Advanced Organic Chemistry: Mass spectrum of 2-methoxypropane CH3CH(OCH3)CH3

HOME PAGE * SEARCH * GCSE Level Chemistry age ~14-16 * Advanced Level Chemistry age ~16-19

Interpreting and explaining the mass spectrum of 2-methoxypropane

[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 2-methoxypropane (mass spectra) [spectra page updated April 3rd 2026 *]

  email doc brown  Re-edit mass spectrum of (CH3)2CHOCH3

 Links associated with 2-methoxypropane

 This is a BIG chemistry website, PLEASE take time to explore it

 Mass spectrometry - spectra index  *  [privacy policy, cookies and disclaimer]

Introductory note on the mass spectrum of 2-methoxypropane

Students and teachers please note my explanation of the mass spectrum of 2-methoxypropane is designed for advanced, but pre-university, chemistry courses.

If M represents the 2-methoxypropane 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 2-methoxypropane.

I've included a stick diagram and table of m/z ions for the mass spectrum of 2-methoxypropane 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 2-methoxypropane.

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 2-methoxypropane. 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 2-methoxypropane, but the mass spectrometer software does!

mass spectrum of 2-methoxypropane C4H10O CH3CH(OCH3)CH3 fragmentation pattern of m/z m/e ions for analysis and identification of methyl isopropyl ether image diagram doc brown's advanced organic chemistry revision notes 

2-methoxypropane    C4H10    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

The molecular structure and naming of aliphatic alcohols and isomeric ethers

Interpreting the fragmentation pattern of the mass spectrum of 2-methoxypropane

[M]+ is the molecular ion peak (M) with an m/z of 74 corresponding to [C4H10O]+, the original 2-methoxypropane molecule minus an electron, [CH3OCH(CH3)2]+

The small M+1 peak at m/z 75, corresponds to an ionised 2-methoxypropane molecule with one 13C atom in it i.e. an ionised 1-methoxypropane molecule of formula [13C12C3H10O]+

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.

2-methoxypropane has 4 carbon atoms, so on average, ~1 in 25 molecules will contain a 13C atom.

You can also get an m/z 75 (M+1) ion from a collision between a hydrogen radical and the molecular ion.

[M]+  +  H•  ==>  [MH]+

The most abundant ion of the molecule under mass spectrometry investigation (2-methoxypropane) 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 peak ion for the mass spectrum of 2-methoxypropane is the m/z 59 ion [C3H7O]+

Identifying the species giving the most prominent peaks (apart from M) in the fragmentation pattern of 2-methoxypropane.

Unless otherwise indicated, assume the carbon atoms in 2-methoxypropane are the 12C isotope.

Some of the possible positive ions, [molecular fragment]+, formed in the mass spectrometry of 2-methoxypropane.

The parent molecular ion of 2-methoxypropane m/z 170: [CH3OCH(CH3)2]+
m/z value of [fragment]+ 73 60 59 45 43 42
[molecular fragment]+ [C4H9O]+ [13C12C2H7O]+

or  [C3H8O]+

 [C3H7O]+ [C2H5O]+ [C3H7]+ [C3H6]+
m/z value of [fragment]+ 41 39 31 29 27 15
[molecular fragment]+ [C3H5]+ [C3H3]+ [CH3O]+ [C2H5]+ [C2H3]+ [CH3]+

Analysing and explaining the principal ions in the fragmentation pattern of the mass spectrum of 2-methoxypropane

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 (~1% 13); O = 16

Bond enthalpies kJ/mol: C-C = 348; C-H = 412;  C-O = 360

Suggested possible equations to explain the most abundant ion peaks of 2-methoxypropane (tabulated above)

Formation of m/z 73 ion:

[CH3OCH(CH3)2]+  ===>  [C4H9O]+  +  H

C-H bond fission leading to H atom loss,

mass change 74 - 1 = 73 (M-1 ion peak)

The m/z 73 ion most likely has the structure [CH2OCH(CH3)2]+.

Formation of m/z 59 ion:

[CH3OCH(CH3)2]+  ===>  [OCH(CH3)2]+  +  CH3

mass change 74 - 15 = 59 (M-15 ion peak)

C-C bond scission of the parent molecular ion, loss of methyl group.

The m/z 59 ion is the base peak ion, the most abundant and 'stable' ion fragment.

The m/z 60 ion will be formed in the same way, same structure as the m/z 59 ion, but containing a carbon-13 isotope atom i.e. [13C12C2H7O]+ and more likely than the alternative m/z 60 ion [C3H8O]+?

(Looks about the right ratio of 25 : 1 for m/z ions 59 : 60)

Note that an accurate mass spectrometer can sort them out, it can measure 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 60: [13C12C2H7O]+ = 60.02549 and [C3H8O]+ = 60.0213, difference of 0.0316 in ion relative mass, no problem!

Formation of m/z 43 ion:

[CH3OCH(CH3)2]+  ===>  [CH(CH3)2]+  +  CH3O

C-O bond scission of the parent molecular ion, loss of methoxy fragment,

mass change 74 - 31 = 43 (M-31 ion peak)

The m/z 43 ion can lose protons to give the m/z ions 42, 41 and 39.

Formation of m/z 31 ion:

[CH3OCH(CH3)2]+  ===>  [CH3O]+  +  CH(CH3)2

C-O bond scission of the parent molecular, loss of the alkyl fragment,

mass change 74 - 43 = 31 (M-43 ion peak)

Note m/z 31 and 43 ions are formed by the same C-O bond scission, but the m/z 43 ion is more stable - a secondary carbocation (+I effect of methyl groups), so shows up as a more intense peak.

Formation of m/z 29 ion:

[C3H7]+  ===>  [C2H5]+  +  CH2

Perhaps from the m/z 43 ion?

Formation of m/z 15 ion:

[CH3OCH(CH3)2]+  ===>  [CH3]+  +  OCH(CH3)2

C-O bond scission, loss of methoxy fragment,

mass change 74 - 59 = 15 (M-59 ion peak)

The methyl ion can also be formed from other fragments by C-C or C-O bond scission.

Key words & phrases: C4H10O CH3CH(OCH3)CH3 image diagram on how to interpret and explain the mass spectrum of 2-methoxypropane m/z m/e base peaks, image and diagram of the mass spectrum of 2-methoxypropane, details of the mass spectroscopy of 2-methoxypropane,  low and high resolution mass spectrum of 2-methoxypropane, prominent m/z peaks in the mass spectrum of 2-methoxypropane, comparative mass spectra of 2-methoxypropane, the molecular ion peak in the mass spectrum of 2-methoxypropane, analysing and understanding the fragmentation pattern of the mass spectrum of 2-methoxypropane, characteristic pattern of peaks in the mass spectrum of 2-methoxypropane, relative abundance of mass ion peaks in the mass spectrum of 2-methoxypropane, revising the mass spectrum of 2-methoxypropane, revision of mass spectroscopy of 2-methoxypropane, most abundant ions in the mass spectrum of 2-methoxypropane, how to construct the mass spectrum diagram for abundance of fragmentation ions in the mass spectrum of 2-methoxypropane, how to analyse the mass spectrum of 2-methoxypropane, how to describe explain the formation of fragmented ions in the mass spectra of 2-methoxypropane equations for explaining the formation of the positive ions in the fragmentation of the ionised molecule of 2-methoxypropane recognising the base ion peak of 2-methoxypropane interpreting interpretation the mass spectrum of 2-methoxypropane (CH3)2CHOCH3 methyl isopropyl ether How do you interpret the mass spectrum of 2-methoxypropane How to interpret the mass spectrum of 2-methoxypropane Explanatory diagram of the mass spectrum of the 2-methoxypropane molecule in terms of its molecular structure. Table listing data of the m/z ion prominent main peaks in the mass spectrum of 2-methoxypropane. How to explain the mass spectrum of 2-methoxypropane. The m/z value of the molecular ion peak in the mass spectrum of 2-methoxypropane. Identifying 2-methoxypropane from its mass spectrum pattern. The m/z m/e peak analysis interpretation diagram of the mass spectrum of the 2-methoxypropane molecule. The uses of the mass spectrum of the 2-methoxypropane molecule.  The distinctive features of the mass spectrum of the 2-methoxypropane molecule explained. explaining the fragmentation pattern of the mass spectrum of 2-methoxypropane equations showing the formation of the ionised fragments in the mass spectrum of 2-methoxypropane  what does the mass spectrum tell you about the structure and properties of the 2-methoxypropane molecule? Data table of ionised fragments in the mass spectrum of 2-methoxypropane and equations for their formation in the fragmentation of the ionised 2-methoxypropane molecule.

Links associated with 2-methoxypropane

The infrared spectrum of 2-methoxypropane (methyl isopropyl ether)

The H-1 NMR spectrum of 2-methoxypropane (methyl isopropyl ether)

The C-13 NMR spectrum of 2-methoxypropane (methyl isopropyl ether)

Mass spectrometry index

ALL SPECTROSCOPY INDEXES

All Advanced Organic Chemistry Notes

Use My Google search site box

Email doc b: chem55555@hotmail.com

Website content © Dr Phil Brown 2000+. All copyrights reserved on revision notes, images, quizzes, worksheets etc. Copying of Doc Brown's pre-university advanced level chemistry website material is NOT permitted. Exam revision summaries & references to science course specifications are unofficial. These organic chemistry revision notes on spectroscopy (on the mass spectrum of 2-methoxypropane) are suitable for use of pre-university students studying AQA advanced level chemistry, Edexcel advanced level chemistry, OCR advanced level chemistry, IB advanced level chemistry, WJEC (Eduqas) advanced level chemistry, CIE advanced level chemistry, CCEA advanced level chemistry, US grade 11-12 AP honors chemistry courses and they will also prove useful to 1st year undergraduate students of chemistry.

TOP OF PAGE