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Saturday, 31 October

JEE Main 2020 · ChemistryMultiple choiceSingle correctHardApplication

JEE Main 2 September 2020, Shift 2, Chemistry Q44

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

The major product obtained from E2\mathrm{E_2}-elimination of 3-bromo-2-fluoropentane is :

The figure, in words

Options are drawn condensed structural formulas: in option 1 the Br is printed above the CH; in option 2 the CH3 is printed below the carbon that bears F on its right; in option 3 the Br is printed above the carbon; in option 4 the F is printed above the CH.
  1. (1)CH3CH2−CH(Br)−CH=CH2\mathrm{CH_3CH_2-CH(Br)-CH=CH_2}
  2. (2)CH3CH2CH=C(CH3)−F\mathrm{CH_3CH_2CH=C(CH_3)-F}Official answer
  3. (3)CH3−CH2−C(Br)=CH−CH3\mathrm{CH_3-CH_2-C(Br)=CH-CH_3}
  4. (4)CH3−CH=CH−CH(F)−CH3\mathrm{CH_3-CH=CH-CH(F)-CH_3}

Official answer

Option 2

NTA final key (Sep 2020).

Chapter
Haloalkanes and Haloarenes
Topic
Alkenes and Alkynes
Idea tested
Saytzeff vs. Hofmann Elimination

Same idea in other shifts

Asked 7× in all
  1. 2 Apr 2025, Shift 2 · Q75Consider the above sequence of reactions. 151 g of 2-bromopentane is made to react. Yield of major product P is 80% whereas Q is 100%.…MediumNumerical valueHas a figure
  2. 5 Apr 2024, Shift 2 · Q77Identify the major product in the following reaction. 1-bromo-1-methylcyclopentane…EasyDiagram basedHas a figure
  3. 25 Jun 2022, Shift 1 · Q75The major product in the reaction [figure: CH3−C(CH3)(CH3)−Cl\mathrm{CH_3-C(CH_3)(CH_3)-Cl} (central C with CH3\mathrm{CH_3} above, CH3\mathrm{CH_3} below,…EasySingle correctHas a figure
  4. 31 Aug 2021, Shift 2 · Q41The major product of the following reaction is : [reaction: starting material drawn as a five-membered ring; reagent above/below arrow:…MediumDiagram basedHas a figure
  5. 2 Apr 2017 (offline) · Q52Which of the following, upon treatment with *tert*-BuONa followed by addition of bromine water, fails to decolourize the colour of bromine ?HardSingle correctHas a figure
  6. 2 Apr 2017 (offline) · Q56The major product obtained in the following reaction is : [reaction: (+)-C6H5CH(Br)CH2C6H5\mathrm{C_6H_5CH(Br)CH_2C_6H_5} (Br on wedge, H on hash at the…MediumSingle correctHas 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.