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Saturday, 31 October

JEE Main 2024 · ChemistryMultiple choiceDiagram basedMediumMulti-step

JEE Main 5 April 2024, Shift 2, Chemistry Q75

Question 75 of 90 in this shift, Chemistry question 15 of 30, Section A.

Identify A and B in the given chemical reaction sequence : Benzene + succinic anhydride (cyclic five-membered anhydride) →AlCl3\xrightarrow{\mathrm{AlCl_3}} A →HClZn−Hg\xrightarrow[\mathrm{HCl}]{\mathrm{Zn-Hg}} B →H+\xrightarrow{\mathrm{H^+}} [benzene ring fused to a six-membered ring carrying C=O]

The figure, in words

Reaction scheme: benzene (drawn as a ring) reacts with succinic anhydride (five-membered cyclic anhydride) in presence of AlCl3\mathrm{AlCl_3} to give A; A with Zn-Hg/HCl gives B; B with H+\mathrm{H^+} gives a fused bicyclic product: benzene ring fused to a six-membered ring with a C=O (1-tetralone). Options are structure pairs: (1) A = aryl ketone acid Ar−CO−CH2CH2−COOH\mathrm{Ar-CO-CH_2CH_2-COOH}, B = Ar−CH2CH2CH2−COOH\mathrm{Ar-CH_2CH_2CH_2-COOH}; (2) A = Ar−CH2CH2CH2−COOH\mathrm{Ar-CH_2CH_2CH_2-COOH} (drawn with COOH at chain end), B = Ar−(CH2)3−CH2OH\mathrm{Ar-(CH_2)_3-CH_2OH}; (3) A = tetralin-1,4-dione, B = tetralin-1,4-diol; (4) A = tetralin-1,4-dione, B = a dihydronaphthalene (benzene fused with ring containing one double bond).
  1. (1)A - C6H5−CO−CH2CH2−COOH\mathrm{C_6H_5-CO-CH_2CH_2-COOH}, B - C6H5−CH2CH2CH2−COOH\mathrm{C_6H_5-CH_2CH_2CH_2-COOH}Official answer
  2. (2)A - C6H5−CH2CH2CH2−COOH\mathrm{C_6H_5-CH_2CH_2CH_2-COOH}, B - C6H5−CH2CH2CH2−CH2OH\mathrm{C_6H_5-CH_2CH_2CH_2-CH_2OH}
  3. (3)A - 1,4-dioxo-tetralin (naphthalene-1,4-dione fused ring, C=O at both positions 1 and 4), B - the corresponding 1,4-diol (OH at positions 1 and 4)
  4. (4)A - 1,4-dioxo-tetralin (C=O at both positions 1 and 4), B - bicyclic fused benzene ring with one C=C in the second ring

Official answer

Option 1

NTA final key.

Chapter
Hydrocarbons
Topic
Aromatic Hydrocarbons
Idea tested
Friedel-Crafts Acylation and Acylium Ion

Same idea in other shifts

Asked 4× in all
  1. 4 Apr 2024, Shift 1 · Q89The number of the correct reaction(s) among the following is ________. (A) [benzene + benzoyl chloride (C6H5COCl\mathrm{C_6H_5COCl}),…MediumNumerical valueHas a figure
  2. 31 Jan 2024, Shift 2 · Q77Identify major product 'P' formed in the following reaction. [reaction: benzene + benzoyl chloride (C6_6H5_5COCl) --(Anhydrous…EasyDiagram basedHas a figure
  3. 31 Aug 2021, Shift 2 · Q45The structures of A and B formed in the following reaction are : [Ph = −C6H5-\mathrm{C_6H_5}] [benzene ring (with inner circle) + 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.