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Saturday, 31 October

JEE Main 2024 · ChemistryMultiple choiceOtherEasyApplication

JEE Main 30 January 2024, Shift 1, Chemistry Q72

Question 72 of 90 in this shift, Chemistry question 12 of 30, Section A.

Compound A formed in the following reaction reacts with B gives the product C. Find out A and B. CH3−C≡CH+Na⟶A→BCH3−C≡C−CH2−CH2+NaBr\mathrm{CH_3-C\equiv CH + Na \longrightarrow A \xrightarrow{B} CH_3-C\equiv C-CH_2-CH_2 + NaBr} (C) with a CH3\mathrm{CH_3} group drawn below the last CH2\mathrm{CH_2} (i.e. CH3−C≡C−CH2−CH2−CH3\mathrm{CH_3-C\equiv C-CH_2-CH_2-CH_3})

The figure, in words

Reaction scheme: propyne + Na gives A; A with B gives product C = CH3-C≡C-CH2-CH2 with a CH3 drawn below the last CH2 (pent-2-yne chain, i.e. hex-2-yne), plus NaBr.
  1. (1)A=CH3−C≡C−Na+, B=CH3−CH2−CH2−Br\mathrm{A = CH_3-C\equiv \overset{-}{C}\overset{+}{Na},\ B = CH_3-CH_2-CH_2-Br}Official answer
  2. (2)A=CH3−C≡C−Na+, B=CH3−CH2−CH3\mathrm{A = CH_3-C\equiv \overset{-}{C}\overset{+}{Na},\ B = CH_3-CH_2-CH_3}
  3. (3)A=CH3−CH2−CH3, B=CH3−C≡CH\mathrm{A = CH_3-CH_2-CH_3,\ B = CH_3-C\equiv CH}
  4. (4)A=CH3−CH=CH2, B=CH3−CH2−CH2−Br\mathrm{A = CH_3-CH=CH_2,\ B = CH_3-CH_2-CH_2-Br}

Official answer

Option 1

NTA final key.

Chapter
Hydrocarbons
Topic
Alkenes and Alkynes
Idea tested
Acetylide Ion Alkylation

Same idea in other shifts

Asked 2× in all
  1. 27 Aug 2021, Shift 1 · Q42In the following sequence of reactions, the final product D is : CH3−C≡C−H+NaNH2→A\mathrm{CH_3-C\equiv C-H + NaNH_2} \rightarrow \mathrm{A} A\mathrm{A}…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.