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Advanced Organic Chemistry: Carbon-13 NMR spectrum of ethanoic acid

The Carbon-13 NMR spectrum of ethanoic acid (acetic acid)

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 C-13 NMR spectra of ethanoic acid

See also comparing the infrared, mass, 1H and 13C NMR spectra of the isomers of C2H4O2

C-13 nmr spectrum of ethanoic acid analysis of chemical shifts ppm interpretation of C-13 chemical shifts ppm of ethanoic acid 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 - ethanoic acid here.

Ethanoic acid, C2H4O2, (c) doc b , (c) doc b , (c) doc b , (c) doc b

For more see Structure and naming of CARBOXYLIC ACIDS and DERIVATIVES, including isomers

Interpreting the C-13 NMR spectrum of ethanoic acid

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

CH3COOH

(note the colours indicating the 2 different chemical environment of the carbon atoms, the ratio is 1:1).

The two 13C chemical environments of the ethanoic acid molecule are the carbon atom of the methyl group and the carbon atom of the carboxylic acid group.

The carbon-13 NMR spectra provides direct evidence of 2 different chemical environments of the carbon atoms in the ethanoic acid molecule from 2 different chemical shifts (ppm).


Comparing the infrared, mass, 1H NMR and 13C NMR spectra of the 2 isomers of C2H4O2

NOTE: The images are linked to their original detailed spectral analysis pages AND can be doubled in size with touch screens to increase the definition to the original ethanoic acid (acetic acid) and methyl methanoate (methyl formate) image sizes.

INFRARED SPECTRA: Apart from the significant differences in the fingerprint region at wavenumbers 1500 to 400 cm-1, the most striking difference is the broad O-H stretching band ~3200 cm-1, found in the infrared spectrum of carboxylic acids, but absent in the infrared spectrum of esters.

MASS SPECTRA: Apart from the m/z of 60 for the parent molecular ion and m/z 15 ion [CH3]+, both ethanoic acid and methyl methanoate show few similarities in their mass spectra. Their base ion peaks are quite different - for ethanoic acid it is m/z 43 and for methyl methanoate it is m/z 31.

1H NMR SPECTRA: The 1H NMR spectra of ethanoic acid and methyl methanoate are similar with two 'wide-apart' chemical shift singlet peaks in the integrated proton ratio of 3:1 (meaning 2 different 1H chemical environments).

13C NMR SPECTRA: The 13C NMR spectra of ethanoic acid and methyl methanoate are similar, both molecules give two C-13 NMR spectral lines (meaning 2 different 13C chemical environments). The two 13C chemical shifts of ethanoic acid are much closer together.


Key words & phrases: Interpreting the C-13 NMR spectra of ethanoic acid, C-13 nmr spectrum of ethanoic acid, understanding the carbon-13 nmr spectrum of ethanoic acid, explaining the line pattern in the high resolution C-13 nmr spectra of ethanoic acid, revising the C-13 nmr spectrum of ethanoic acid, ppm chemical shifts of the C-13 nmr spectrum of ethanoic acid, how to construct the diagram of the C-13 nmr spectrum of ethanoic acid, how to analyse the chemical shifts in the carbon-13 NMR spectrum of ethanoic acid

Molecular structure diagram of the carbon-13 NMR diagram for the 13C NMR spectrum of ethanoic acid. Deducing the number of different chemical environments of the carbon atoms in the ethanoic acid molecule from the 13C chemical shifts in the carbon-13 NMR spectrum of ethanoic acid. Revision notes on the carbon-13 NMR spectrum of ethanoic acid. Matching and deducing the structure of the ethanoic acid molecule from its 13C NMR spectrum. Carbon-13 NMR spectroscopy of carboxylic acids, 13C NMR spectra of ethanoic acid, an isomer of molecular formula C2H4O2


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The chemistry of CARBOXYLIC ACIDS and DERIVATIVES revision notes INDEX

C-13 NMR spectroscopy index

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