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 methyl ethanoate

Interpreting the mass spectrum of methyl ethanoate (methyl acetate)

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 methyl ethanoate

mass spectrum of methyl ethanoate C3H6O2 CH3COOCH3 fragmentation pattern of m/z m/e ions for analysis and identification of methyl acetate image diagram doc brown's advanced organic chemistry revision notes 

methyl ethanoate (methyl acetate), (c) doc b,(c) doc b , (c) doc b, (c) doc b

Interpreting the fragmentation pattern of the mass spectrum of methyl ethanoate

[M]+ is the molecular ion peak (M) with an m/z of 74 corresponding to [C3H6O2]+, the original methyl ethanoate molecule minus an electron, [CH3COOCH3]+.

The small M+1 peak at m/z 75, corresponds to an ionised methyl ethanoate molecule with one 13C atom in it i.e. an ionised methyl ethanoate molecule of formula [13C12C2H6O2]+

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.

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

The most abundant ion of the molecule under mass spectrometry investigation (methyl ethanoate) 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 methyl ethanoate.

Unless otherwise indicated, assume the carbon atoms in methyl ethanoate are the 12C isotope.

Some of the possible positive ions, [molecular fragment]+, formed in the mass spectrometry of methyl ethanoate.

m/z value of [fragment]+ 59 43 42 29 ? 28 15
[molecular fragment]+ [CH3CO2]+ [CH3CO]+ [CH2CO]+ [CHO]+ [CO]+ [CH3]+

Analysing and explaining the principal ions in the fragmentation pattern of the mass spectrum of methyl ethanoate

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 methyl ethanoate (tabulated above)

Formation of m/z 59 ion:

[CH3COOCH3]+  ===>  [CH3CO2]+  +  CH3

Scission of C-O bond, loss of methyl group, mass change 74 - 15 = 59.

Formation of m/z 43 ion:

[CH3COOCH3]+  ===>  [CH3CO]+  +  CH3O

C-O bond scission, mass change 74 - 31 = 43.

The m/z 42 ion is the base peak ion, the most abundant and 'stable' ion fragment.

Proton loss gives the m/z 42 ion.

Formation of m/z 29 ion:

[?]+  ===>  [?]+  +  ?

Formation of m/z 28 ion:

[CH3CO]+  ===>  [CO]+  +  CH3

C-C bond scission of the m/z 43 ion.

Formation of m/z 15 ion:

[CH3COOCH3]+  ===>  [CH3]+  +  COOCH3

[CH3COOCH3]+  ===>  [CH3]+  +  CH3COO

[CH3CO]+  ===>  [CH3]+  +  CO

C-C or C-O bond scission in the parent molecular ion, or for larger fragment ions (e.g. m/z 43 ion).


Key words & phrases: C3H6O2 CH3COOCH3 image diagram on how to interpret and explain the mass spectrum of methyl ethanoate m/z m/e base peaks, image and diagram of the mass spectrum of methyl ethanoate, details of the mass spectroscopy of methyl ethanoate,  low and high resolution mass spectrum of methyl ethanoate, prominent m/z peaks in the mass spectrum of methyl ethanoate, comparative mass spectra of methyl ethanoate, the molecular ion peak in the mass spectrum of methyl ethanoate, analysing and understanding the fragmentation pattern of the mass spectrum of methyl ethanoate, characteristic pattern of peaks in the mass spectrum of methyl ethanoate, relative abundance of mass ion peaks in the mass spectrum of methyl ethanoate, revising the mass spectrum of methyl ethanoate, revision of mass spectroscopy of methyl ethanoate, most abundant ions in the mass spectrum of methyl ethanoate, how to construct the mass spectrum diagram for abundance of fragmentation ions in the mass spectrum of methyl ethanoate, how to analyse the mass spectrum of methyl ethanoate, how to describe explain the formation of fragmented ions in the mass spectra of methyl ethanoate equations for explaining the formation of the positive ions in the fragmentation of the ionised molecule of methyl ethanoate recognising the base ion peak of methyl ethanoate interpreting interpretation the mass spectrum of methyl ethanoate methyl acetate ester


Links associated with methyl ethanoate

The chemistry of CARBOXYLIC ACIDS and DERIVATIVES revision notes INDEX

Mass spectroscopy index

ALL SPECTROSCOPY INDEXES

All Advanced Organic Chemistry Notes

Use My Google search site box

Email doc b: chem55555@hotmail.com

TOP OF PAGE

 Doc Brown's Chemistry 

*

TOP OF PAGE