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Interpreting the
Carbon-13 NMR spectrum of ethene
(ethylene)
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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 C-13 NMR spectra of ethene
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C-13
NMR spectroscopy - spectra index
See also
comparing the infrared, mass, 1H NMR and 13C NMR spectra of ethane and
ethene
TMS is the acronym for tetramethylsilane, formula Si(CH3)4,
whose 13C atoms are arbitrarily given a chemical shift of 0.0
ppm. This is the 'standard' in 13C NMR spectroscopy and all other
13C resonances, called chemical shifts, are measured with
respect to the TMS, and depend on the
individual (electronic) chemical environment of the 13C atoms in
an organic molecule - ethene here.
Ethene
C2H4
 displayed formula of ethene
 skeletal formula is only
Interpreting the C-13 NMR spectrum of ethene
As you can see from the diagram above there is only
one chemical shift line in the C-13 NMR spectrum of
ethene
indicating the same chemical environment of the two carbon
atoms of ethene.
CH2=CH2
13C chemical shift (a)
123 ppm on the C-13 NMR
spectrum diagram for the alkene ethene.
The carbon-13 NMR spectra provides direct evidence of
only one carbon atom environments for the two carbon atoms in the
ethene molecule,
deduced from the presence of only one 13C NMR chemical
shift of 123 ppm.
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Comparing the infrared, mass, 1H NMR and 13C NMR
spectra of
ethane and ethene
NOTE: The images are linked to their
original detailed spectral analysis pages AND can be doubled in
size with touch screens to
increase the definition to the original ethane and
ethene image sizes. |
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INFRARED SPECTRA:
Apart from the significant differences in the fingerprint region at
wavenumbers 1500 to 400 cm-1, the most striking
differences are (i) the band at ~1900 cm-1 for ethene,
absent in the ethane spectrum, (ii) the bands at 800 cm-1
for ethane (CH3 vibrations), absent or much weaker in
ethene, and (iii) the strong absorptions at ~1000 cm-1
for ethene, completely absent in the ethane spectrum. |
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MASS SPECTRA: Both
ethane and ethene show some similarities in their mass
spectra e.g. m/z ions 25 to 28 for [C2Hx]+
(x = 1 to 4) ions and in both cases the base ion peak has an m/z
of 28. However, the molecular ion peaks will be different
because of their different relative molecular masses i.e. ethane
m/z 30 and ethene m/z 28. Ethane also has a prominent m/z ion
peak of 29, which is tiny in the ethene mass spectrum (and only
due to 1% 13C atoms in the parent molecular ion). |
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1H NMR SPECTRA: The 1H NMR spectra of
ethane and ethene are similar in that that both give one single
singlet resonance line in their proton NMR spectra. All the
protons in each molecule are equivalent to each other and occupy
the same chemical environment due to the symmetry of the
molecule, so no resonance splitting. However the two 1H
chemical shifts are significantly different due the different
shielding effects of the -CH3 and =CH2
groupings respectively. |
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13C NMR SPECTRA: The
1C NMR spectra of ethane and ethene are similar in that that
both give one single resonance line in their carbon-13 NMR
spectra. In both molecules the two carbon atoms occupy the same
chemical environment due to the symmetry of the molecule.
However the two 13C chemical shifts are significantly
different due the different shielding effects of the -CH3
and =CH2
groupings respectively. Ethene has a much greater 13C
NMR chemical shift. |
Key words & phrases:
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assignment of chemical shifts in the 13C
NMR spectrum of ethene type functional group alkene ethylene
Links associated
with ethene
The chemistry of ALKENES
revision notes INDEX
The infrared spectrum of ethene ('ethylene')
The mass spectrum of ethene ('ethylene')
The H-1 NMR spectrum of ethene ('ethylene')
C-13
NMR spectroscopy index
ALL SPECTROSCOPY INDEXES
All Advanced Organic
Chemistry Notes
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