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Advanced Organic Chemistry: 1H NMR spectrum of ethyl methanoate (ethyl formate)

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

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 ethyl methanoate

1H proton nmr spectrum of ethyl methanoate low/high resolution diagrams C3H6O2 HCOOCH2CH3 analysis interpretation of chemical shifts ppm spin spin line splitting diagram H1 H-1 nmr for ethyl formate 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 - ethyl methanoate here.

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

Ethyl methanoate (ethyl formate) C3H6O2  (c) doc b  (c) doc b  (c) doc b  (c) doc b

Interpreting the H-1 NMR spectrum of ethyl methanoate

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

For relatively simple molecules, the low resolution H-1 NMR spectrum of ethyl methanoate is a good starting point, you would expect to see three principal peaks in the ratio 1:2:3 (just 'blur' the high resolution diagram above!).

The hydrogen atoms (protons) of ethyl methanoate 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 ethyl methanoate).

HCOOCH2CH3

Note the proton ratio 1:2:3 of the 3 colours of the protons in the 3 chemically different proton environments

Chemical shifts (a) to (c) on the H-1 NMR spectrum diagram for ethyl methanoate.

Although there are 6 hydrogen atoms in the molecule, there are only 3 possible different chemical environments for the hydrogen atoms in ethyl methanoate molecule.

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

The high resolution 1H NMR spectrum of ethyl methanoate

All low and high resolution spectra of ethyl methanoate show 3 groups of proton resonances and in the : HCOOCH2CH3 ratio expected from the structural formula of ethyl methanoate.

The ppm quoted on the diagram represent the peak of resonance intensity for a particular proton group in the molecule of ethyl methanoate - 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 ethyl methanoate below.

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

(a) 1H Chemical shift 8.03 ppm, lone hydrogen atom : HCOOCH2CH3

This 1H resonance is NOT split by any other proton magnetic field - a singlet resonance spectral line.

There are no protons on an adjacent atom to cause spin - spin coupling.

Evidence for the presence of a 'lone' proton in the molecule of ethyl methanoate

(b) 1H Chemical shift 4.22 ppm, CH2 protons: HCOOCH2CH3

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

Evidence for the presence of a CH3 group in the molecule of ethyl methanoate

(c) 1H Chemical shift 1.29 ppm, methyl protons: HCOOCH2CH3

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

Evidence for the presence of a CH2 group in the molecule of ethyl methanoate

Note the decreasing effect on the 1H chemical shift as the proton (in the ethyl group) is further from the more electronegative oxygen atoms in ethyl methanoate.


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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