Advanced Organic Chemistry: Carbon-13 NMR spectrum of ethanoic acid CH3COOH

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Interpreting the carbon-13 NMR spectrum of ethanoic acid (acetic acid) CH3COOH (re-edit)

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

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Links associated with ethanoic acid

C-13 NMR spectroscopy - spectra index

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.

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Links associated with ethanoic acid

The infrared spectrum of Ethanoic acid (acetic acid)

The mass spectrum of Ethanoic acid (acetic acid)

The H-1 NMR spectrum of Ethanoic acid (acetic acid)

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C-13 NMR spectroscopy index

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