A compound with molecular mass 180 is acylated with `CH_3 COCl` to get a compound with molecular mass 390. The number of amino groups present per molecule of the former compound is

Answer

5

Explanation

During acetylation, one H atom (at mass=1 amu) of the `NH_2` group is replaced by an acetyl group, i.e.,
`CH_3 CO ` (mol. Mass = 43 amu) -`NH_2 + CH_3 COCl to - NHCOCH_2 + HCl`
In other words, acetylation of each `NH_2` group increases the mass by 43-1 -42 amu. Now since the mol, mass of the organic compound is 180 while that of the acetylated product is 390, therefore, increase in the mass due to acetylation `=390-180=210` amu.
`therefore` No. of `-NH_2` groups `=(210)/(42) = 5`