIST-II
<div style="overflow-x: auto; margin: 1rem 0;"><table style="width: 100%; border-collapse: collapse; text-align: left; font-size: 14px;"><thead><tr><th style="border: 1px solid #888; padding: 8px;">List-I (Reagents)</th><th style="border: 1px solid #888; padding: 8px;">List-II (Name of Reaction involving carbonyl compound)</th></tr></thead><tbody><tr><td style="border: 1px solid #888; padding: 8px;">A. $NH_{2}-NH_{2}$, KOH</td><td style="border: 1px solid #888; padding: 8px;">I. Tollen's Test</td></tr><tr><td style="border: 1px solid #888; padding: 8px;">B. $Ag(NH_{3})_{2}OH$</td><td style="border: 1px solid #888; padding: 8px;">II. Clemmensen Reduction</td></tr><tr><td style="border: 1px solid #888; padding: 8px;">C. Aq. $CuSO_{4}$, Sodium Potassium tartarate, KOH</td><td style="border: 1px solid #888; padding: 8px;">III. Wolff-Kishner Reduction</td></tr><tr><td style="border: 1px solid #888; padding: 8px;">D. Zn - Hg, HCl</td><td style="border: 1px solid #888; padding: 8px;">IV. Fehling's Test</td></tr></tbody></table></div>
Choose the correct answer from the options given below
- $\text{A-III, B-I, C-IV, D-II}$
- $\text{A-II, B-I, C-IV, D-III}$
- $\text{A-IV, B-III, C-II, D-I}$
- $\text{A-III, B-IV, C-I, D-II}$
### Core Logic
(A) $NH_2-NH_2 / KOH$: Hydrazine with base is used in Wolff-Kishner Reduction to reduce carbonyls to alkanes. (A $\rightarrow$ III)
(B) $[Ag(NH_3)_2]OH$: Ammoniacal silver nitrate is Tollen's reagent, used in Tollen's Test to differentiate aldehydes from ketones. (B $\rightarrow$ I)
(C) Aqueous $CuSO_4$ + Sodium Potassium Tartrate + KOH: This is Fehling's solution (mixture of Fehling A and Fehling B). Used in Fehling's Test. (C $\rightarrow$ IV)
(D) $Zn-Hg / HCl$: Zinc amalgam with concentrated hydrochloric acid is the reagent for Clemmensen Reduction. (D $\rightarrow$ II)
### Step 1: Final Matching
The correct matches are A-III, B-I, C-IV, D-II.
### Pattern Recognition
Pure factual matching strictly based on NCERT name reactions and distinguishing tests for carbonyl compounds.
### Evaluation Rubric / Model Answer
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### Chapter Mix
Class 12 Chemistry: Aldehydes Ketones and Carboxylic Acids
