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Question:

A compound with molecular mass 180 is acylated with CH3COCl to get a compound with molecular mass 390. The number of amino groups present per molecule of the former compound is:

6

2

5

4

Solution:

R−NH2+CH3−CO−Cl→R−NH−CO−CH3+HCl
The product formed here is R−NH−CO−CH3 and the initial compound was R−NH2
MW of NH2 is 16
Each CH3−CO additionally increases the molecular wt. by 58
58 = 42
Total increase in MW = 390−180 = 210
Then, number of NH2 groups = 210/42 = 5
Hence, the correct option is A.