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Saturday, 31 October

JEE Main 2021 · ChemistryMultiple choiceSingle correctEasyConceptual

JEE Main 17 March 2021, Shift 2, Chemistry Q45

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

Choose the correct statement regarding the formation of carbocations A and B given. CH3−CH2−CH=CH2+HBr\mathrm{CH_3-CH_2-CH=CH_2 + HBr} gives two branches: CH3−CH2−CH2−C+H2+Br−\mathrm{CH_3-CH_2-CH_2-\overset{+}{C}H_2 + Br^-} "A" CH3−CH2−C+H−CH3+Br−\mathrm{CH_3-CH_2-\overset{+}{C}H-CH_3 + Br^-} "B"

The figure, in words

Reaction scheme: CH3-CH2-CH=CH2 + HBr with an arrow splitting into two branches; upper branch gives CH3-CH2-CH2-CH2(+) + Br(-) labelled "A", lower branch gives CH3-CH2-CH(+)-CH3 + Br(-) labelled "B". Plus signs drawn above the charged carbons.
  1. (1)Carbocation A is more stable and formed relatively at slow rate
  2. (2)Carbocation B is more stable and formed relatively at slow rate
  3. (3)Carbocation A is more stable and formed relatively at faster rate
  4. (4)Carbocation B is more stable and formed relatively at faster rateOfficial answer

Official answer

Option 4

NTA final key.

Chapter
Hydrocarbons
Topic
Alkenes and Alkynes
Idea tested
Markovnikov's Rule Application

Same idea in other shifts

Asked 13× in all
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  3. 4 Apr 2024, Shift 1 · Q77Identify the correct set of reagents or reaction conditions 'X' and 'Y' in the following set of transformation.…EasyOther
  4. 31 Jan 2024, Shift 1 · Q76The product (C) in the below mentioned reaction is :…EasySingle correct
  5. 31 Jan 2024, Shift 2 · Q75Major product of the following reaction is -HardDiagram basedHas a figure
  6. 25 Jul 2022, Shift 2 · Q73Major product of the following reaction is [figure: skeletal drawing, left to right: a C=C double bond at the left end whose inner carbon…MediumDiagram basedHas a figure
  7. 24 Jun 2022, Shift 1 · Q90The major product 'A' of the following given reaction has ______ sp2sp^2 hybridized carbon atoms. 2,7-Dimethyl-2,6-octadiene…HardNumerical value
  8. 25 Jun 2022, Shift 1 · Q73The product formed in the following reaction. [figure: (CH3)2C=CH2\mathrm{(CH_3)_2C{=}CH_2} drawn with two CH3\mathrm{CH_3} on the left carbon and…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.