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Advanced Organic Chemistry: Mass spectrum of methoxyethane

Interpreting the mass spectrum of methoxyethane

Doc 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

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  alcohols and ether structure and naming (c) doc b  alcohols and ether structure and naming (c) doc b  alcohols and ether structure and naming (c) doc b  alcohols and ether structure and naming (c) doc b

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

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.

infrared spectrum of ethoxyethane wavenumbers cm-1 functional group detection fingerprint pattern identification of  diethyl ether doc brown's advanced organic chemistry revision notes 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

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.

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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