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Aldehydes, Ketones and Carboxylic Acids

JEE Main 2026 (Online) 23rd January Evening ShiftNumericalMedium📈 Topic in 27% papers+4
Ques. 1JEE Main 2026, 23 January (Evening Shift)

Consider the following reaction of benzene. [figure] In compound (Q), the percentage of oxygen is %. (Nearest integer)

Answer

10

Solution

Step 1 (Friedel–Crafts acylation): the acyl chloride end (-COCl) acylates benzene in the presence of anhydrous AlCl3, giving P (1-phenylpentane-1,4-dione), C6H5COCH2CH2COCH3.

Step 2 (intramolecular aldol condensation): P is a 1,4-diketone. With aq NaOH the carbanion formed at the terminal CH3 attacks the C=O carbon attached to the ring, giving a five-membered ring; on heating, the aldol loses H2O to give a conjugated enone.

[figure]

Q = 3-phenylcyclopent-2-en-1-one, C11H10O

Molar mass = 11(12) + 10(1) + 16 = 158 g mol-1

\% O = 16158 100 = 10.13\% 10

Answer: 10

Keep practising — Aldehydes, Ketones and Carboxylic Acids

Ques. 2JEE Main 2026, 22 January (Morning Shift)

Match the LIST-I with LIST-II Choose the correct answer from the options given below :

  1. A-IV, B-III, C-II, D-I
  2. A-III, B-I, C-IV, D-II
  3. A-II, B-I, C-IV, D-III
  4. A-III, B-IV, C-I, D-II
Ques. 3JEE Main 2026, 22 January (Evening Shift)

The compound A, C8H8O2 reacts with acetophenone to form a single product via cross-Aldol condensation. The compound A on reaction with conc. NaOH forms a substituted benzyl alcohol as one of the two products. The compound A is :

  1. 2-hydroxy acetophenone
  2. 4-hydroxy benzaldehyde
  3. 4-methyl benzoic acid
  4. 4-methoxy benzaldehyde
Ques. 4JEE Main 2026, 21 January (Morning Shift)

An organic compound "P" of molecular formula C6H12O3 gives positive iodoform test but negative Tollens' test. When "P" is treated with dilute acid, it produces "Q". "Q" gives positive Tollens' test and also iodoform test. The structure of "P" is :

  1. H- O \|C-CH2-CH2- OCH3 |CH-OCH3
  2. CH3- O \|C- OCH3 |CH- OCH3 |CH2
  3. CH3- O \|C-CH2- OCH3 |CH-OCH3
  4. CH3- O \|C- OCH3 | OCH3 |C-CH3
Ques. 5JEE Main 2026, 21 January (Evening Shift)

Match List - I with List - II. Choose the correct answer from the options given below :

  1. A-II, B-III, C-IV, D-I
  2. A-IV, B-III, C-I, D-II
  3. A-IV, B-I, C-II, D-III
  4. A-II, B-IV, C-I, D-III
Ques. 6JEE Main 2025, 8 April (Evening Shift)

A [(ii) H3O+](i) NaOH B [(ii) H2SO4, ](i) EtOH C 'A' shows positive Lassaigne's test for N and its molar mass is 121. 'B' gives effervescence with aq NaHCO3. 'C' gives fruity smell. Identify A, B and C from the following.

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
Ques. 7JEE Main 2025, 8 April (Evening Shift)

When [figure] undergoes intramolecular aldol condensation, the major product formed is :

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
Ques. 8JEE Main 2025, 7 April (Morning Shift)

Which of the following compounds is least likely to give effervescence of CO2 in presence of aq. NaHCO3?

  1. Ph- NH3 Cl
  2. [figure]
  3. [figure]
  4. [figure]
Ques. 9JEE Main 2025, 7 April (Evening Shift)

"P" is an optically active compound with molecular formula C6H12O. When "P" is treated with 2,4-dinitrophenylhydrazine, it gives a positive test. However, in presence of Tollens' reagent, "P" gives a negative test. Predict the structure of "P".

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
Ques. 10JEE Main 2025, 4 April (Morning Shift)

Aldol condensation is a popular and classical method to prepare , -unsaturated carbonyl compounds. This reaction can be both intermolecular and intramolecular. Predict which one of the following is not a product of intramolecular aldol condensation?

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
Ques. 11JEE Main 2025, 4 April (Evening Shift)

Which among the following compounds give yellow solid when reacted with NaOI/NaOH? Choose the correct answer from the options given below :

  1. (A) and (C) Only
  2. (C) and (D) Only
  3. (B), (C) and (E) Only
  4. (A), (C) and (D) Only

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