Which of the following reagent is suitable for the preparation of the product in the above reaction ? (reaction of ketone to alkane)
1
NaBH4
2
NH2-NH2/C2H5ONa
3
Ni/H2
4
Red P + Cl2
Official Solution
Correct Option: (2)
Step 1: To convert a Carbonyl group ( ) directly into a Methylene group ( ), we use deoxygenation methods.
Step 2:Wolff-Kishner Reduction uses Hydrazine ( ) and a strong base (like or ) in ethylene glycol.
Step 3:Clemmensen Reduction ( ) is the other common method.
Step 4: and would only reduce the ketone to an alcohol.
02
PYQ 2021
medium
chemistryID: jee-main
Consider the above reaction, the product 'X' and 'Y' respectively are
1
A
2
B
3
C
4
D
Official Solution
Correct Option: (1)
Step 1: This is an Aldol Condensation of cyclopentanone.
Step 2: In the presence of dil. , one molecule of cyclopentanone forms an enolate and attacks another molecule to form the -hydroxy ketone (Product 'X'). Step 3: Upon heating (often in acidic medium for final dehydration), a molecule of water is lost to form the -unsaturated ketone (Product 'Y').
03
PYQ 2021
medium
chemistryID: jee-main
In Tollen's test for aldehyde, the overall number of electron(s) transferred to the Tollen's reagent formula [Ag(NH₃)₂]⁺ per aldehyde group to form silver mirror is __________. (Round off to the Nearest Integer).
Official Solution
Correct Option: (1)
Step 1: .
Step 2: .
Step 3: For every 1 mole of aldehyde oxidized, 2 moles of are reduced to . Total electrons transferred = 2.
04
PYQ 2021
medium
chemistryID: jee-main
Considering the reaction of Benzene with CO and HCl in the presence of anhydrous AlCl₃/CuCl (Gattermann-Koch reaction), identify product X :
1
A
2
B
3
C
4
D
Official Solution
Correct Option: (3)
Step 1: This set of reagents ( ) defines the **Gattermann-Koch reaction**.
Step 2: The reaction involves the formylation of the aromatic ring.
Step 3: Benzene is converted directly to Benzaldehyde ( ).
05
PYQ 2021
medium
chemistryID: jee-main
The major product of the following chemical reaction is : R-CN ? (Using as the alkyl group from the prompt skeleton)
1
Alcohol
2
Anhydride
3
Alkane
4
Aldehyde
Official Solution
Correct Option: (4)
Step 1: (Complete hydrolysis of Nitrile to Carboxylic Acid).
Step 2: (Formation of Acid Chloride).
Step 3: is the Rosenmund Reduction.
Step 4: The acid chloride is reduced specifically to an aldehyde.
06
PYQ 2024
medium
chemistryID: jee-main
Given below are two statements : Statement I : Acidity of -hydrogens of aldehydes and ketones is responsible for Aldol reaction. Statement II : Reaction between benzaldehyde and ethanal will NOT give Cross – Aldol product.In the light of above statements, choose the most appropriate answer from the options given below.
1
Both Statement I and Statement II are correct.
2
Both Statement I and Statement II are incorrect.
3
Statement I is incorrect but Statement II is correct.
4
Statement I is correct but Statement II is incorrect.
Official Solution
Correct Option: (4)
Explanation of Statement I:
Aldehydes and ketones with at least one -hydrogen can undergo an aldol reaction due to the acidity of the -hydrogens. This acidity allows the formation of an enolate ion, which then attacks the carbonyl carbon of another molecule, leading to the aldol product. Therefore, Statement I is correct.
Explanation of Statement II:
Benzaldehyde does not contain an -hydrogen, so it cannot form an enolate ion. However, ethanol (in this context, likely meaning acetaldehyde) does have -hydrogens and can participate in the aldol reaction with itself or with other compounds that can form enolate ions. Thus, a cross-aldol product can form between benzaldehyde and acetaldehyde (ethanal). Therefore, Statement II is incorrect.
Conclusion:
Statement I is correct, but Statement II is incorrect. The correct answer is Option (4).
07
PYQ 2026
medium
chemistryID: jee-main
Given below are two statements :
Statement I : The condensation reaction between and under optimum pH will produce .
Statement II : The molecule, will generate in the presence of dilute acid.
In the light of the above statements, choose the correct answer from the options given below :
1
Both Statement I and Statement II are true
2
Both Statement I and Statement II are false
3
Statement I is true but Statement II is false
4
Statement I is false but Statement II is true
Official Solution
Correct Option: (1)
Step 1: Understanding the Concept:
Statement I refers to the nucleophilic addition-elimination reaction of carbonyls with ammonia derivatives. Statement II refers to the instability of hemiacetals in acidic media. Step 2: Detailed Explanation: Statement I: Acetaldehyde ( ) reacts with semicarbazide ( ) to form a semicarbazone. The reaction is a condensation (loss of ) and occurs optimally at pH 3.5. Thus, Statement I is True. Statement II: The given molecule is a hemiacetal (formed from benzaldehyde and methanol). Hemiacetals are unstable and readily revert to the parent aldehyde and alcohol in the presence of dilute acid. Thus, Statement II is True. Step 3: Final Answer:
Both statements are true.
08
PYQ 2026
hard
chemistryID: jee-main
The unsaturated ether on acidic hydrolysis produces carbonyl compounds as shown below. Based on this, predict the solution/reagent that will help to distinguish "P" and "Q" obtained in the reaction.
1
2,4-DNP reagent
2
Saturated NaHSO solution
3
Fehling solution
4
Lucas reagent
Official Solution
Correct Option: (3)
Step 1: Nature of products. Acidic hydrolysis produces one aldehyde and one ketone. Step 2: Differentiation. Fehling solution gives a positive test with aldehydes but not with ketones. Step 3: Conclusion. Fehling solution can distinguish between P and Q.
09
PYQ 2026
medium
chemistryID: jee-main
A student is given one compound among the following compounds that gives positive test with Tollen's reagent. The compound is:
1
B
2
A
3
C
4
D
Official Solution
Correct Option: (3)
Step 1: Understanding Tollen’s reagent test. Tollen’s reagent gives a positive test with aldehydes and compounds that can form aldehydes under reaction conditions. Step 2: Analysing the given compounds. Compound A and B: These are acetals/ethers. Acetals do not undergo oxidation by Tollen’s reagent and hence do not give a positive test. Compound D: This compound is an alcohol without the ability to form an aldehyde under Tollen’s test conditions. Hence, it does not give a positive test. Compound C: This compound is a hemiacetal. Hemiacetals are in equilibrium with aldehydes in aqueous medium. The aldehyde formed reacts with Tollen’s reagent to produce silver mirror. Step 3: Conclusion. Only compound C gives a positive Tollen’s test.
10
PYQ 2026
medium
chemistryID: jee-main
Observe the following reaction and same reaction is carried out with the following compound: X and Y can be differentiated by:
1
Fehling’s test
2
2,4-DNP
3
NaHSO
4
Lucas test
Official Solution
Correct Option: (1)
Step 1: Identify the type of reaction. The reaction shown is acid-catalysed cleavage of vinyl ether, which produces an aldehyde and a ketone. Step 2: Identify products X and Y. On hydrolysis:
Here,
Step 3: Select appropriate test for differentiation. Fehling’s test is positive for aldehydes and negative for ketones. Thus:
Step 4: Conclusion. Hence, Fehling’s test can differentiate X and Y.
11
PYQ 2026
easy
chemistryID: jee-main
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.
1
Statement I is false but Statement II is true
2
Both Statement I and Statement II are false
3
Statement I is true but Statement II is false
4
Both Statement I and Statement II are true
Official Solution
Correct Option: (3)
Step 1: Analysis of Statement I. Cross aldol condensation between two aldehydes having -hydrogens can form four products due to self and cross reactions. Hence, Statement I is true. Step 2: Analysis of Statement II. Semicarbazide reacts with both aldehydes and ketones. Benzaldehyde reacts faster than acetophenone due to less steric hindrance. Hence, Statement II is false. Step 3: Conclusion. Statement I is true, but Statement II is false.
12
PYQ 2026
medium
chemistryID: jee-main
Statement-I: Two different aldehydes on cross aldol condensation always give four products. Statement-II: Among benzaldehyde and acetophenone, only acetophenone reacts with semicarbazide.
1
Statement-I and Statement-II both are correct
2
Statement-I is incorrect, Statement-II is correct
3
Statement-I is correct, Statement-II is incorrect
4
Statement-I and Statement-II both are incorrect
Official Solution
Correct Option: (3)
Statement-I Analysis: If both aldehydes possess -hydrogen, then cross aldol condensation can give four products. If only one aldehyde has -hydrogen, then only three products are formed. Hence, Statement-I is correct. Statement-II Analysis: Both benzaldehyde and acetophenone contain carbonyl group and react with semicarbazide to form semicarbazones. Thus, Statement-II is incorrect.
13
PYQ 2026
medium
chemistryID: jee-main
Which of the following are the compound(s) that do not give Tollen's test?
1
A, B
2
C, D
3
A, C
4
B, D
Official Solution
Correct Option: (1)
Step 1: Understanding Tollen's test. Tollen's test is used to identify aldehydes, which reduce the Tollen's reagent to silver, forming a mirror-like coating. Compounds without an aldehyde group (such as acetals) will not give this test. Step 2: Analyzing the options. In option (A) and (B), both compounds are acetals (i.e., they do not have an aldehyde group). Therefore, they will not give the Tollen's test. Step 3: Conclusion. Hence, the correct answer is (1), A and B do not give Tollen's test.
14
PYQ 2026
medium
chemistryID: jee-main
Which of the following gives positive test ?
1
1
2
2
3
3
4
4
Official Solution
Correct Option: (3)
test is used for the detection of aldehydes . Both (3) and (4) contain the aldehyde group. In the presence of reagent, the aldehyde group is oxidized to a carboxylate ion, forming a silver mirror. Since option (3) is marked as the correct answer, we confirm that gives a positive test.
