Introduction to Mass Spectrometry
Following are examples of compounds listed
by functional group, which demonstrate patterns which can be seen in mass
spectra of compounds ionized by electron impact ionization. These
examples do not provide information about the fragmentation mechanisms
that cause these patterns. Additional information can be found in
mass spectrometry reference books.
this page, or use this list to move to select functional groups (QUIZ!
links you to a tutorial quiz for that functional group):
An alcohol's molecular ion is small or non-existent.
Cleavage of the C-C bond next to the oxygen usually occurs. A loss
of H2O may occur as in the spectra below.
MW = 88.15
Cleavage of bonds next to the carboxyl group
results in the loss of hydrogen (molecular ion less 1) or the loss of CHO
(molecular ion less 29).
MW = 132.16
Molecular ion peaks are present, possibly
with low intensity. The fragmentation pattern contains clusters of
peaks 14 mass units apart (which represent loss of (CH2)nCH3).
Primary amides show a base peak due to the
MW = 101.15
Molecular ion peak is an odd number.
Alpha-cleavage dominates aliphatic amines.
MW = 73.13
Another example is a secondary amine shown
below. Again, the molecular ion peak is an odd number. The
base peak is from the C-C cleavage adjacent to the C-N bond.
MW = 121.18
Molecular ion peaks are strong due to the
MW = 128.17
In short chain acids, peaks due to the loss
of OH (molecular ion less 17) and COOH (molecular ion less 45) are prominent
due to cleavage of bonds next to C=O.
MW = 86.09
Fragments appear due to bond cleavage next
to C=O (alkoxy group loss, -OR) and hydrogen rearrangements.
MW = 88.11
Fragmentation tends to occur alpha to the oxygen atom (C-C bond next to the oxygen).
Ethyl methyl ether
MW = 60.10
The presence of chlorine or bromine atoms
is usually recognizable from isotopic peaks.
MW = 123.00
Major fragmentation peaks result from cleavage
of the C-C bonds adjacent to the carbonyl.
MW = 114.19
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