A compound with molecular mass 180 is acylated with CH_3COCl to g…

MCQ

A compound with molecular mass $180$ is acylated with $CH_3COCl$ to get a compound with molecular mass $390.$ The number of amino groups present per molecule of the former compound is :

A
$2$
✓
$5$
C
$4$
D
$6$

✓

Answer

Correct option: B.

$5$

b
During acetylation, one $H$ atom with atomic mass $1\,amu$ of $- NH_2$ group is replaced by an acetyl group $\mathrm{CH}_{3} \mathrm{CO}[\text { molecular mass }=434 \,\mu ]$. Thus

$-\mathrm{NH}_{2}+\mathrm{CH}_{3} \mathrm{COCl} \longrightarrow-\mathrm{NHCOCH}_{3}+\mathrm{HCl}$

The above equation suggests that, the acylation of each $-\mathrm{NH}_{2}$ group increases the mass by $42 \,\mu$ $[43-1] .$ If the molecular mass of the organic compound is $180 \,\mu$ while that of the acylated product is $390 \,\mu$, then the increase in the mass due to acylation is given by

$390-180=210 \,\mu$

Hence, the number of $-\mathrm{NH}_{2}$ groups $=\frac{210\, \mu}{42\, \mu}=5$