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Advanced Organic Chemistry: 1H NMR spectrum of methoxymethane

H-1 hydrogen-1 (proton) 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 H-1 NMR spectra of methoxymethane

C2H6O CH3OCH3 low and high resolution 1H proton nmr spectrum of methoxymethane analysis interpretation of chemical shifts ppm spin spin line splitting diagram H1 H-1 nmr for dimethyl ether explaining spin-spin coupling for line splitting doc brown's advanced organic chemistry revision notes

TMS is the acronym for tetramethylsilane, formula Si(CH3)4, whose protons are arbitrarily given a chemical shift of 0.0 ppm. This is the 'standard' in 1H NMR spectroscopy and all other proton resonances, called chemical shifts, are measured with respect to the TMS, and depend on the individual (electronic) chemical environment of the hydrogen atoms in an organic molecule - methoxymethane here.

The chemical shifts quoted in ppm on the diagram of the H-1 NMR spectrum of methoxymethane represent the peaks of the intensity of the chemical shifts of (which are often groups of split lines at high resolution) AND the relative integrated areas under the peaks gives you the ratio of protons in the different chemical environments of the methoxymethane molecule (dimethyl ether).

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 H-1 NMR spectrum of methoxymethane

In terms of spin-spin coupling from the possible proton magnetic orientations, for methoxymethane I have only considered the interactions of non-equivalent protons on adjacent carbon atoms e.g. -CH2-CH3, but this is not possible in methoxymethane.

For the low/high resolution H-1 NMR spectrum of methoxymethane there is only one chemical shift at 3.24 ppm.

Therefore the 6 hydrogen atoms (protons) of methoxymethane occupy the same chemical environment (diagram above for methoxymethane).

CH3OCH3

The one colour indicates the equivalence of all 6 protons in the symmetrical  methoxymethane molecule.

 

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


Number of directly adjacent protons 1H causing splitting Splitting pattern produced from the n+1 rule on spin-spin coupling and the theoretical ratio of line intensities
0 means no splitting             1            
1 creates a doublet           1   1          
2 creates a triplet         1   2   1        
3 creates a quartet       1   3   3   1      
4 creates a quintet     1   4   6   4   1    
5 creates a sextet   1   5   10   10   5   1  
6 creates a septet 1   6   15   20   15   6   1

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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). It is the symmetry of the methoxymethane molecule that results in the chemical equivalence of the methyl groups resulting in a single singlet peak in the 1hH NMR spectrum.

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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Links associated with methoxymethane

H-1 proton NMR spectroscopy index  (Please read 8 points at the top of the 1H NMR index page)

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