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Advanced Organic Chemistry: Carbon-13 NMR spectrum of ethene (ethylene)

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Interpreting the Carbon-13 NMR spectrum of ethene (ethylene)

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 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

13C nmr spectrum of ethene C2H4 CH2=CH2 analysis of chemical shifts ppm interpretation of C-13 chemical shifts ppm of ethylene C13 13-C nmr doc brown's advanced organic chemistry revision notes 

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 alkenes structure and naming (c) doc b  displayed formula of ethene alkenes structure and naming (c) doc b skeletal formula is only alkenes structure and naming (c) doc b

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.

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.

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.

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).

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.

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.

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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

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