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Saturday, 31 October

JEE Main 2020 · ChemistryMultiple choiceDiagram basedHardMulti-step

JEE Main 4 September 2020, Shift 2, Chemistry Q44

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

The major product [R] in the following sequence of reactions is : HC≡CH→(ii) H3C↘CH−Br ↗(CH3)2CH(i) LiNH2/ether\mathrm{HC\equiv CH} \xrightarrow[\text{(ii) } \mathrm{H_3C}\searrow\mathrm{CH-Br}\ \nearrow(\mathrm{CH_3})_2\mathrm{CH}]{\text{(i) } \mathrm{LiNH_2/ether}} [P] →(ii) NaBH4(i) HgSO4/H2SO4\xrightarrow[\text{(ii) } \mathrm{NaBH_4}]{\text{(i) } \mathrm{HgSO_4/H_2SO_4}} [Q] →ΔConc. H2SO4\xrightarrow[\Delta]{\mathrm{Conc.\ H_2SO_4}} [R]

The figure, in words

Stem is a reaction scheme: the second reagent in step (ii) of the first arrow is drawn as H3C and (CH3)2CH branches on a CH bonded to Br. Options are drawn structures with bonds drawn at angles from the central carbon.
  1. (1)[figure: H3C\mathrm{H_3C} and (CH3)2CH(\mathrm{CH_3})_2\mathrm{CH} both bonded to a carbon that is double-bonded to CH−CH3\mathrm{CH-CH_3}; drawn as C=CH−CH3\mathrm{C=CH-CH_3}]
  2. (2)[figure: H2C\mathrm{H_2C} double-bonded to a carbon which carries −CH2−CH3\mathrm{-CH_2-CH_3} and CH(CH3)2\mathrm{CH(CH_3)_2}]
  3. (3)[figure: H3C\mathrm{H_3C} and H3CCH2\mathrm{H_3CCH_2} both bonded to a carbon that is double-bonded to C(CH3)2\mathrm{C(CH_3)_2}]Official answer
  4. (4)[figure: H3C\mathrm{H_3C} and (CH3)2CH(\mathrm{CH_3})_2\mathrm{CH} both bonded to a CH\mathrm{CH} which is bonded to CH=CH2\mathrm{CH=CH_2}]

Official answer

Option 3

NTA final key (Sep 2020).

Chapter
Hydrocarbons
Topic
Alkenes and Alkynes
Idea tested
Alkylation of Terminal Alkynes

Same idea in other shifts

Asked 2× in all
  1. 27 Jun 2022, Shift 2 · Q73What will be the major product of following sequence of reactions? n−Bu−\mathrm{n-Bu-}[drawn: terminal triple bond]…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.