Advanced Organic Chemistry: Mass spectrum of butan-2-ol  (2-butanol)

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

Interpreting the mass spectrum of butan-2-ol

CH3CH(OH)CH2CH3 (2-butanol, sec-butyl alcohol)

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 butan-2-ol

Use your mobile phone in 'landscape' mode?

Links associated with butan-2-ol

Mass spectroscopy - spectra index

C4H10O CH3CH(OH)CH2CH3 mass spectrum of butan-2-ol fragmentation pattern of m/z m/e ions for analysis and identification of 2-butanol sec-butyl alcohol image diagram doc brown's advanced organic chemistry revision notes 

Butan-2-ol    C4H10O    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 

Interpreting the fragmentation pattern of the mass spectrum of butan-2-ol

[M]+ is the molecular ion peak (M) with an m/z of 74 corresponding to [C4H10O]+, the original butan-2-ol molecule minus an electron, [CH3CH(OH)CH2CH3]+.

This is a tiny peak, indicating the molecular ion is very unstable.

You might see an even smaller M+1 peak at m/z 75, corresponding to an ionised butan-2-ol molecule with one 13C atom in it i.e. an ionised butan-2-ol 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.

Butan-2-ol 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 (butan-2-ol) 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 butan-2-ol.

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

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

m/z value of [fragment]+ 73 59 57 56 55 ? 55? 45 44 ? 44 ?
[molecular fragment]+ [C4H9O]+ [C3H7O]+ [C3H5O]+ [C4H8]+ [C2H5O]+ [C4H7]+ [CH3CHOH]+ [C3H8]+ [C2H4O]+
m/z value of [fragment]+ 43 ? 43 ? 42 41 39 31 ? 29 28 27 15
[molecular fragment]+ [C3H7]+ [C2H3O]+ [C3H6]+ [C2H4O]+ [C3H3]+ [CH3O]+ [CH3CH2]+ [C2H4]+ [C2H3]+ [CH3]+

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

Atomic masses: H = 1; C = 12;  O = 16

Bond enthalpies kJ/mol: C-C = 348;  C-H = 412;  C-O = 360;  O-H = 463

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

Formation of m/z 73 ion:

[CH3CH(OH)CH2CH3]+  ===>  [C4H9O]+  +  H

C-H bond scission an loss of proton, mass change 74 - 1 = 73.

Formation of m/z 59 ion:

[CH3CH(OH)CH2CH3]+  ===>  [C3H7O]+  +  CH3

C-C bond scission an loss of methyl group from either end (?) of the parent molecular ion.

Formation of m/z 57 ion:

[?]+  ===>  [C3H5O]+  +  ?

Could be a [C4H9]+ ion ?

Formation of m/z 56 ion:

[CH3CH(OH)CH2CH3]+  ===>  [C4H8]+  +  H2O

Elimination of water from the parent molecular ion to give a positively ionised molecule of a butene.

Formation of m/z 55 ion:

[C4H9O]+  ===>  [C4H7]+  +  H2O

Elimination of water from the m/z 73 ion. Mass change 73 - 18 = 55

OR C-C bond scission of the parent molecular ion, mass change 74 - 29 = 55.

[CH3CH(OH)CH2CH3]+  ===>  [CH3CH(OH)]+  +  CH2CH3

Formation of m/z 45 ion:

[CH3CH(OH)CH2CH3]+  ===>  [CH3CHOH]+  +  CH2CH3

C-C bond scission of the parent molecular ion, mass change 74 - 29 = 45.

The m/z 45 ion is the base peak ion, the most abundant and 'stable' ion fragment.

Formation of m/z 29 ion:

[CH3CH(OH)CH2CH3]+  ===>  [CH2CH3]+  +  CH3CHOH

C-C bond scission of the parent molecular ion, mass change 74 - 45 = 29.

Formation of m/z 15 ion:

[CH3CH(OH)CH2CH3]+  ===>  [CH3]+  +  C3H7O

C-C bond scission to break off a methyl group (from either end of molecule?).

Mass change 74 - 59 = 15 (see also formation of m/z 59, either fragment may be ionised.


Key words & phrases: C4H10O CH3CH(OH)CH2CH3 image diagram on how to interpret and explain the mass spectrum of butan-2-ol m/z m/e base peaks, image and diagram of the mass spectrum of butan-2-ol, details of the mass spectroscopy of butan-2-ol,  low and high resolution mass spectrum of butan-2-ol, prominent m/z peaks in the mass spectrum of butan-2-ol, comparative mass spectra of butan-2-ol, the molecular ion peak in the mass spectrum of butan-2-ol, analysing and understanding the fragmentation pattern of the mass spectrum of butan-2-ol, characteristic pattern of peaks in the mass spectrum of butan-2-ol, relative abundance of mass ion peaks in the mass spectrum of butan-2-ol, revising the mass spectrum of butan-2-ol, revision of mass spectroscopy of butan-2-ol, most abundant ions in the mass spectrum of butan-2-ol, how to construct the mass spectrum diagram for abundance of fragmentation ions in the mass spectrum of butan-2-ol, how to analyse the mass spectrum of butan-2-ol, how to describe explain the formation of fragmented ions in the mass spectra of butan-2-ol equations for explaining the formation of the positive ions in the fragmentation of the ionised molecule of butan-2-ol recognising the base ion peak of butan-2-ol interpreting interpretation the mass spectrum of butan-2-ol  in sec-butyl alcohol CH3CH2CH(OH)CH3 2-butanol How do you interpret the mass spectrum of 2-butanol butan-2-ol How to interpret the mass spectrum of 2-butanol butan-2-ol Explanatory diagram of the mass spectrum of the 2-butanol butan-2-ol molecule in terms of its molecular structure. Listing data of the prominent main peaks in the mass spectrum of 2-butanol butan-2-ol. How to explain the mass spectrum of 2-butanol butan-2-ol. The m/z value of the molecular ion peak in the mass spectrum of 2-butanol butan-2-ol. Identifying 2-butanol butan-2-ol from its mass spectrum pattern. The m/z m/e peak analysis of the mass spectrum of the 2-butanol butan-2-ol molecule. The uses of the mass spectrum of the 2-butanol butan-2-ol molecule. The distinctive features of the mass spectrum of the 2-butanol butan-2-ol molecule explained. explaining the fragmentation pattern of the mass spectrum of 2-butanol butan-2-ol equations showing the formation of the ionised fragments in the mass spectrum of 2-butanol butan-2-ol what does the mass spectrum tell you about the structure and properties of the 2-butanol butan-2-ol molecule?


Links associated with butan-2-ol

The infrared spectrum of butan-2-ol (sec-butyl alcohol)

The H-1 NMR spectrum of butan-2-ol (sec-butyl alcohol)

The C-13 NMR spectrum of butan-2-ol (sec-butyl alcohol)

The chemistry of ALCOHOLS 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 and indexes