JEE Main 2026 — Alcohols Phenols and Ethers Question with Solution
JEE Main 2026 (24 January Shift 1)
Question
A hydroxy compound with molar mass is acetylated with acetic anhydride, using a large excess of the reagent ensuring complete acetylation of all hydroxyl groups. The product obtained has a molar mass of . The number of hydroxyl groups present in compound (X) is:
Choose an option
Show full solutionCorrect option: C
Correct answer
C4
Step-by-step explanation
In acetylation, each hydroxyl group reacts:
R-OH + (CH₃CO)₂O → R-O-CO-CH₃ + CH₃COOH.
Each -OH is converted to -OCOCH₃, resulting in a net mass increase of 42 g/mol per hydroxyl group (addition of acetyl group mass 43, removal of hydrogen mass 1).
Given: Original molar mass = 122 g/mol, Product molar mass = 290 g/mol
Total mass increase = 290 - 122 = 168 g/mol
Number of hydroxyl groups = 168 ÷ 42 = 4
R-OH + (CH₃CO)₂O → R-O-CO-CH₃ + CH₃COOH.
Each -OH is converted to -OCOCH₃, resulting in a net mass increase of 42 g/mol per hydroxyl group (addition of acetyl group mass 43, removal of hydrogen mass 1).
Given: Original molar mass = 122 g/mol, Product molar mass = 290 g/mol
Total mass increase = 290 - 122 = 168 g/mol
Number of hydroxyl groups = 168 ÷ 42 = 4
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This is a previous-year question from JEE Main 2026, covering the Alcohols Phenols and Ethers chapter of Chemistry. PrepSharp catalogues every PYQ from JEE Main with a verified answer key and step-by-step solution prepared by IIT alumni — so you can search by chapter, topic or year and revise efficiently.