Propose a molecular formula for a compound that exhibits the following peaks in

ID: 984966 • Letter: P

Question

Propose a molecular formula for a compound that exhibits the following peaks in
its mass spectrum:

(a) (M)+• at m/z = 72, relative height = 38.3% of base peak
(M+1)+• at m/z = 73, relative height = 1.7% of base peak

(b) (M)+• at m/z= 68, relative height = 100% (base peak)
(M+1)+• at m/z = 69, relative height = 4.3%

(d) (M)+• at m/z = 96, relative height = 19.0% of base peak
(M+1)+• at m/z = 97, relative height = 1.5% of base peak

Part a)

Let us take base peak as 100%

Then, 1.7% would be = (100/38.3) x 1.7 = 4.44%

Here, (M)+ at m/z = 72 and (M+1)+ at m/z = 73 suggest Molecular weight of 72

Also, number of C atoms in the molecule = 4.44/1.1 = 4

Therefore, the molecular formula for a compound is C4H8O

Part b)

Here, base peak intensity =100%

(M)+ at m/z = 68 and (M+1)+ at m/z = 69 suggest Molecular weight of 68

Number of C atoms in the molecule = 4.3/1.1 = 3.9 (Less than 4, therefore take 3)

Therefore, the molecular formula for a compound is C3H4N2

Part c)

Here, base peak intensity = 100%

(M)+ at m/z = 54 and (M+1)+ at m/z = 55 suggest Molecular weight of 54

Number of C atoms in the molecule = 4.6/1.1 = 4

Therefore, the molecular formula for a compound is C4H6

Part d)

Let us take base peak as 100%

Then, 1.5% would be = (100/19) x 1.5 = 7.89%

Number of C atoms in the molecule = 7.89/1.1 = 7

Here, (M)+ at m/z = 96 and (M+1)+ at m/z = 97 suggest Molecular weight of 96

Therefore, the molecular formula for a compound is C7H12

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