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Advanced Organic Chemistry: Mass spectrum of 1,1,1-trichloroethane

Interpreting the mass spectrum of 1,1,1-trichloroethane

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 1,1,1-trichloroethane

mass spectrum of 1,1,1-trichloroethane C2H3Cl3 CH3CCl3 fragmentation pattern of m/z m/e ions for analysis and identification of 1,1,1-trichloroethane image diagram doc brown's advanced organic chemistry revision notes 

1,1,1-trichloroethane  Cl3C-CH3  or  CH3CCl3

Interpreting the fragmentation pattern of the mass spectrum of 1,1,1-trichloroethane

There is no [M]+ the molecular ion peak (M) with an m/z of 132, 134, 136 or 138 corresponding to [C2H3Cl3]+, the original 1,1,1-trichloroethane molecule minus an electron, depending on the chlorine isotopic composition of the 1,1,1-trichloromethane molecule Cl3CCH3.

See discussion on possible molecular ion peaks on the mass spectrum page for 1,1,2-trichloroethane, where, unlike here, you clearly observe three of the for possible molecular ion peaks for a C2H3Cl3 molecular formula molecule.

The most abundant ion of the molecule under mass spectrometry investigation (1,1,1-trichloroethane) 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 1,1,1-trichloroethane.

Unless otherwise indicated, assume the carbon atoms in 1,1,1-trichloroethane are the 12C isotope, but the chlorine atoms maybe 35Cl or 37Cl and this makes the mass spectrum even more complex to interpret.

Some of the possible positive ions, [molecular fragment]+, formed in the mass spectrometry of 1,1,1-trichloroethane.

m/z value of [fragment]+ 121 119 117 101 99 97
[molecular fragment]+ [C35Cl37Cl2]+ [C35Cl237Cl]+ [C35Cl3]+ [C2H337Cl2]+ [C2H335Cl37Cl]+ [C2H335Cl2]+
m/z value of [fragment]+ 63 62 ? 61 60 ? 38 37
[molecular fragment]+ [C2H237Cl]+ [C2H37Cl]+ [C2H235Cl]+ [C2H35Cl]+ [H37Cl]+ [37Cl]+
m/z value of [fragment]+ 36 35 28 ? 27 26 25
[molecular fragment]+ [H35Cl]+ [35Cl]+ [C2H4]+ [C2H3]+ [C2H2]+ [C2H]+

Analysing and explaining the principal ions in the fragmentation pattern of the mass spectrum of 1,1,1-trichloroethane

Atomic masses: H = 1;  C = 12;  Cl = 35 or 37 (3:1)

Bond enthalpies kJ/mol: C-C = 348;  C-H = 412;  C-Cl = 338

Possible equations to explain the most abundant ion peaks of 1,1,1-trichloroethane (tabulated above)

Formation of m/z 117, 119 and 121 ions:

[Cl3CCH3]+  ===>  [CCl3]+  +  CH3

C-C bond scission with loss of methyl radical from the parent molecular ion.

Formation of m/z 97, 99 and 101 ions:

[Cl3CCH3]+  ===>  [C2H3Cl2]+  +  Cl

C-Cl bond scission (weakest bond), loss of chlorine radical from the parent molecular ion.

The m/z 97 ion is the base peak ion, the most abundant and 'stable' ion fragment.

Alternatively, but much less probable, the Cl is ionised to give the m/z 35 and 37 ions.

[Cl3CCH3]+  ===>  [Cl]+  +  C2H3Cl2

You can see roughly a 3:1 ratio for the m/z 35 and 37 ions.

Formation of m/z 61 and 63 ions:

[C2H3Cl2]+  ===>  [C2H2Cl]+  +  HCl

Elimination of hydrogen chloride from the m/z 97 and 99 ions.

Alternatively, but very much less probable, the HCl is ionised to give the m/z 36 and 38 ions.

You can see roughly a 3:1 ratio for the m/z 36 and 38 ions.

Formation of m/z ? ion:

[?]+  ===>  [?]+  +  ?


Key words & phrases: C2H3Cl3 Cl3CCH3 CCl3CH3 CH3CCl3 image diagram on how to interpret and explain the mass spectrum of 1,1,1-trichloroethane m/z m/e base peaks, image and diagram of the mass spectrum of 1,1,1-trichloroethane, details of the mass spectroscopy of 1,1,1-trichloroethane,  low and high resolution mass spectrum of 1,1,1-trichloroethane, prominent m/z peaks in the mass spectrum of 1,1,1-trichloroethane, comparative mass spectra of 1,1,1-trichloroethane, the molecular ion peak in the mass spectrum of 1,1,1-trichloroethane, analysing and understanding the fragmentation pattern of the mass spectrum of 1,1,1-trichloroethane, characteristic pattern of peaks in the mass spectrum of 1,1,1-trichloroethane, relative abundance of mass ion peaks in the mass spectrum of 1,1,1-trichloroethane, revising the mass spectrum of 1,1,1-trichloroethane, revision of mass spectroscopy of 1,1,1-trichloroethane, most abundant ions in the mass spectrum of 1,1,1-trichloroethane, how to construct the mass spectrum diagram for abundance of fragmentation ions in the mass spectrum of 1,1,1-trichloroethane, how to analyse the mass spectrum of 1,1,1-trichloroethane, how to describe explain the formation of fragmented ions in the mass spectra of 1,1,1-trichloroethane equations for explaining the formation of the positive ions in the fragmentation of the ionised molecule of 1,1,1-trichloroethane recognising the base ion peak of 1,1,1-trichloroethane interpreting interpretation the mass spectrum of 1,1,1-trichloroethane formula old names functional group


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