GATE 2024 CY – Question 61

Organic Chemistry · Organic Synthesis: Synthesis, reactions, mechanisms and selectivity involving the following classes of compounds – alkenes, alkynes, arenes, alcohols, phenols, aldehydes, ketones, carboxylic acids, esters, nitriles, halides, nitro compounds, amines and amides. Uses of Mg, Li, Cu, B, Zn, P, S, Sn and Si based reagents in organic synthesis. Carbon-carbon bond formation through coupling reactions – Heck, Suzuki, Stille, Sonogashira, Negishi, Kumada, Hiyama, Tsuji-Trost reactions; olefin metathesis, McMurry coupling and Buchwald-Hartwig amination reactions. Baylis-Hillman, Henry, Ritter, Sakurai, Tebbe olefination, Pauson-Khand and Nazarov cyclization reactions. Concepts of multistep synthesis – retrosynthetic analysis, strategic disconnections, synthons and synthetic equivalents. Atom economy and green chemistry, Umpolung reactivity – formyl and acyl anion equivalents. Selectivity in organic synthesis – chemo-, regio- and stereoselectivity. Protection and deprotection of functional groups. Concepts of asymmetric synthesis – resolution (including enzymatic), desymmetrization and use of chiral auxiliaries, organocatalysis. Carbon-carbon and carbonheteroatom bond forming reactions through enolates (including boron enolates), enamines and silyl enol ethers. Stereoselective addition to C=O groups (Cram, Prelog and Felkin-Anh models). Asymmetric aldol reactions – Evans reaction and proline catalyzed reaction. · 2 marks · Numerical answer

In the given reaction sequence, the amount of R produced (in g) is ____. (Given: molar mass (in g mol-1) of H = 1, C = 12, N = 14, O = 16, and S = 32) (rounded off to two decimal places)

Benzene (7.8 g) undergoes sulfonation, alkaline fusion and nitration, in 80%, 75% and 50% yields.

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: 7.35 to 7.35

Explanation

Exhaustive sulfonation followed by alkaline fusion produces resorcinol; nitration gives styphnic acid with molar mass 245 g/mol. Benzene starts at $7.8/78=0.100$ mol, and the overall yield is $0.80(0.75)(0.50)=0.30$. Product mass is $0.100(0.30)(245)=7.35$ g. The stored answer had not been updated to match this already corrected derivation.

Official GATE 2024 answer key: https://gate2026.iitg.ac.in/doc/download/2024/CYFinalAnswerKey.pdf