Advanced pre-university Organic Chemistry:  1H NMR spectrum of propanoic acid CH3CH2COOH

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Interpreting and explaining the H-1 proton NMR spectrum of propanoic acid (propionic acid)

[Author © Dr Phil Brown PhD: Doc Brown's advanced level organic chemistry exam revision notes suitable for students of UK A level chemistry courses & US K12 grade 11, grade 12 and AP honors chemistry courses: Molecular spectroscopy - analysing the mass spectra of propanoic acid [spectra page updated April 4th 2026 *]

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 H-1 proton NMR spectroscopy - spectra index

Introductory note on the 1H NMR spectra of propanoic acid

Students and teachers please note my explanation of the proton NMR spectrum of propanoic acid is designed for advanced, but pre-university, chemistry courses.

The chemical shift δ splitting pattern effects for propanoic acid are confined to a proton spin-spin coupling effects analysed using the n+1 rule for adjacent non-equivalent proton fields (n is the number of neighbouring protons in a non-equivalent different chemical environment for the propanoic acid molecule).

It is assumed that the integrated intensities of the δ chemical shifts give the ratio of the protons in the different non-equivalent chemical environments of the propanoic acid molecule.

The most common solvent used for investigating the 1H NMR spectrum of compounds like propanoic acid, is CDCl3 and other deuterated solvents to avoid confusion with a 1H NMR signal, 2D (2H) has a different chemical shift.

1H proton nmr spectrum of propanoic acid low/high resolution diagrams C3H6O2 CH3CH2COOH analysis interpretation of chemical shifts ppm spin spin line splitting diagram H1 H-1 nmr for propionic acid 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 - propanoic acid here.

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

Propanoic acid  (propionic acid) C3H6O2   (c) doc b   (c) doc b   (c) doc b

The molecular structure and naming of carboxylic acids and derivatives

Interpreting the H-1 NMR spectrum of propanoic acid

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

For relatively simple molecules, the low resolution H-1 NMR spectrum of propanoic acid is a good starting point (high resolution diagram above, but just imagine 3 'unsplit' peaks and with an integrated proto ratio of 1:2:3 from left to right).

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

CH3CH2COOH

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

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

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

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

The high resolution 1H NMR spectrum of propanoic acid

All low and high resolution spectra of propanoic acid show 3 groups of proton resonances and in the 3:2:1 ratio expected from the formula of propanoic acid.

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

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

(a) 1H Chemical shift 1.16 ppm, methyl protons: CH3CH2COOH

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

Evidence for the presence of a CH2 group in the molecule of propanoic acid

(b) 1H Chemical shift 2.38 ppm, CH2 protons: CH3CH2COOH

This 1H resonance is split by the CH3 protons into a 1:3:3:1 quartet (n+3 = 4).

Evidence for the presence of a CH3 group in the molecule of propanoic acid

(c) 1H Chemical shift 11.7 ppm, the hydroxyl group proton: CH3CH2COOH

This 1H resonance is NOT split because there are no protons on the adjacent carbon atom.

Evidence for the presence of an 'isolated' proton e.g. in a -COOH  group with no adjacent carbon atom attached to a proton (as in the molecule of propanoic acid or any other carboxylic acid).

Note the decreasing effect on the 1H chemical shift as the proton is further from the more electronegative oxygen atoms in propanoic acid.

Note the particularly large chemical shift for the proton of the hydroxyl group with

EXTRA NOTE on why the OH proton chemical shift is usually observed as a singlet in carboxylic acids like propanoic acid and how deuterium oxide can be used to identify the peak caused by the hydroxyl proton

Although extremely weak acids, there is constant exchanging of protons between carboxylic acid molecules (R = alkyl groups of propanoic acid or just the 'rest of the molecule).

R-O-H  +  H-O-R    R-O-H  +  H-O-R

The rate of proton transfer is increased by traces of water.

R-O-H  +  H-O-H    R-O-H  +  H-O-H

This cannot happen with the non-acidic C-H protons of alkyl groups in carboxylic acids like propanoic acid.

This rapid proton transfer interferes with the field splitting effects of the hydroxyl O-H protons and carbon C-H protons and the spin-spin coupling effects disappears if enough deuterium oxide is present.

This phenomena can be used to identify the O-H proton resonance in carboxylic acids from other C-H proton resonances in hydroxyl molecules like propanoic acid.

If deuterium oxide (D2O, where D = 2H) is added to the NMR alcohol sample, the 1H protons are rapidly replaced by 2H protons in the propanoic acid molecule.

R-O-H  +  D-O-D    R-O-D  +  H-O-D

The 2H chemical shift frequency is different to the 1H chemical shift frequency, so the effect of D2O is to remove (or reduce intensity of) the chemical shift for the OH proton from the 1H NMR spectrum of propanoic acid, thereby identifying the original 1H chemical shift as belonging to the hydroxyl group O-H proton and not a C-H proton of the propanoic acid molecule.

The splitting pattern from proton spin-spin coupling effects is analysed using the n+1 rule for adjacent non-equivalent proton fields (n is the number of neighbouring protons in a non-equivalent different chemical environment) and applied to the 1H NMR spectrum of propanoic acid.
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: C3H6O2 CH3CH2COOH Interpreting the proton H-1 NMR spectra of propanoic acid, low resolution & high resolution proton nmr spectra of propanoic acid, H-1 nmr spectrum of propanoic acid, understanding the hydrogen-1 nmr spectrum of propanoic acid, explaining the line splitting patterns from spin-spin coupling  in the high resolution H-1 nmr spectra of propanoic acid, revising the H-1 nmr spectrum of propanoic acid, proton nmr of propanoic acid, ppm chemical shifts of the H-1 nmr spectrum of propanoic acid, 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 propanoic acid, how to work out the number of chemically different protons in the structure of the propanoic acid organic molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR spectrum of propanoic acid using the n+1 rule to explain the spin - spin coupling ine splitting in the proton nmr spectrum of propanoic acid deducing the nature of the protons from the chemical shifts ppm in the H-1 nmr spectrum of propanoic acid examining the 1H nmr spectrum of  propanoic acid analysing the 1-H nmr spectrum of propanoic acid how do you sketch and interpret the H-1 NMR spectrum of propanoic acid interpreting interpretation of the 1H proton spin-spin coupling causing line splitting in the NMR spectrum of propanoic acid  assignment of chemical shifts in the proton 1H NMR spectrum of propanoic acid formula explaining spin-spin coupling for line splitting for propionic acid How do you interpret the H-1 NMR spectrum of propanoic acid How to interpret the H-1 NMR spectrum of propanoic acid Explanatory diagram of the chemical shifts of the 1H H-1 proton NMR spectrum of the propanoic acid molecule in terms of its molecular structure. Listing data of all the chemical shift peaks in ppm in the proton NMR spectrum of propanoic acid. How to explain the H-1 NMR spectrum of propanoic acid. The chemical shifts and  integrated values of the proton ratios in the 1-H NMR spectrum of the propanoic acid molecule. How to work out the molecular structure of the propanoic acid molecule from its proton NMR spectrum. The uses and distinctive features of the proton NMR spectrum of the propanoic acid molecule explained. What does the H-1 proton NMR spectrum chemical shifts tell us about the structure and properties of the propanoic acid molecule? explaining the spin-spin proton coupling effects in the 1H NMR spectrum of propanoic acid. interpretation diagram explaining the proton splitting pattern produced from the n+1 rule and the theoretical ratio of chemical shift δ and values of intensities for the proton NMR spectrum lines of propanoic acid

Links associated with propanoic acid

The infrared spectrum of propanoic acid (propionic acid)

The mass spectrum of propanoic acid (propionic acid)

The C-13 NMR spectrum of propanoic acid (propionic acid)

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

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