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Friday, 9 October

JEE Main 2020 · ChemistryMultiple choiceSingle correctMediumMulti-step

JEE Main 6 September 2020, Shift 2, Chemistry Q30

Question 30 of 75 in this shift, Chemistry question 5 of 25.

The increasing order of the boiling points of the major products A, B and C of the following reactions will be : (a) [figure: but-1-ene, CH2=CH−CH2−CH3\mathrm{CH_2=CH-CH_2-CH_3}] + HBr, (C6H5CO)2\mathrm{(C_6H_5CO)_2} (benzoyl peroxide) →\to A (b) [figure: 2-methylpropene, (CH3)2C=CH2\mathrm{(CH_3)_2C=CH_2}] + HBr →\to B (c) [figure: but-2-ene, CH3−CH=CH−CH3\mathrm{CH_3-CH=CH-CH_3}] + HBr →\to C

The figure, in words

Three reactions drawn as skeletal structures: (a) terminal alkene (but-1-ene) + HBr with benzoyl peroxide -> A; (b) 2-methylpropene + HBr -> B; (c) but-2-ene + HBr -> C
  1. (1)A<B<CA<B<C
  2. (2)B<C<AB<C<AOfficial answer
  3. (3)C<A<BC<A<B
  4. (4)A<C<BA<C<B

Official answer

Option 2

NTA final key (Sep 2020).

Chapter
Hydrocarbons
Topic
Alkenes and Alkynes
Idea tested
Peroxide Effect (Anti-Markovnikov)

Same idea in other shifts

Asked 2× in all
  1. 2 Apr 2017 (offline) · Q583-Methyl-pent-2-ene on reaction with HBr in presence of peroxide forms an addition product. The number of possible stereoisomers for the…MediumSingle 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.