Question

The decreasing order of ease of alkaline hydrolysis for the following esters in

(I) ethyl benzoate; (II) ethyl 4-chlorobenzoate; (III) ethyl 4-nitrobenzoate; (IV) ethyl 4-methoxybenzoate

• A. III > II > IV > I
• B. IV > II > III > I
• C. III > II > I > IV
• D. II > III > I > IV

Hint:

Alkaline hydrolysis is faster when the benzene ring carries electron-withdrawing groups (they increase the electrophilicity of C=O) and slower with electron-donating groups.

Answer 1

The Correct Option is C

Alkaline hydrolysis proceeds by nucleophilic attack of OH\(^-\) on the ester carbonyl carbon, forming a tetrahedral intermediate. Electron-withdrawing substituents stabilise this intermediate and make the carbonyl carbon more electrophilic, so hydrolysis is faster; electron-donating groups slow it down.
III: p-NO\(_2\) (strong \(-M, -I\)), fastest.
II: p-Cl (net electron withdrawing), next.
I: H, reference.
IV: p-OCH\(_3\) (strong \(+M\) donor), slowest.
Order: III > II > I > IV.
Answer: (3) III > II > I > IV