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Advanced Organic Chemistry: Carbon-13 NMR spectrum of ethane

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Interpreting the Carbon-13 13C NMR spectrum of ethane

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 ethane

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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 ethane C2H6 CH3CH3 analysis of chemical shifts ppm interpretation of C-13 chemical shifts ppm of ethane 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 - ethane here.

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Interpreting the C-13 NMR spectrum of ethane

As you can see from the diagram is only one chemical shift line in the C-13 NMR spectrum of ethane indicating both carbon atoms of ethane are in the same chemical environment.

CH3CH3

13C chemical shifts (a) 8.5 ppm on the C-13 NMR spectrum diagram for ethane.

The carbon-13 NMR spectra provides direct evidence of just one carbon atom environments for the 2 carbon atoms in the ethane molecule, deduced from the presence of only one 13C NMR chemical shifts (ppm).

The appearance of just one peak in the C-13 NMR spectrum of ethane, tells you unambiguously, that both carbon atoms are equivalent to each other - in the same chemical environment.

Note that the even simpler molecule of methane CH4, will also only give one peak on a C-13 NMR spectrum.

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. The 13C chemical shift for ethane is much lower.

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Links associated with ethane

The chemistry of ALKANES revision notes INDEX

The infrared spectrum of ethane

The mass spectrum of ethane

The H-1 NMR spectrum of ethane

C-13 NMR spectroscopy index

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