C3H8O CH3OCH2CH3 mass spectrum of methoxyethane fragmentation pattern of m/z m/e ions for analysis and identification of ethyl methyl ether image diagram doc brown's advanced organic chemistry revision notes

Advanced Organic Chemistry: Mass spectrum of methoxyethane CH₃CH₂OCH₃

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Interpreting and explaining the mass spectrum of methoxyethane

[Author © 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 spectroscopy analysis of methoxyethane [spectra page updated Mar 24th 2026 *]

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Links associated with methoxyethane

Introductory note on the mass spectrum of methoxyethane

Students and teachers please note my explanation of the mass spectrum of methoxyethane is designed for advanced, but pre-university, chemistry courses.

If M represents the methoxyethane molecule, the initial ionisation to give the molecular ion is:

M_(g) + high KE e^- ==> [M•]⁺_(g) + 2e^- and for 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 methoxyethane and only the formation of singly charged positive are considered for the mass spectrum of methoxyethane.

I've included a stick diagram and table of m/z ions for the mass spectrum of methoxyethane 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 methoxyethane.

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 the accurate ion masses, 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 methoxyethane, but the mass spectrometer software does!

C3H8O CH3OCH2CH3 mass spectrum of methoxyethane fragmentation pattern of m/z m/e ions for analysis and identification of ethyl methyl ether image diagram doc brown's advanced organic chemistry revision notes

Methoxyethane

The molecular structure and naming of aliphatic alcohols and ethers

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.

The base ion peak for the mass spectrum of methoxyethane is m/z 45 ion [C₂H₅O]⁺

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 or fragments are the ¹²C isotope.

Some of the possible positive ions, [molecular fragment]⁺, formed in the mass spectrometry of methoxyethane.

The parent molecular ion is the m/z 60 ion [C₃H₈O]⁺ or [CH₃OCH₂CH₃]⁺

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

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

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 from the parent molecular ion of methoxyethane.

mass change 60 - 1 = 59 (M-1 ion peak)

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 (M-15 ion peak)

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 molecule 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 (M-29 ion peak)

Formation of m/z 29 ion:

[CH₃OCH₂CH₃]⁺ ===> [CH₂CH₃]⁺ + CH₃O

C-O bond scission of the parent molecular ion,

mass change: 60 - 31 = 29 (M-31 ion peak)

The alternative ionisation to the formation of the m/z 31 ion from the parent molecular ion of methoxyethane (above).

The m/z ions 25, 26, 27 and 28 can be formed by loss of hydrogen atoms from the m/z 29 ion.

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 (M-45 ion peak)

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.

	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 ethoxyethane (in the absence of 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
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.

	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
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.

	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
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.

	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
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.

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What next? 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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