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Saturday, 31 October

JEE Main 2021 · ChemistryMultiple choiceDiagram basedMediumMulti-step

JEE Main 25 July 2021, Shift 2, Chemistry Q45

Question 45 of 90 in this shift, Chemistry question 15 of 30, Section A.

[reaction scheme] drawn structure: label Br joined to a bend, then label CHO; with reagent EtOH excess / dry HCl gas gives "A" (major product); "A" with reagent tBuO−K+\mathrm{{}^tBuO^{-}K^{+}} gives "B" (major product) [where Et ⇒−C2H5\Rightarrow -\mathrm{C_2H_5} tBu⇒(CH3)3C−{}^tBu \Rightarrow (\mathrm{CH_3})_3\mathrm{C}-] Consider the above reaction sequence, Product "A" and Product "B" formed respectively are :

The figure, in words

Reaction scheme with reagents printed above and below arrows; each option shows two drawn structures separated by a comma (first = A, second = B).
  1. (1)[figure: first structure: label EtO joined to a bend which joins label CHO; second structure: label EtO joined to a bend, then to a carbon bearing label Ot^tBu (upper right) and label OH (below)]
  2. (2)[figure: first structure: label Br joined to a bend, then to a carbon bearing OEt (upper right) and OEt (below); second structure: label H2_2C double-bonded to a carbon bearing OEt (upper right) and OEt (below)]Official answer
  3. (3)[figure: first structure: label Br joined to a bend, then to a carbon bearing OEt (upper right) and OEt (below); second structure: label t^tBuO joined to a bend, then to a carbon bearing OEt (upper right) and OEt (below)]
  4. (4)[figure: first structure: label EtO joined to a bend, then to a carbon bearing OEt (upper right) and OEt (below); second structure: label H2_2C double-bonded to a carbon bearing OEt (upper right) and OEt (below)]

Official answer

Option 2

NTA final key.

Chapter
Aldehydes, Ketones and Carboxylic Acids
Topic
Nucleophilic Addition
Idea tested
Acetal and Ketal Formation

Same topic in other shifts

All Nucleophilic Addition questions
  1. 2 Apr 2026, Shift 2 · Q67A molecule (X) with following structure under mild acidic condition is hydrolysed to produce (Y) and (Z). Identify the correct statements…MediumSingle correct
  2. 5 Apr 2026, Shift 2 · Q66Given below are two statements : Statement I : The condensation reaction between CH3−CH=O\mathrm{CH_3-CH=O} and H2N−NH−C(=O)−NH2\mathrm{H_2N-NH-C(=O)-NH_2}…MediumTwo statements
  3. 7 Apr 2025, Shift 2 · Q68"P" is an optically active compound with molecular formula C6H12O\mathrm{C_6H_{12}O}. When 'P' is treated with 2, 4-dinitrophenylhydrazine, it…MediumDiagram basedHas a figure
  4. 6 Apr 2024, Shift 1 · Q79Which among the following aldehydes is most reactive towards nucleophilic addition reactions?EasySingle correctHas a figure
  5. 6 Apr 2024, Shift 2 · Q78Consider the given reaction, identify the major product P. CH3−COOH\mathrm{CH_3-COOH}…MediumSingle correct
  6. 30 Jan 2024, Shift 1 · Q90The compound formed by the reaction of ethanal with semicarbazide contains ________ number of nitrogen atoms.EasyNumerical value

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.