Question

identify the following compounds from their mass spectra and the data provided.

only 10.5 and 10.9

10:53 AM Tue Nov 19 100% Undergraduate Instrumental Analysis (PDFDrive.com) Done Identify the following compounds from their mass spectra and the data provided: 10.4 m/z 28 29 30 31 32 33 34 0.98 Relative abundance 6.3 64 3.8 100 66 0.14 10.5 m/z 14 15 19 31 32 34 35 Relative abundance 17 100 1.0 2.0 10 9.3 89 95 1.1 34 100 33 50 15 31 124 4l35 20 50 100 10 40 60 70 80 90 110 16 30

Answer 1

10.5 ) The molecular ion is 35.

The major fragmentation clusters are 15 and 34. Now the delta m for each major peak is determined.

Here the values is 34-15 =19.  

If the delta m value is greater than 16 mass units , then a hetero atom is present. Here the hetero atom is Fluorine.

Now the formula is calculated using the equation C_nH_2n+1X ;where X is hetero atom.

The atomic mass of carbon is 12 and hydrogen is 1, so equation becomes,

12n+(2n+1) =15

14n =14

n = 1

Therefore formula is CH₃F.

10.9) The major fragmentation clusters are 26,35,48,61,72,96.

Now the delta m for each peak is determined . These are 9,13,13,11,24 .

Here the hetero atom is oxygen and the molecule contains two oxygen atoms.

The formula is calculated using the equation C_nH_2n+1X .

12n +(2n+1) = 26

14n+1=26

14n =25

n=25/14 =1.78 =2

The molecular formula is CH₃COOH