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Interpreting the mass
spectrum of methoxyethane
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Brown's Chemistry Advanced Level Pre-University Chemistry Revision Study
Notes for UK IB KS5 A/AS GCE advanced A level organic chemistry students US
K12 grade 11 grade 12 organic chemistry courses involving molecular
spectroscopy analysing mass spectra of methoxyethane
See also
comparing the infrared, mass, 1H NMR and 13C NMR
spectra of the 3 isomers of C3H8O
Methoxyethane
Interpreting the fragmentation pattern of the mass spectrum of methoxyethane
[M]+ is the molecular ion peak (M) with an m/z of
60 corresponding to [C3H8O]+, the original methoxyethane molecule minus an electron,
[CH3OCH2CH3]+.
The small M+1 peak at m/z 61, corresponds to an ionised
methoxyethane
molecule with one 13C atom in it i.e. an ionised methoxyethane molecule of
formula [13C12C2H8O]+
Carbon-13 only accounts for ~1% of all carbon atoms
(12C ~99%), but the more carbon atoms in the molecule,
the greater the probability of observing this 13C M+1
peak.
Methoxyethane has 3 carbon atoms, so on
average, ~1 in 33 molecules will contain a 13C atom.
In the mass spectrum of ethers, an M+1 ion can also
be formed by a hydrogen atom radical combining with the molecular
ion i.e. m/z 61 can originate from [M]+ + H• ===>
[•MH]+
The most abundant ion of the molecule under mass
spectrometry investigation (methoxyethane) is usually given an arbitrary abundance value of
100, called the base ion peak, and all other abundances
('intensities') are measured against it.
Identifying the species giving the most prominent peaks
(apart from M) in the fragmentation pattern of methoxyethane.
Unless otherwise indicated, assume the carbon atoms in
methoxyethane are the 12C isotope.
Some of the possible positive ions, [molecular fragment]+,
formed in the mass spectrometry of methoxyethane.
| m/z value of
[fragment]+ |
59 |
45 |
43 |
31 |
29 |
28 |
27 |
15 |
| [molecular fragment]+ |
[C3H7O]+ |
[C2H5O]+ |
[C2H3O]+ |
[CH3O]+ |
[CH3CH2]+ |
[C2H4]+ |
[C2H3]+ |
[CH3]+ |
Analysing and explaining the principal ions in the
fragmentation pattern of the mass spectrum of methoxyethane
Atomic masses: H = 1; C = 12; O = 16
Bond enthalpies kJ/mol: C-C = 348; C-H = 412;
C-O = 360
Examples of equations to explain some of the most abundant ion peaks of
the mass spectrum of methoxyethane
Formation of m/z 59 ion:
[CH3OCH2CH3]+ ===> [C3H7O]+
+ H
C-H bond scission and expulsion of a proton (mass
change 60 - 1 = 59) from the parent molecular ion of methoxyethane.
Formation of m/z 45 ion:
[CH3OCH2CH3]+ ===> [C2H5O]+
+ CH3
Scission of a C-C or C-O bond to lose a methyl group
from the parent molecular ion (see also m/z 15).
Mass change: 60 - 15 = 45
The m/z 45 ion is the base peak ion, the most
abundant and 'stable' ion fragment for methoxyethane.
The m/z ion may have the structure CH3OCH2
or OCH2CH3 or ?
The m/z 45 ion could also be formed from C-C bond scission of the m/z 59 ion?
[C3H7O]+ ===> [C2H5O]+
+ CH2
Formation of m/z 43 ion:
[C3H7O]+ ===> [C2H3O]+
+ CH4
Scission of a C-C or C-O bond to lose a methane from
the m/z 59 ion ?
Mass change: 59 - 16 = 43
Formation of m/z 31 ion:
[CH3OCH2CH3]+ ===> [CH3O]+
+ CH2CH3
C-O bond scission of the parent molecular ion (see
also m/z 29 ion).
Mass change: 60 - 29 = 31
Formation of m/z 29 ion:
[CH3OCH2CH3]+ ===> [CH2CH3]+
+ CH3O
C-O bond scission of the parent molecular ion, mass change: 60 - 31 = 29.
The alternative ionisation to the formation of the
m/z 31 ion from the parent molecular ion of methoxyethane (above).
Formation of m/z 15 ion:
[CH3OCH2CH3]+ ===> [CH3]+
+ C2H5O
Scission of a C-C or C-O bond to lose a methyl
group from the parent molecular ion.
Mass change: 60 - 45 = 15
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Comparing the infrared, mass, 1H NMR and 13C NMR
spectra of the 3 isomers of C3H8O
NOTE: The images are linked to their
original detailed spectral analysis pages AND can be doubled in
size with touch screens to
increase the definition to the original propan-1-ol,
propan-2-ol and methoxyethane image sizes. |
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I wasn't able to obtain an infrared
spectrum for methoxyethane, so I've added the infrared spectrum
of ethoxyethane to enable a few comparisons with two aliphatic
alcohols
Comparing the
infrared
spectra of
propan-1-ol,
propan-2-ol and
methoxyethane
Propan-1-ol,
propan-2-ol and methoxyethane
are structural isomers of molecular formula C3H8O
Propan-1-ol,
propan-2-ol and methoxyethane
exemplify infrared spectra of the lower members of the homologous series
of aliphatic alcohols and ethers |
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INFRARED SPECTRA
(above): There are, as expected, differences in the fingerprint region at
wavenumbers 1500 to 400 cm-1, but most absorptions
for all three molecules are the various C-O and the many C-H
vibrational modes. However, there is one characteristic distinguishing
absorption only present in the infrared spectra of alcohols, but
not in ethers, that is the broad O-H stretching vibration
peaking at ~3350 cm-1. There is also another broad
absorption band (origin?) peaking at ~650 cm-1 in the
alcohol spectra, but not in the ether spectra. |
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Comparing the
mass
spectra of
propan-1-ol,
propan-2-ol and
methoxyethane
Propan-1-ol,
propan-2-ol and methoxyethane
are structural isomers of molecular formula C3H8O
Propan-1-ol,
propan-2-ol and methoxyethane
exemplify the mass spectra of the lower members of the homologous series
of aliphatic alcohols and ethers |
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MASS SPECTRA (above):
The base ion peaks are m/z 45 for propan-2-ol and methoxyethane,
but that of propan-1-ol is m/z 31. Many of the fragmentation
ions are common to all three spectra. The m/z 45 ion is peak is
much smaller in the propan-1-ol spectrum compared to the other
two. The relative height for the m/z 29 ion [C2H5]+
is much greater in the mass spectrum of methoxyethane compared
to the other two spectra. |
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Comparing the
1H proton NMR
spectra of
propan-1-ol,
propan-2-ol and
methoxyethane
Propan-1-ol,
propan-2-ol and methoxyethane
are structural isomers of molecular formula C3H8O
Propan-1-ol,
propan-2-ol and methoxyethane exemplify the 1H proton NMR spectra of
the lower members of the homologous series of aliphatic alcohols and
ethers |
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1H NMR SPECTRA (above): The 1H NMR spectra of
all three molecules give different integrated proton ratios for the
different 1H chemical environments i.e. the proton
ratios are as follows: propan-1-ol
3:2:2:1; propan-2-ol 6:1:1 and methoxyethane
3:2:3. Therefore, all three can be distinguished by their
1H NMR spectra. |
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Comparing the
carbon-13 NMR
spectra of
propan-1-ol,
propan-2-ol and
methoxyethane
Propan-1-ol,
propan-2-ol and methoxyethane
are structural isomers of molecular formula C3H8O
Propan-1-ol,
propan-2-ol and methoxyethane exemplify the carbon-13 NMR spectra of
members of the lower members of the homologous series of aliphatic
alcohols and ethers |
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13C NMR SPECTRA
(above): The
13C NMR spectra of propan-1-ol and methoxyethane show
three different 13C NMR chemical shifts, but
propan-2-ol can be distinguished from the other two by
exhibiting only two chemical shift lines. You would need other
spectral data to distinguish propan-1-ol and methoxyethane. |
Key words & phrases: C3H8O CH3OCH2CH3 image diagram on how to interpret and explain the mass spectrum of
methoxyethane m/z m/e base peaks, image and diagram of the mass spectrum of
methoxyethane, details of the mass spectroscopy of methoxyethane, low and high resolution mass
spectrum of methoxyethane, prominent m/z peaks in the mass spectrum of
methoxyethane, comparative
mass spectra of methoxyethane, the molecular ion peak in the mass spectrum of
methoxyethane,
analysing and understanding the fragmentation pattern of the mass spectrum
of methoxyethane, characteristic pattern of peaks in the mass spectrum of
methoxyethane, relative
abundance of mass ion peaks in the mass spectrum of methoxyethane, revising the mass
spectrum of methoxyethane, revision of mass spectroscopy of methoxyethane, most abundant ions in the
mass spectrum of methoxyethane, how to construct the mass spectrum diagram for abundance
of fragmentation ions in the mass spectrum of methoxyethane, how to analyse the mass
spectrum of methoxyethane, how to describe explain the formation of fragmented ions in the
mass spectra of methoxyethane equations for explaining the formation of the positive ions
in the fragmentation of the ionised molecule of methoxyethane recognising the
base ion peak of methoxyethane interpreting
interpretation the mass spectrum of methoxyethane
for ethyl methyl ether
spectrum of methoxyethane methyl ethyl ether
CH3CH2OCH3
isomer of
molecular formula C3H8O Stick diagram of the relative abundance
of ionised fragments in the fingerprint pattern of the mass spectrum of
methoxyethane. Table of the m/e m/z values and formula of the ionised fragments in the
mass spectrum of methoxyethane. The m/e m/z value of the molecular ion peak in the
mass spectrum of methoxyethane. The m/e m/z value of the base ion peak in the
mass spectrum of methoxyethane. Possible examples of equations showing the formation
of the ionised fragments in methoxyethane. Revision notes on the mass spectrum of
methoxyethane.
Matching and deducing the structure of the methoxyethane molecule from its mass
spectrum. Mass spectroscopy of
aliphatic ethers,
mass spectra of methoxyethane, an isomer of molecular formula
C3H8O
Links associated
with methoxyethane
Mass spectroscopy index
The
infrared spectrum of methoxyethane
The H-1
NMR spectrum of methoxyethane
The
C-13 NMR spectrum of methoxyethane
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