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EEJ MAIN Chemistry QUESTION #7514
Question 1

A compound with molecular mass 180 is acylated with CH$_3$COCl to yield a compound with molecular mass 390. How many amino ($-\text{NH}_2$) groups does the original compound contain?

  • 2
  • 5✔️
  • 4
  • 6
Correct Answer Explanation

Acylation: each $-\text{NH}_2$ reacts with CH$_3$COCl to introduce a $-\text{COCH}_3$ group ($M = 42$) and release HCl.

Net mass added per amino group $= 42 - 1 = 42$ (the $-H$ is replaced by $-\text{COCH}_3$)

Wait — each NH$_2$ + CH$_3$COCl → NH$\cdot$COCH$_3$ + HCl. Mass change per group $= 42 - 1 = +41$... more precisely: $-NH_2$ (16) becomes $-NHCOCH_3$ (58): increase = 42.

Increase in mass $= 390 - 180 = 210$

Number of amino groups $= \dfrac{210}{42} = \mathbf{5}$