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:

A hydroxy compound with molar mass 122 g mol−1 is acetylated with acetic anhydride and product has molar mass 290 g mol−1

Q. 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:

(A) 2

(B) 4

(D) 5

Correct Answer: 4

Explanation

Acetylation of one hydroxyl (–OH) group replaces the hydrogen atom by an acetyl group (–COCH₃).

Increase in molar mass per hydroxyl group during acetylation is:

\[ \text{Mass of } (-\mathrm{COCH_3}) - \text{Mass of H} = 43 - 1 = 42 \, \text{g mol}^{-1} \]

Given molar mass of compound (X):

\[ M_X = 122 \, \text{g mol}^{-1} \]

Molar mass of acetylated product:

\[ M_{\text{product}} = 290 \, \text{g mol}^{-1} \]

Increase in molar mass after acetylation:

\[ \Delta M = 290 - 122 = 168 \, \text{g mol}^{-1} \]

If number of hydroxyl groups is \( n \), then:

\[ 42n = 168 \]

\[ n = 4 \]

Therefore, compound (X) contains four hydroxyl groups.

Explanation

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