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Interpreting
and explaining the mass
spectrum of 1,4-dioxane
[Author
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Dr Phil Brown PhD:
Doc Brown's advanced level organic chemistry exam revision notes
suitable for students of UK A level chemistry courses & US K12 grade
11, grade 12 and AP honors chemistry courses: Molecular
spectrometry - analysing the mass spectra of 1,4-dioxane
[spectra page updated
April 3rd 2026 *]
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mass spectrum of 1,4-dioxane
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Mass spectrometry - spectra index
Introductory note on the mass spectrum of 1,4-dioxane
Students and teachers please note
my explanation of the mass spectrum of 1,4-dioxane is designed for
advanced, but pre-university, chemistry courses.
If M represents the
1,4-dioxane molecule, the initial ionisation to give the molecular ion is:
M(g) +
high KE e- ==> [M•]+(g) + 2e-
and fragmentation equations assume [M]+ is the start of the
processes and all species are in a gaseous state.
I've not usually shown an unpaired electron on e.g. an ion or a non-ionised
alkyl radical R e.g.
[M•]+ ==> [X]+ + R•,
but you should be aware this is a more accurate depiction of some
processes.
I've used simplified equations to show how some of
the ions that might be formed in the fragmentation pattern for the
mass spectrum of 1,4-dioxane and only the formation of singly charged
positive are considered for the mass spectrum of 1,4-dioxane .
I've included a stick diagram and table of m/z ions for the mass spectrum of
1,4-dioxane
and doing the mass spectrum analysis under standard conditions,
databases can be compiled based on complex fingerprint patterns, often involving
the relative intensities of many fragment ions, and used to identify compounds including
1,4-dioxane.
In selected cases, where two
different fragment ions have the same integer m/z value,
I've pointed out that modern mass spectrometers can measure
relative ion mass to four decimal places. So, using
accurate isotopic masses, I've calculated and compared the accurate ion
masses if appropriate for 1,4-dioxane. BUT strictly speaking, 0.0005 should be deducted
for singly charged ions to account for the loss of the
electron in their formation. I have NOT done this for
1,4-dioxane,
but the mass spectrometer software does!
 Interpreting the fragmentation pattern of the mass spectrum of 1,4-dioxane
[M]+ is the molecular ion peak (M) with an m/z of
88 corresponding to [C4H8O2]+,
the original 1,4-dioxane molecule minus an electron.
The small M+1 peak at m/z 89, corresponds to an ionised
1,4-dioxane
molecule with one 13C atom in it i.e. an ionised 1,4-dioxane molecule of
formula [13C12C3H8O2]+
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.
1,4-dioxane has 4 carbon atoms, so on
average, ~1 in 5 molecules will contain a 13C atom.
The most abundant ion of the molecule under mass
spectrometry investigation (1,4-dioxane) is usually given an arbitrary abundance value of
100, called the base ion peak, and all other abundances
('intensities') are measured against it.
The base ion peak for
the mass spectrum of 1,4-dioxane is the m/z 28 ion
[C2H4]+
Identifying the species giving the most prominent peaks
(apart from M) in the fragmentation pattern of 1,4-dioxane.
Unless otherwise indicated, assume the carbon atoms in
1,4-dioxane are the 12C isotope.
The parent molecular ion for
the mass spectrum of 1,4-dioxane is the m/z 88 ion
[C4H8O2]+
Some of the possible positive ions, [molecular fragment]+,
formed in the mass spectrometry of 1,4-dioxane.
|
m/z value of
[fragment]+ |
87 |
59 with 13C |
58 |
57 |
45 |
44 |
43 |
42 |
|
[molecular fragment]+ |
[C4H7O2]+ |
[C3H6O]+ |
[C3H6O]+ |
[C3H5O]+ |
[C2H5O]+ |
[C2H4O]+ |
[C2H3O]+ |
[C2H2O]+ |
|
m/z value of
[fragment]+ |
31 ? |
30 |
29 or [CHO]+? |
28 |
28 |
27 |
26 |
15 ? |
|
[molecular fragment]+ |
[CH3O]+ |
[CH2O]+ |
[13C12CH4]+ |
[C2H4]+ |
[CO]+ |
[C2H3]+ |
[C2H2]+ |
[CH3]+ |
Analysing and explaining the principal ions in the
fragmentation pattern of the mass spectrum of 1,4-dioxane
PLEASE NOTE
I have found it difficult to find 'authentic' equations to explain mass
spectra fragmentation patterns and it is complex chemistry! I've identified
the formulae of the ionised fragments on the mass spectrum diagram, but the
equations are from the internet or my conjecture as to how the ions might be
formed - please take care in using the information, especially for
assignments at university or pre-university level.
Atomic masses: H = 1; C = 12; O = 16
Bond enthalpies kJ/mol: C-C = 348; C-H = 412;
C-O = 360
Possible
equations to explain the most abundant ion peaks of 1,4-dioxane
(tabulated above)
There are lots of
possibilities, and you can get double C-C or C-O bond scissions in the
parent molecular ion!
Formation of m/z 87 ion:
[C4H8O2]+ ===> [C4H7O2]+
+ H
C-H bond scission, loss of hydrogen atom,
mass
change 88 - 1 = 87 (M-1 ion peak)
Formation of m/z 58 ion:
[C4H8O2]+ ===> [CH2CH2OCH2]+
+ CH2O
C-C and C-O bond scission of the ring
of the parent molecular ion, followed by loss of
CH2O.
mass change 88 - 30 = 58
(M-30 ion peak)
The m/z ion 59
will be formed in the same process, but the fragment ion has one
carbon-13 isotope in it i.e.
[13C12C2H6O]+
because from the molecular structure of 1,4-dioxane, the
[C3H7O]+
ion is less likely to be formed?
Note that an accurate mass
spectrometer can sort them out, it can measure relative fragment ion
masses to four decimal places e.g. using v ery accurate relative isotopic masses,
12C
= 12.0000 13C = 13.0034, 1H = 1.0078, 16O
= 15.9949, you can then calculate
(predict) that the accurate relative ion masses are:
For m/z 59 [C3H7O]+
= 59.0495 and [13C12C2H6O]+
= 59.0451, a difference of 0.0044 in relative ion mass.
Formation of m/z 44 ion:
[CH2CH2OCH2]+ ===> [CH2CH2O]+
or [CH2OCH2]+ +
CH2
C-O or C-C bond scission of the m/z 58 ion,
mass
change 58 - 14 = 44
Formation of m/z 30 ion:
[CH2CH2O]+
or [CH2OCH2]+ ===> [CH2O]+
+ CH2
C-O or C-C bond scission in a fragment ion e.g. from
the m/z 44 ion,
mass change 44 - 14 = 30
Formation of m/z 28 ion:
[CH2CH2OCH2]+ ===> [C2H4]+
+ CH2O
C-O bond scission of the m/z 58 ion, mass change 58
- 30 = 28,
The m/z 28 ion is the base peak ion, the most
abundant and 'stable' ion fragment.
The m/z 29 ion is
likely to be formed by a similar process, but one of the carbon
atoms is a carnon-13 isotope i.e.
[13C12CH4]+
or the
[CHO]+
ion (unlikely to be the
[C2H5]+
ion), and to differentiate from other ions you can use an accurate mass
spectrometer sorts this out, measuring relative fragment ion
masses to four decimal places e.g. using very accurate relative isotopic masses,
12C
= 12.0000 13C = 13.0034, 1H = 1.0078, 16O
= 15.9949, you can then calculate
(predict) that the accurate relative ion masses are:
For m/z 29: [CHO]+ =
29.0027, [C2H5]+ = 29.0390 and
[13C12CH4]+ = 29.0346.
Similarly you can differentiate for m/z 28
ions:
[CO]+
= 27.9949 and [C2H4]+ = 28.0312,
difference of 0.0363 in relative ion mass.
Key words & phrases:
C4H8O2 image diagram on how to interpret and explain the mass spectrum of
1,4-dioxane m/z m/e base peaks, image and diagram of the mass spectrum of
1,4-dioxane, details of the mass spectroscopy of 1,4-dioxane, low and high resolution mass
spectrum of 1,4-dioxane, prominent m/z peaks in the mass spectrum of 1,4-dioxane, comparative
mass spectra of 1,4-dioxane, the molecular ion peak in the mass spectrum of
1,4-dioxane,
analysing and understanding the fragmentation pattern of the mass spectrum
of 1,4-dioxane, characteristic pattern of peaks in the mass spectrum of
1,4-dioxane, relative
abundance of mass ion peaks in the mass spectrum of 1,4-dioxane, revising the mass
spectrum of 1,4-dioxane, revision of mass spectroscopy of 1,4-dioxane, most abundant ions in the
mass spectrum of 1,4-dioxane, how to construct the mass spectrum diagram for abundance
of fragmentation ions in the mass spectrum of 1,4-dioxane, how to analyse the mass
spectrum of 1,4-dioxane, how to describe explain the formation of fragmented ions in the
mass spectra of 1,4-dioxane equations for explaining the formation of the positive ions
in the fragmentation of the ionised molecule of 1,4-dioxane recognising the base ion
peak of 1,4-dioxane interpreting interpretation the mass spectrum of 1,4-dioxane
para-dioxane p-dioxane ether
functional group How do you interpret the mass spectrum of
1,4-dioxane How to interpret
the mass spectrum of 1,4-dioxane Explanatory diagram of the mass spectrum of the
1,4-dioxane molecule in
terms of its molecular structure.
Table listing data of the m/z ion prominent main peaks in the mass spectrum of
1,4-dioxane . How to explain the mass spectrum of 1,4-dioxane . The m/z value of the
molecular ion peak in the mass spectrum of 1,4-dioxane . Identifying
1,4-dioxane from
its mass spectrum pattern. The m/z m/e peak analysis interpretation
diagram of the mass
spectrum of the 1,4-dioxane molecule. The uses of the mass spectrum of the
1,4-dioxane molecule. The distinctive features of the mass spectrum of
the 1,4-dioxane molecule explained. explaining the fragmentation pattern of the mass spectrum of
1,4-dioxane equations showing the
formation of the ionised fragments in the mass spectrum of
1,4-dioxane
what does the mass spectrum tell you about the structure and
properties of the 1,4-dioxane molecule? Data table of ionised fragments in
the mass spectrum of 1,4-dioxane and equations for their formation in the
fragmentation of the ionised 1,4-dioxane molecule.
Links associated
with
1,4-dioxane
The infrared spectrum of 1,2-dioxane (a
cyclic peroxide), not available?
The infrared spectrum of 1,3-dioxane (a cyclic ether)
The infrared spectrum of 1,4-dioxane (a cyclic ether)
The mass spectrum of 1,2-dioxane (a
cyclic peroxide), not available?
The mass spectrum of 1,3-dioxane (a cyclic ether)
The mass spectrum of 1,4-dioxane (a cyclic ether)
The H-1
spectrum of 1,2-dioxane (a cyclic peroxide)
The H-1
spectrum of 1,3-dioxane (a cyclic ether)
The H-1
spectrum of 1,4-dioxane (a cyclic ether)
The C-13
spectrum of 1,2-dioxane (a cyclic peroxide)
The C-13
spectrum of 1,3-dioxane (a cyclic ether)
The C-13
spectrum of 1,4-dioxane (a cyclic ether)
Mass spectrometry index
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