JEE Main 2026 — Jan 24, Shift 1 — Chemistry solution

JEE Main2026Jan 24, Shift 1Chemistry

A hydroxy compound (X) with molar mass 122 g mol $^{- 1}$ 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 290 g mol $^{- 1}$ . The number of hydroxyl groups present in compound (X) is :

Solution

Each acetylation converts one $- O H$ to $- O C O C H_{3}$ , replacing an H ( $1$ amu) with an acetyl group ( $C O C H_{3}$ , $43$ amu) — a net gain of $42$ amu per hydroxyl.

Mass gain $= 290 - 122 = 168$ amu.

Number of $- O H$ groups $= \frac{168}{42} = 4$ .

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