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Advanced Organic Chemistry: 1H NMR spectrum of 1-methylethyl methanoate

Interpreting the 1H NMR spectrum of 1-methylethyl 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 1-methylethyl methanoate

1H proton nmr spectrum of 1-methylethyl methanoate low/high resolution diagrams C4H8O2 HCOOCH(CH3)2 analysis interpretation of chemical shifts ppm spin spin line splitting diagram H1 H-1 nmr for isopropyl 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 - 1-methylethyl methanoate here.

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

HCOOCH(CH3)2  1-methylethyl methanoate, propan-2-yl methanoate,

is an example of an ester, some old names: isopropyl methanoate, isopropyl formate

Interpreting the H-1 NMR spectrum of 1-methylethyl methanoate

In terms of spin-spin coupling from the possible proton magnetic orientations, for 1-methylethyl methanoate I have only considered the interactions of non-equivalent protons on adjacent carbon atoms e.g. -CH-CH3 protons.

For relatively simple molecules, the low resolution H-1 NMR spectrum of 1-methylethyl methanoate is a good starting point (just 'blur' the high resolution diagram above to see the proton ratio of 1:1:6.

The hydrogen atoms (protons) of 1-methylethyl 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 1-methylethyl methanoate).

HCOOCH(CH3)2

Note the proton ratio 1:1:6 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 1-methylethyl methanoate.

Although there are 8 hydrogen atoms in the molecule, there are only 8 possible different chemical environments for the hydrogen atoms in 1-methylethyl methanoate molecule.

The integrated signal proton ratio 1:1:6 observed in the high resolution H-1 NMR spectrum, corresponds with the structural formula of 1-methylethyl methanoate.

The high resolution 1H NMR spectrum of 1-methylethyl methanoate

The ppm quoted on the diagram represent the peak of resonance intensity for a particular proton group in the molecule of 1-methylethyl 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 1-methylethyl methanoate below.

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

(a) 1H Chemical shift 8.02 ppm, H-C=O proton: HCOOCH(CH3)2

This 1H NMR resonance is a singlet, the are no protons on an adjacent atom, so no splitting occurs.

Evidence for the presence of an isolated proton in the molecule of 1-methylethyl methanoate

(b) 1H Chemical shift 5.14 ppm, CH proton: HCOOCH(CH3)2

This 1H NMR resonance is split into a 1:6:15:20:15:6:1 by the six methyl protons (n+1 = 7).

Evidence for the presence of a  CH3-CHx-CH3 grouping in the molecule of 1-methylethyl methanoate

(c) 1H Chemical shift 1.28 ppm, methyl protons: HCOOCH(CH3)2

This 1H NMR resonance is split into a 1:1 doublet by the CH proton (n+1 = 2).

Evidence for the presence of a CH group in the molecule of 1-methylethyl methanoate

Note the decreasing effect on the 1H chemical shift as the proton of the alkyl group is further from the more electronegative oxygen atoms of 1-methylethyl 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

Key words & phrases: C4H8O2 HCOOCH(CH3)2 Interpreting the proton H-1 NMR spectra of 1-methylethyl methanoate, low resolution & high resolution proton nmr spectra of 1-methylethyl methanoate, H-1 nmr spectrum of 1-methylethyl methanoate, understanding the hydrogen-1 nmr spectrum of 1-methylethyl methanoate, explaining the line splitting patterns from spin-spin coupling  in the high resolution H-1 nmr spectra of 1-methylethyl methanoate, revising the H-1 nmr spectrum of 1-methylethyl methanoate, proton nmr of 1-methylethyl methanoate, ppm chemical shifts of the H-1 nmr spectrum of 1-methylethyl methanoate, explaining and analyzing spin spin line splitting in the H-1 nmr spectrum, how to construct the diagram of the H-1 nmr spectrum of 1-methylethyl methanoate, how to work out the number of chemically different protons in the structure of the 1-methylethyl methanoate organic molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR spectrum of 1-methylethyl methanoate using the n+1 rule to explain the spin - spin coupling ine splitting in the proton nmr spectrum of 1-methylethyl methanoate deducing the nature of the protons from the chemical shifts ppm in the H-1 nmr spectrum of 1-methylethyl methanoate examining the 1H nmr spectrum of  1-methylethyl methanoate analysing the 1-H nmr spectrum of 1-methylethyl methanoate how do you sketch and interpret the H-1 NMR spectrum of 1-methylethyl methanoate interpreting interpretation of the 1H proton spin-spin coupling causing line splitting in the NMR spectrum of 1-methylethyl methanoate  assignment of chemical shifts in the proton 1H NMR spectrum of 1-methylethyl methanoate formula explaining spin-spin coupling for line splitting for 1-methylethyl methanoate propan-2-yl methanoate isopropyl methanoate, isopropyl formate


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