image diagram mass spectrum of methylbenzene fragmentation pattern of ions for analysis and identification of methylbenzene doc brown's advanced organic chemistry revision notes

Advanced Organic Chemistry: Mass spectrum of Methylbenzene (Toluene) C₆H₅CH₃

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

Interpreting the mass spectrum of Methylbenzene (Toluene)

[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 methylbenzene [spectra page updated Mar 25th 2026 *]

email doc brown Re-edit mass spectrum of C₆H₅CH₃

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

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

Links associated with methylbenzene

Introductory note on the mass spectrum of methylbenzene

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

If M represents the methylbenzene 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 methylbenzene and only the formation of singly charged positive are considered for the mass spectrum of methylbenzene.

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

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 methylbenzene, but the mass spectrometer software does!

image diagram mass spectrum of methylbenzene fragmentation pattern of ions for analysis and identification of methylbenzene doc brown's advanced organic chemistry revision notes

Methylbenzene C₇H₈, C₆H₅CH₃ , ,

The molecular structure and naming of aromatic compounds
Interpreting the mass spectrum of Methylbenzene (Toluene)

[M]⁺ is the molecular ion peak (M) with an m/z of 92 corresponding to [C₇H₈]⁺, the original methylbenzene molecule minus an electron, [C₆H₅CH₃]⁺

The small M+1 peak at m/z 93, corresponds to an ionised methylbenzene molecule with one ¹³C atom in it i.e. an ionised methylbenzene molecule of formula ¹³C¹²C₆H₈

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.

Methylbenzene has 7 carbon atom, so on average, ~1 in 14 molecules will contain a ¹³C atom.

The most abundant ion of the molecule under mass spectrometry investigation (methylbenzene) is usually given an arbitrary value of 100, called the base ion peak, and all other abundances ('intensities') are measured against it.

In this case the base ion peak is m/z ion 91 [C₇H₇]⁺

The parent molecular ion is m/z 92 [C₇H₈]⁺ which seems to readily lose an electron to give the m/z 91 ion above.

Identifying the species giving the most prominent peaks (apart from M) in the fragmentation pattern of the mass spectrum of methylbenzene.

m/z value of [fragment]⁺	91	90	89	77	65	63	62	51	50	39
[molecular fragment]⁺	[C₇H₇]⁺	[C₇H₆]⁺	[C₇H₅]⁺	[C₆H₅]⁺	[C₅H₅]⁺	[C₅H₃]⁺	[C₅H₂]⁺	[C₄H₃]⁺	C₄H₂]⁺	[C₃H₃]⁺

Explaining the principal fragments of the mass spectrum of methylbenzene

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.

Suggested equations to explain the fragment ions observed in the mass spectrum of methylbenzene

Formation of the m/z 89, 90 and 91 and ion

(i) m/z 91 corresponds to proton loss from the ionised methylbenzene molecule (parent molecular ion)

[C₆H₅CH₃]⁺ ===> [C₆H₅CH₂]⁺ + H

[C₇H₈]⁺ ===> [C₇H₇]⁺ + H

mass change 92 - 1 = 91 (M-1 ion peak) and the base ion peak.

(ii) m/z 90 ion from loss of a hydrogen molecule from parent molecular ion

[C₇H₈]⁺ ===> [C₇H₆]⁺ + H₂

mass change 92 - 2 = 90 (M-2 ion peak)

(iii) m/z 89 ion from loss of hydrogen from the m/z 91 ion

[C₇H₇]⁺ ===> [C₇H₇]⁺ + H₂

mass change 91 - 2 = 89 (M-3 ion peak)

Formation of the m/z 77 ion

[C₇H₈]⁺ ===> [C₆H₅]⁺ + CH₃

C-C bond fission and loss of alkyl methyl group,

mass change 92 - 15 = 77

Low intensity-probability, BUT it is quite a characteristic fragment ion from mono-substituted benzene ring aromatic compounds

Formation of the m/z 65 ion

[C₇H₇]⁺ ===> [C₅H₅]⁺ + C₂H₂

Loss of ethyne molecule from the m/z 91 ion (found this on the internet)

Mass change 91 - 26 = 65

Further loss of hydrogen atoms gives the m/z 62 and 63 ions.

Formation of m/z ions <65

Further fragmentation by loss of carbon and hydrogen atoms from m/z ions >64 e.g.

loss of ethyne from the m/z 65 ion

[C₅H₅]⁺ ===> [C₃H₃]⁺ + C₂H₂

Mass change 65 - 26 = 39

You sometimes see sequences corresponding to successive loss of CH2

e.g m/z decrease 65 ==> 51 ==> 39

but there are lots of possibilities!

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

What next? links associated with methyl benzene

The infrared spectrum of methylbenzene

The C-13 NMR spectrum of methylbenzene

The H-1 NMR spectrum of methylbenzene

The chemistry of AROMATIC COMPOUNDS revision notes INDEX

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 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.