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Advanced Organic Chemistry: 1H NMR spectrum of methoxyethane

Interpreting the H-1 hydrogen-1 (proton) NMR spectrum of methoxyethane

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 methoxyethane

C3H8O CH3OCH2CH3 low and high resolution 1H proton nmr spectrum of methoxyethane analysis interpretation of chemical shifts ppm spin spin line splitting diagram H1 H-1 nmr for ethyl methyl 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 - methoxyethane here.

The chemical shifts quoted in ppm on the diagram of the H-1 NMR spectrum of methoxyethane 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 methoxyethane molecule.

Methoxyethane  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

Interpreting the H-1 NMR spectrum of methoxyethane

In terms of spin-spin coupling from the possible proton magnetic orientations, for methoxyethane I have only considered the interactions of non-equivalent protons on adjacent carbon atoms e.g. -CH2-CH3 protons here.

For relatively simple molecules, the low resolution H-1 NMR spectrum of methoxyethane is a good starting point (low resolution diagram above) from which you can deduce ....

,,, the hydrogen atoms (protons) of methoxyethane occupy 3 different chemical environments so that the low resolution NMR spectra should show 3 principal peaks of different H-1 NMR chemical shifts (diagram above for methoxyethane).

CH3OCH2CH3

Note the proton ratio 3:2:3 of the three colours of the protons in the three chemically different environments.  Chemical shifts (b), (a) and (c) on the H-1 NMR spectrum diagram for methoxyethane.

Although there are 8 hydrogen atoms in the molecule, there are only 3 possible different chemical environments for the hydrogen atoms in methoxyethane molecule.

The integrated signal proton ratio 3:2:3 observed in the high resolution H-1 NMR spectrum, corresponds with the structural formula of methoxyethane.

The high resolution 1H NMR spectrum of methoxyethane

All low and high resolution spectra of methoxyethane show 3 groups of proton resonances and in the 3:2:3 ratio expected from the formula of methoxyethane.

The ppm quoted on the diagram represent the peak of resonance intensity for a particular proton group in the molecule of methoxyethane - since the peak' is at the apex of a band of H-1 NMR resonances due to spin - spin coupling field splitting effects - see high resolution notes on methoxyethane below.

So, using the chemical shifts and applying the n+1 rule to methoxyethane and make some predictions using some colour coding! (In problem solving you work the other way round!)

(a) 1H Chemical shift of methyl protons 3.25 ppm: CH3OCH2CH3

This proton resonance is not split by other protons - non are on an adjacent carbon atoms, so just a singlet is observed,

Evidence for the presence of an alkyl group not connected to another atom with protons bonded to it in the molecule of methoxyethane

(b) 1H Chemical shift of CH2 protons 3.52 ppm: CH3OCH2CH3

This proton resonance is split into a 1:3:3:1 quartet by the adjacent methyl protons (n+1 = 4).

Evidence for the presence of a methyl group in the molecule of methoxyethane

(c) 1H Chemical shift of methyl protons 1.42 ppm: CH3OCH2CH3

This proton resonance is split into a 1:2:1 triplet by the adjacent CH2 protons (n+1 = 3).

Evidence for the presence of a CH2 group in the molecule of methoxyethane

Note the decreasing effect on the 1H chemical shift as the proton is further from the more electronegative oxygen atom in methoxyethane.


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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