HOME PAGE * KS3 SCIENCES * GCSE BIOLOGY CHEMISTRY PHYSICS * ADVANCED LEVEL CHEMISTRY

SPECTROSCOPY INDEXES  *  All Advanced Organic Chemistry Notes  *  [SEARCH BOX]

Advanced Organic Chemistry: Mass spectrum of 2-methylpropanal

Scroll down and take time to study the content and/or follow links or [Use the website search box]

Interpreting the mass spectrum of 2-methylpropanal (isobutyraldehyde)

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 2-methylpropanal

email doc brown

Use your mobile phone or ipad etc. in 'landscape' mode

This is a BIG website, you need to take time to explore it

Mass spectroscopy - spectra index

mass spectrum of 2-methylpropanal C4H8O (CH3)2CHCHO fragmentation pattern of m/z m/e ions for analysis and identification of isobutyraldehyde image diagram doc brown's advanced organic chemistry revision notes 

2-methylpropanal   C4H8O   aldehydes and ketones nomenclature (c) doc b    aldehydes and ketones nomenclature (c) doc b    aldehydes and ketones nomenclature (c) doc b

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

[M]+ is the molecular ion peak (M) with an m/z of 72 corresponding to [C4H8O]+, the original 2-methylpropanal molecule minus an electron, [(CH3)2CHCHO]+.

The small M+1 peak at m/z 73, corresponds to an ionised 2-methylpropanal molecule with one 13C atom in it i.e. an ionised 2-methylpropanal molecule of formula [13C12C3H8O]+

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

The most abundant ion of the molecule under mass spectrometry investigation (2-methylpropanal) 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 2-methylpropanal.

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

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

The parent molecular ion peak, m/z 72 is for the  [(CH3)2CHCHO]+. ion.

m/z value of [fragment]+ 71 57 55 43 42 41 39 29 28 27
[molecular fragment]+ [C4H7O]+ [C3H5O]+ [C3H3O]+ [C3H7]+ [C3H6]+ [C3H5]+ [C3H3]+ [CHO]+ [C2H4]+ [C2H3]+

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

Atomic masses: H = 1; C = 12; O = 16; 

Bond enthalpies kJ/mol: C-C = 348;  C-H = 412;  C-O = 360; C=O = 743

Possible equations to explain the most abundant ion peaks of 2-methylpropanal (tabulated above)

Formation of m/z 71 ion:

[(CH3)2CHCHO]+  ===>  [C4H7O]+  +  H

Scission of C-H bond in the aldehyde group, mass change 72 - 1 = 71.

Formation of m/z 57 ion:

[(CH3)2CHCHO]+  ===>  [C3H5O]+  +  CH3

C-C bond scission in the parent molecular ion, loss of methyl group, mass change 72 - 15 = 57.

Structure of ion?: [CH3CH2CO]+  or  [CH3CHCHO]+  ?

Formation of m/z 43 ion:

[(CH3)2CHCHO]+  ===>  [(CH3)2CH]+  +  CHO

Scission of C-C bond in the parent molecular ion, mass change 72 - 29 = 43, secondary carbocation formed.

The CHO can also be ionised to give the m/z 29 ion (see below).

The m/z 43 ion is the base peak ion, the most abundant and 'stable' ion fragment.

Could the m/z 43 ion also be due to [CH3C=O]+ ?

The m/z 43 ion can lose hydrogen atoms/molecule to give the m/z ions 42 down to 37.

The m/z 44 ion could be [13C12C2H7]+ ion, in a ratio of 1:25 compared to the m/z 43 ion - see earlier note on cabon-13 abundance in the molecules of 2-methylpropanal.

Formation of m/z 29 ion:

[(CH3)2CHCHO]+  ===>  [CHO]+  +  (CH3)2CH

Scission of C-C bond in the parent molecular ion, mass change 72 - 43 = 29.


Key words & phrases: C4H8O (CH3)2CHCHO image diagram on how to interpret and explain the mass spectrum of 2-methylpropanal m/z m/e base peaks, image and diagram of the mass spectrum of 2-methylpropanal, details of the mass spectroscopy of 2-methylpropanal,  low and high resolution mass spectrum of 2-methylpropanal, prominent m/z peaks in the mass spectrum of 2-methylpropanal, comparative mass spectra of 2-methylpropanal, the molecular ion peak in the mass spectrum of 2-methylpropanal, analysing and understanding the fragmentation pattern of the mass spectrum of 2-methylpropanal, characteristic pattern of peaks in the mass spectrum of 2-methylpropanal, relative abundance of mass ion peaks in the mass spectrum of 2-methylpropanal, revising the mass spectrum of 2-methylpropanal, revision of mass spectroscopy of 2-methylpropanal, most abundant ions in the mass spectrum of 2-methylpropanal, how to construct the mass spectrum diagram for abundance of fragmentation ions in the mass spectrum of 2-methylpropanal, how to analyse the mass spectrum of 2-methylpropanal, how to describe explain the formation of fragmented ions in the mass spectra of 2-methylpropanal equations for explaining the formation of the positive ions in the fragmentation of the ionised molecule of 2-methylpropanal recognising the base ion peak of 2-methylpropanal interpreting interpretation the mass spectrum of 2-methylpropanal  methylpropanal isobutyraldehyde 2-methylpropionaldehyde iso-butyraldehyde Stick diagram of the relative abundance of ionised fragments in the fingerprint pattern of the mass spectrum of 2-methylpropanal. Table of the m/e m/z values and formula of the ionised fragments in the mass spectrum of 2-methylpropanal. The m/e m/z value of the molecular ion peak in the mass spectrum of 2-methylpropanal.  The m/e m/z value of the base ion peak in the mass spectrum of 2-methylpropanal. Possible examples of equations showing the formation of the ionised fragments in 2-methylpropanal. Revision notes on the mass spectrum of 2-methylpropanal. Matching and deducing the structure of the 2-methylpropanal molecule from its mass spectrum.


Links associated with 2-methylpropanal

The chemistry of ALDEHYDES and KETONES revision notes INDEX

The infrared spectrum of 2-methylpropanal (methylpropanal, isobutyraldehyde)

The H-1 NMR spectrum of 2-methylpropanal (methylpropanal, isobutyraldehyde)

The C-13 NMR spectrum of 2-methylpropanal (methylpropanal, isobutyraldehyde)

Mass spectroscopy index

ALL SPECTROSCOPY INDEXES

All Advanced Organic Chemistry Notes

Use My Google search site box

Email doc b: chem55555@hotmail.com

 Doc Brown's Chemistry 

*

TOP OF PAGE