P a g e | 1
The main purpose of the laboratory experiment was to identify the unknown organic
compound which contains carbon, oxygen, nitrogen, chlorine, bromine, nitrogen or fluorine
from a given set of data that was obtained through mass spectrometry of the compound . A
mass spectrum can be used to confirm or find the identity of a chemical species. A mass
spectrum is made by a mass spectrometer which separates particles based on mass . When the
gaseous sample is let in through the inlet of the spectrometer, it is bombarded with electrons .
When one electron hits a molecule of the sample, an electron is deflected off of the molecule.
This is shown by the following reaction.
Since the molecule is now missing an electron it is unstable, and so it yields fragments which
can be summarized in the following equations.
After ionization and fragmentation, the particles are accelerated so they all move along a path
that goes between two electromagnetic plates in order to become separated . The 3
electromagnetic field separates the ions based on the intensity of the charge possessed by each
fragment. This means larger fragments are deflected much further than smaller ones since
mass is proportional to charge . Thus the ions are separated by mass, and the ones that reach
the detector are detected electrically and the result is displayed on a stick diagram . P a g e | 2
Refer to Lab Manual
The given data for the unknown compound resulted in the following graph
Mass spectrometry analysis for Unknown # 20
Relative Abundance M+
13 15 25 27 35 37 47 49 51 60 62 64 66 72 83 85 87 96 98 100 102
Mass/Charge (in amu/electron charge)
Figure -1 : The given data was converted into a graph in order to identify the M+ and the base
peak in order to compare it to other peaks.
Calculations and Inferences
From Figure-1, the base peak, which has a relative abundance of 100%, was found at a
mass/charge value of 63. This means the most stable fragment from the main compound has a
molecular mass of of about 63.
The following table illustrates the possible fragments and their relation to M+ ion P a g e | 3
Table-1: Tabulated data from mass spectrometry and possible fragments for unknown # 20
Column-1 Column-2 Column-4
Amu of peak Relation to M Possible fragment
loss from M
102 M + 4
100 M + 2
98 M + Molecular Ion
97 M – 1 Loss of 1 H
87 M – 11
85 M – 13
84 M –1 4
83 M – 15 CH 3 CHCl2
65 M – 33 Loss of a Cl
64 M – 34
63 M – 35 Base Peak Loss of a Cl
62 M – 36 C2H 3l
61 M – 37 C H Cl+
60 M – 38 C 2Cl , C2H 3 Cl
49 M – 49
48 M – 50
47 M – 51 CH 4l+
27 M – 71 C2H3
26 M – 72 C2H 2
25 M – 73 C2H
By analyzing the given data, the M+ ion was found to be at 98 amu since it has the highest peak
along with the largest mass number. Since the M+ peak is accompanied by two smaller peaks
along its side, the rule for the presence of halogens was applied to check for halogen atoms.
C HECK FOR H ALOGENS :
Upon further examination, the following trend was observed
M - 35 : M - 37
100 : 32.5
3 : 1 P a g e | 4
The ratio of 3 : 1 suggests that atleast one chlorine atom is present in the unknown molecule.
To confirm the number of chlorine atoms, the ratios of M+, M+2, M+4 were