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Advanced Organic Chemistry: Carbon-13 NMR spectrum of methoxymethane

The Carbon-13 NMR spectrum of methoxymethane (dimethyl ether)

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 methoxymethane

C2H6O CH3OCH3 C-13 nmr spectrum of methoxymethane analysis of chemical shifts ppm interpretation of 13C chemical shifts ppm of dimethyl ether 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 - methoxymethane here.

Methoxymethane (dimethyl ether) alcohols and ether structure and naming (c) doc b alcohols and ether structure and naming (c) doc b alcohols and ether structure and naming (c) doc b alcohols and ether structure and naming (c) doc b alcohols and ether structure and naming (c) doc b

Revision notes on the structure and naming (nomenclature) of aliphatic ALCOHOLS and ETHERS

Interpreting the C-13 NMR spectrum of methoxymethane

As you can see from the diagram above there is just one chemical shift line in the C-13 NMR spectrum of methoxymethane indicating only one chemical environment of the two carbon atoms of methoxymethane.

CH3OCH3

(Note there is just one colour indicating the one chemical environment of the 2 carbon atoms in methoxymethane - the molecule is symmetrical so both carbon atoms are equivalent to each other).

13C chemical shift (a) is 59.3 ppm for C-13 NMR spectrum diagram for methoxymethane.

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

See also comparing the IR, mass, 1H NMR and 13C NMR spectra of isomers of C2H6O below.

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Comparing the infrared, mass, 1H NMR and 13C NMR spectra of the 2 isomers of C2H6O

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 ethanol (ethyl alcohol) and methoxymethane (dimethyl ether) image sizes.

INFRARED SPECTRA: Apart from the significant differences in the fingerprint region at wavenumbers 1500 to 400 cm-1, the most striking difference is the broad O-H stretching band ~3400 cm-1, found in the infrared spectrum of alcohols, but absent in the infrared spectrum of ethers.

MASS SPECTRA: Both ethanol and methoxymethane show some similarities in their mass spectra, but their base ion peaks are quite different - for ethanol it is m/z 31 and for methoxymethane it is m/z 45.

1H NMR SPECTRA: The 1H NMR spectra of ethanol and methoxymethane are quite significantly different. Ethanol gives 3 peaks in the proton ratio 3:2:1 (3 different chemical environments), whereas methoxymethane only gives one 1H chemical shift peak (all 6 protons in the same chemical environment).

13C NMR SPECTRA: The 13C NMR spectra of ethanol and methoxymethane are different. Ethanol gives two 13C resonances, but methoxymethane only one (2 different 13C chemical environments and a 13C single chemical environment).


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