ethanoic acid low high resolution H-1 proton nmr spectrum of ethanoic acid analysis interpretation of chemical shifts ppm spin spin line splitting doc brown's advanced organic chemistry revision notes

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Advanced Organic Chemistry: H-1 NMR spectrum of ethanoic acid

The H-1 hydrogen-1 (proton) 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 H-1 NMR spectra of ethanoic acid

low and high resolution H-1 proton nmr spectrum of ethanoic acid analysis interpretation of chemical shifts ppm spin spin line splitting diagram 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 shifts, called chemical shifts, depend on the individual (electronic) chemical environment of the hydrogen atoms in an organic molecule - ethanoic acid here.

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

Ethanoic acid C₂H₄O₂ , , ,

Interpreting the H-1 NMR spectrum of ethanoic acid

For relatively simple molecules, the low resolution H-1 NMR spectrum of ethanoic acid is a good starting point.

The hydrogen atoms (protons) of ethanoic acid occupy 2 different chemical environments so that the H-1 proton low resolution NMR spectra should show principal 2 peaks in the ratio 3 : 1 (diagram above).

CH₃COOH

(note the 3: 1 ratio of the 2 colours of the protons indicating the 2 chemically different environments)

The proton ratio observed of 3:1, corresponds with the structural formula of ethanoic acid.

There is no need to consider the very high resolution spectrum of ethanoic acid, there are no other immediate protons adjacent to the H or OH or the H's of the CH₃ group so the spin-spin splitting lines would be very weak.

Number of protons ¹H causing splitting	Splitting pattern produced from the n+1 rule 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

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