Learn

Friday, 9 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 3× 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

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.