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Friday, 9 October

JEE Main 2020 · ChemistryMultiple choiceSingle correctMediumMulti-step

JEE Main 9 January 2020, Shift 2, Chemistry Q44

Question 44 of 75 in this shift, Chemistry question 19 of 25, Section A.

In the following reaction A is : A →(i) Br2,hν; (ii) KOH (alc.); (iii) O3; (iv) (CH3)2S; (v) NaOH (aq)+Δ\xrightarrow{\text{(i) } Br_2, h\nu;\ \text{(ii) KOH (alc.)};\ \text{(iii) } O_3;\ \text{(iv) } (CH_3)_2S;\ \text{(v) NaOH (aq)} + \Delta} cyclopent-1-ene-1-carbaldehyde

The figure, in words

Reaction scheme with five reagent steps (i) Br2, hv (ii) KOH (alc.) (iii) O3 (iv) (CH3)2S (v) NaOH (aq) + heat from A to a cyclopentene ring bearing a CHO group on the double-bond carbon.
  1. (1)[figure: methylcyclopentane]
  2. (2)[figure: cyclohexane]Official answer
  3. (3)[figure: ethylcyclopentane]
  4. (4)[figure: 1,2-dimethylcyclobutane (two methyl groups on adjacent ring carbons)]

Official answer

Option 2

NTA final key (Jan 2020).

Chapter
Aldehydes, Ketones and Carboxylic Acids
Topic
Aldol and Cannizzaro
Idea tested
Intramolecular Aldol

Same idea in other shifts

Asked 2× in all
  1. 8 Apr 2025, Shift 2 · Q68When [structure: CH3C(=O)CH2CH2CH2CH2CHO\mathrm{CH_3C(=O)CH_2CH_2CH_2CH_2CHO}, a skeletal zigzag chain with a methyl ketone at one end and an aldehyde (C=O…MediumSingle correctHas a figure

Question text from the official JEE Main paper published by NTA; answer from the final answer key. Chapter, topic and idea tags, difficulty and skill are Lumi’s. This question needs a figure we do not reproduce; it is described in words above. Lumi analyses 42 of the 174 JEE Main shifts held from 2017 to 2026.