Advanced pre-university Organic Chemistry:  13C NMR spectrum of propanoic acid CH3CH2COOH

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Interpreting and explaining the Carbon-13 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 1H NMR spectra of propanoic acid [spectra page updated April 4th 2026 *]

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 C-13 NMR spectroscopy - spectra index

Introductory note on the 13C NMR spectrum of propanoic acid

Students and teachers please note that my explanation of the carbon-13 NMR spectrum of propanoic acid is designed for advanced, but pre-university, chemistry courses.

The description does not involve the chemical shift δ spin-spin coupling effects for propanoic acid and the relative size of the carbon-13 NMR shifts does not give the ratio of the carbon atoms in the different non-equivalent chemical environments of the propanoic acid molecule.

The most common solvent used for investigating the 13C NMR spectrum of compounds like propanoic acid, is CDCl3 and other deuterated solvents.

13C nmr spectrum of propanoic acid C3H6O2 CH3CH2COOH analysis of chemical shifts ppm interpretation of C-13 chemical shifts ppm of propionic acid C13 13-C nmr doc brown's advanced organic chemistry revision notes 

TMS is the acronym for tetramethylsilane, formula Si(CH3)4, whose 13C atoms are arbitrarily given a chemical shift of 0.0 ppm. This is the 'standard' in 13C NMR spectroscopy and all other 13C resonances, called chemical shifts, are measured with respect to the TMS, and depend on the individual (electronic) chemical environment of the 13C atoms in an organic molecule - propanoic acid here.

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 C-13 NMR spectrum of propanoic acid

As you can see from the diagram above there are 3 different 13C chemical shift lines in the C-13 NMR spectrum of propanoic acid indicating 3 different chemical environments of the 3 carbon atoms of propanoic acid.

CH3CH2COOH

(Note the 3 different colours indicating the 3 different chemical environments of the 3 carbon atoms in propanoic acid).

13C chemical shifts (a) to (c) on the C-13 NMR spectrum diagram for propanoic acid.

Note the decreasing effect on the 13C chemical shift as the carbon atom is further from the more electronegative oxygen atoms in propanoic acid.

The carbon-13 NMR spectra provides direct evidence of 3 different carbon atom chemical environments for the 3 carbon atoms in the propanoic acid molecule, deduced from the presence of 3 different 13C NMR chemical shifts (ppm).

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Links associated with propanoic acid

The infrared spectrum of propanoic acid (propionic acid)

The mass spectrum of propanoic acid (propionic acid)

The H-1 NMR spectrum of propanoic acid (propionic acid)

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