C-13 nmr spectrum of ethanal analysis of chemical shifts ppm interpretation of C-13 chemical shifts ppm of acetaldehyde C13 13-C nmr doc brown's advanced organic chemistry revision notes

Advanced Organic Chemistry: Carbon-13 NMR spectrum of ethanal CH₃CHO

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Interpreting the Carbon-13 NMR spectrum of ethanal (acetaldehyde)

[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 analysis of ethanal [spectra page updated Mar 23rd 2026 *]

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C-13 NMR spectroscopy - spectra index

Introductory note on the 13C NMR spectrum of ethanal

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

The description does not involve the chemical shift δ spin-spin coupling effects for ethanal 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 ethanal molecule.

The most common solvent used for investigating the C13 NMR spectrum of compounds like ethanal, is CDCl₃ and other deuterated solvents.

C-13 nmr spectrum of ethanal analysis of chemical shifts ppm interpretation of C-13 chemical shifts ppm of acetaldehyde 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 shifts, called chemical shifts, depend on the individual (electronic) chemical environment of the ¹³C atoms in an organic molecule - ethanal here.

Ethanal (acetaldehyde), C₂H₄O, , , , an aliphatic aldehyde
The molecular structure and naming of aldehydes and ketones
Interpreting the C-13 NMR spectrum of ethanal

As you can see from the diagram above there are 2 different chemical shift lines in the C-13 NMR spectrum of ethanal indicating 2 different chemical environments of the carbon atoms.

CH₃CHO

(Note the 2 colours indicating the 2 different chemical environment of the carbon atoms in ethanal).

Note the decreasing effect on the chemical shift as the carbon atom is further from the highly electronegative oxygen atom of ethanal.

The carbon attached to the very electronegative oxygen atom of the aldehyde group tends have a higher chemical shift than the carbon atom of an alkyl group, quite a contrast.

The carbon-13 NMR spectra a provides direct evidence of 2 different carbon atom environments in the ethanal molecule from 2 different chemical shifts (ppm).

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Links associated with ethanal

The infrared spectrum of ethanal (acetaldehyde)

The mass spectrum of ethanal (acetaldehyde)

The H-1 NMR spectrum of ethanal (acetaldehyde)

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