[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 propylamine (propanamine) [spectra updated Mar 28th 2026 *]

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 Mass spectrometry - spectra index

Introductory note on the mass spectrum of propylamine

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

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

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

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 propylamine, but the mass spectrometer software does!

Interpreting the fragmentation pattern of the mass spectrum of propylamine

[M]⁺ is the molecular ion peak (M) with an m/z of 59 corresponding to [C₃H₉N]⁺, the original propylamine molecule minus an electron, [CH₃CH₂CH₂NH₂]⁺

The tiny M+1 peak at m/z 60, corresponds to an ionised propylamine molecule with one ¹³C atom in it i.e. an ionised propylamine molecule of formula ¹³C¹²C₂H₉N

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.

Propylamine has 3 carbon atoms, so on average, ~1 in 33 molecules will contain a ¹³C atom.

The most abundant ion of the molecule under mass spectrometry investigation (propylamine) 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 propylamine is the m/z 30 ion [CH₂NH₂]⁺

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

The parent molecular ion for propylamine is the m/z 59 ion [C₃H₉N]⁺  or  [CH₃CH₂CH₂NH₂]⁺

Analysing and explaining the principal ions in the fragmentation pattern of the mass spectrum of propylamine (finger print pattern of ions and their abundances)

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);  N = 14

Bond enthalpies kJ/mol: C-C = 348;  C-H = 412;  C-N = 305;  N-H = 391

Possible suggested equations to explain the most abundant ion peaks of the propylamine mass spectrum

There are many fragments and lots of possible fragmentation process, some are more favoured than others, but this becomes university level analysis!

Equations to explain the most abundant ion peaks

Formation of m/z 58 ion

[C₃H₉N]⁺  ===>  [C₃H₈N]⁺  +  H

N-H bond scission in parent molecular ion, loss of proton.

mass change 59 - 1 = 58 (M-1 = 59)

Formation of m/z 41 ion (M-18 ion peak)

(i) [?]⁺  ===>  [C₃H₅]⁺  +  ?

or

(ii) [?]⁺  ===>  [C₂H₃N]⁺  +  ?

Not sure what the m/z 41 ion is most likely to be, probably (ii).

I'm not sure which fragment species predominates for this pair of ions, which might be formed by other fragmentation reactions, BUT an accurate mass spectrometer can sort them out - can measure relative fragment ion masses to four decimal places e.g.

using accurate relative isotopic masses: ¹H = 1.0078  ¹²C = 12.0000   ¹⁴N = 14.0031

Accurate relative ion masses: [C₃H₅]⁺ = 41.0390  and [C₂H₃N]⁺ = 41.0265, a difference of 0.0125 in ion relative mass can be easily resolved.

Formation of m/z 30 ion

[CH₃CH₂CH₂NH₂]⁺  ===>  [CH₂NH₂]⁺  +  CH₂CH₃

C-C bond fission in the parent molecular ion, loss of ethyl group.

Mass change 59 - 29 = 30 (M-29 ion peak)

The m/z 30 ion is the base peak, the most abundant 'stable' ion fragment.

The m/z 31 ion could be the related structure [¹³CH₂NH₂]⁺ 

Formation of m/z 29 ion

[CH₃CH₂CH₂NH₂]⁺  ===>  [CH₂CH₃]⁺  +  CH₂NH₂

C-C bond fission in the parent molecular ion, loss of ethyl group, low probability, this fragmentation is more likely to give the m/z 30 ion (above)

Mass change 59 - 30 = 29 (M-29 ion peak)

This m/z 29 ion can lose protons to generate the m/z 28, 27 and 26 ions.

The m/z 28 ion can be formed by elimination of ethene from a larger fragment of >= 2 carbon atoms and, similarly, the m/z 26 ion by the elimination of ethyne.

Formation of m/z 28 ion

[?]⁺  ===>  [C₂H₄]⁺  +  ?

Elimination of ethene from a larger fragment?

Formation of m/z 15 ion

[CH₃CH₂CH₂NH₂]⁺  ===>  [CH₃]⁺  +  CH₂CH₂NH₂

C-C bond scission to cleave away a methyl group from the parent molecular ion.

59 - 44 = 15

The infrared spectrum of propylamine (propan-1-amine, 1-aminopropane)

The H-1 NMR spectrum of propylamine (propan-1-amine, 1-aminopropane)

The C-13 NMR spectrum of propylamine (propan-1amine, 1-aminopropane)

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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 propylamine, propanamine, propan-1-amine, 1-propylamine, 1-propanamine) 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.