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Saturday, 31 October

JEE Main 2024 · ChemistryMultiple choiceSingle correctMediumConceptual

JEE Main 9 April 2024, Shift 1, Chemistry Q71

Question 71 of 90 in this shift, Chemistry question 11 of 30, Section A.

Relative stability of the contributing structures is : (I) CH2=CH−C∥O¨:−H\mathrm{CH_2=CH-\overset{\ddot{O}:}{\overset{\|}{C}}-H} ⟷\longleftrightarrow (II) +CH2−CH=C(−O¨:−)−H\mathrm{{}^+CH_2-CH=C(-\ddot{O}:^-)-H} ⟷\longleftrightarrow (III) −:CH2−CH=C(−O¨+:)−H\mathrm{{}^-{:}CH_2-CH=C(-\ddot{O}^+{:})-H}

The figure, in words

Three resonance contributors of acrolein (CH2=CH-CHO) with lone pairs shown: (I) CH2=CH-C(=O:)-H neutral; (II) +CH2-CH=C(-O:-)-H, i.e. positive charge on terminal CH2 and negative on oxygen; (III) -:CH2-CH=C(-O+:)-H, i.e. negative charge on terminal CH2 carbon and positive on oxygen.
  1. (1)(III) > (II) > (I)
  2. (2)(II) > (I) > (III)
  3. (3)(I) > (III) > (II)
  4. (4)(I) > (II) > (III)Official answer

Official answer

Option 4

NTA final key.

Chapter
Organic Chemistry: Some Basic Principles and Techniques
Topic
Resonance and Hyperconjugation
Idea tested
Relative Stability

Same idea in other shifts

Asked 4× in all
  1. 9 Apr 2024, Shift 2 · Q73The correct stability order of the following resonance structures of CH3−CH=CH−CHO\mathrm{CH_3-CH=CH-CHO} is I:…MediumSingle correctHas a figure
  2. 29 Jan 2024, Shift 1 · Q73The difference in energy between the actual structure and the lowest energy resonance structure for the given compound isEasySingle correct
  3. 29 Jun 2022, Shift 2 · Q73Which of the following carbocations is most stable?MediumDiagram basedHas 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 108 of the 174 JEE Main shifts held from 2017 to 2026.