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 1,1,2-trichloroethane

Interpreting the mass spectrum of 1,1,2-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 1,1,2-trichloroethane

mass spectrum of 1,1,2-trichloroethane C2H3Cl3 Cl2CHCH2Cl fragmentation pattern of m/z m/e ions for analysis and identification of 1,1,2-trichloroethane image diagram doc brown's advanced organic chemistry revision notes 

1,1,2-trichloroethane  Cl2CH-CH2Cl  or  CHCl2CH2Cl

Interpreting the fragmentation pattern of the mass spectrum of 1,1,2-trichloroethane

[M]+ is the molecular ion peak (M) with an m/z of 132, 134 or 136 (and theoretically 138) corresponding to [C2H3Cl3]+, the original 1,1,2-trichloroethane molecule minus an electron, [Cl2CHCH2Cl]+, depending on the chlorine isotopic composition of the 1,1,2-trichloroethane molecule.

Since chlorine consists of two isotopes, 35Cl and 37Cl (in a 3:1 ratio), there are four possibilities for the 'isotopic' molecular formula of 1,1,2-trichloroethane molecule, therefore theoretically four possible molecular ions.

(i) M = 132 for C2H335Cl3,  (ii) M = 134 for C2H335Cl237Cl,  (iii) M = 136 for C2H335Cl37Cl2

and  (iv) M = 138 for C2H337Cl3., the increments of two are due the mass difference between 35Cl and 37Cl.

Because 35Cl is more abundant, ions of (i) and (ii) are the most likely to be observed.

There is a smaller chance of the m/z ion 136 and a very low probability of the m/z 138 ion.

This is what you observe in the spectrum, the abundances being (i) ~ (ii) > (iii) >> (iv).

The most abundant ion of the molecule under mass spectrometry investigation (1,1,2-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 1,1,2-trichloroethane.

Unless otherwise indicated, assume the carbon atoms in 1,1,2-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 1,1,2-trichloroethane.

m/z value of [fragment]+ 101 99 98 97 96 95
[molecular fragment]+ [C2H337Cl2]+ [C2H335Cl37Cl]+ [C2H235Cl37Cl]+ [C2H335Cl2]+ [C2H235Cl2]+ [C2H335Cl2]+
m/z value of [fragment]+ 87 85 83 64 ? 63 62 ? 61 60
[molecular fragment]+ [CH37Cl2]+ [CH35Cl37Cl]+ [CH35Cl2]+ [C2H337Cl]+ [C2H237Cl]+ [C2H335Cl]+ [C2H235Cl]+ [C2H35Cl]+
m/z value of [fragment]+ 51 49 36 35 27 26 25
[molecular fragment]+ [CH237Cl]+ [CH235Cl]+ [H35Cl]+ [35Cl]+ [C2H3]+ [C2H2]+ [C2H]+

Analysing and explaining the principal ions in the fragmentation pattern of the mass spectrum of 1,1,2-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 1,1,2-trichloroethane (tabulated above)

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

[Cl2CHCH2Cl]+  ===>  [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.

[Cl2CHCH2Cl]+  ===>  [Cl]+  +  C2H3Cl2

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

Formation of m/z 96, 98 and 100 ions:

[Cl2CHCH2Cl]+  ===>  [C2H2Cl2]+  +  HCl

Elimination of hydrogen chloride from the parent molecular ion.

Possible structures of ion [CHCl=CHCl]+ or [Cl2C=CH2]+.

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 83, 85 and 87 ions:

[Cl2CHCH2Cl]+  ===>  [CHCl2]+  +  CH2Cl

C-C bond scission of the parent molecular ion of 1,1,2-trichloroethane.

Formation of m/z 62 and 64 ions ?:

[Cl2CHCH2Cl]+  ===>  [C2H3Cl]+  +  Cl2

Elimination of chlorine molecule from the parent molecular ion ?

Structure of ion ? [CH2=CHCl]+

However, more likely to be formed by the loss of a Cl radical from the m/z 97, 99 and 101 ions ...

[C2H3Cl2]+  ===>  [C2H3Cl]+  +  Cl

... essentially a 2 stage process from the parent molecular ion.

Formation of m/z 61 and 63 ions:

[C2H3Cl2]+  ===>  [C2H2Cl]+  +  HCl

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

Formation of m/z 49 and 51 ions:

[Cl2CHCH2Cl]+  ===>  [CH2Cl]+  +  CHCl2

C-C bond scission.

You can see these ions are roughly in a 3:1 ratio.

Note this alternative ionisation compared to the formation of the m/z 83, 85 and 87 ions.

Formation of m/z ? ion:

[?]+  ===>  [?]+  +  ?


Key words & phrases: C2H3Cl3 Cl2CHCH2Cl CHCl2CH2Cl ClCH2CHCl2 CH2ClCHCl2 image diagram on how to interpret and explain the mass spectrum of 1,1,2-trichloroethane m/z m/e base peaks, image and diagram of the mass spectrum of 1,1,2-trichloroethane, details of the mass spectroscopy of 1,1,2-trichloroethane,  low and high resolution mass spectrum of 1,1,2-trichloroethane, prominent m/z peaks in the mass spectrum of 1,1,2-trichloroethane, comparative mass spectra of 1,1,2-trichloroethane, the molecular ion peak in the mass spectrum of 1,1,2-trichloroethane, analysing and understanding the fragmentation pattern of the mass spectrum of 1,1,2-trichloroethane, characteristic pattern of peaks in the mass spectrum of 1,1,2-trichloroethane, relative abundance of mass ion peaks in the mass spectrum of 1,1,2-trichloroethane, revising the mass spectrum of 1,1,2-trichloroethane, revision of mass spectroscopy of 1,1,2-trichloroethane, most abundant ions in the mass spectrum of 1,1,2-trichloroethane, how to construct the mass spectrum diagram for abundance of fragmentation ions in the mass spectrum of 1,1,2-trichloroethane, how to analyse the mass spectrum of 1,1,2-trichloroethane, how to describe explain the formation of fragmented ions in the mass spectra of 1,1,2-trichloroethane equations for explaining the formation of the positive ions in the fragmentation of the ionised molecule of 1,1,2-trichloroethane recognising the base ion peak of 1,1,2-trichloroethane interpreting interpretation the mass spectrum of 1,1,2-trichloroethane formula old names functional group


Links associated with 1,1,2-trichloroethane

The chemistry of HALOGENOALKANES (haloalkanes) 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