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GATE 2025 CY – Question 52

Organic Chemistry · Reaction Mechanisms: Basic mechanistic concepts and energy profile diagrams - kinetics versus thermodynamic control, Hammond’s postulate and Curtin-Hammett principle. Methods of determining reaction mechanisms through kinetics, identification of products, intermediates and isotopic labelling. Solvent effects in substitution and elimination reactions. Linear free-energy relationship – Hammett and Taft equations. · 2 marks · Multiple select

Consider the following two reactions and their corresponding Hammett plots. Choose the option(s) that correctly match(es) the points on the graph given in Column-I with substituents X given in Column-II in accordance with their substituents constant $\sigma$.

Column-I (points on the graph)Column-II (substituent X)
pNH2
qNO2
rOMe
sCl
tMe
uCN
Two reactions and Hammett plots with labeled points p–u and substituent table.
  1. Option A in the figure
  2. Option B in the figure
  3. Option C in the figure
  4. Option D in the figure

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Show answer and explanation

Correct answer: (A) Option A in the figure; (C) Option C in the figure

Explanation

The sigma order is NH2 < OMe < Me < 0 < Cl < CN < NO2. Hence u is NH2, t is OMe, p is Me, s is Cl, q is CN and r is NO2, which satisfies every pair in A and C.