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GATE 2021 CY – Question 11

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. · 1 mark · Multiple choice

The rates of alkaline hydrolysis of the compounds shown below follow the order:

Diagram for GATE 2021 CY question 11
  1. I > II > III
  2. II > I > III
  3. II > III > I
  4. III > I > II

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Correct answer: (C) II > III > I

Explanation

The bulky tert-butyl group strongly favours an equatorial position and fixes the dominant chair. In cis ester II, the ester is axial; in trans ester III it is equatorial. The axial acyl substituent is destabilized by steric interactions, increasing its hydrolysis rate relative to III. Amide I is much less reactive because nitrogen donation stabilizes its carbonyl and amide is a poor leaving group.

Thus **II>III>I, C**.