Advanced pre-university Organic Chemistry:  1H NMR spectrum of 3-hydroxybutanone

Interpreting and explaining the H-1 hydrogen-1 (proton) NMR spectrum of 3-hydroxybutanone  (acetoin)

[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 spectrometry - analysing the 1H NMR spectra of 3-hydroxybutanone [spectra page updated April 3rd 2026 *]

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Introductory note on the 1H NMR spectra of 3-hydroxybutanone

Students and teachers please note my explanation of the proton NMR spectrum of 3-hydroxybutanone is designed for advanced, but pre-university, chemistry courses.

The chemical shift δ splitting pattern effects for 3-hydroxybutanone are confined to a proton spin-spin coupling effects analysed using the n+1 rule for adjacent non-equivalent proton fields (n is the number of neighbouring protons in a non-equivalent different chemical environment for the 3-hydroxybutanone molecule).

It is assumed that the integrated intensities of the δ chemical shifts give the ratio of the protons in the different non-equivalent chemical environments of the 3-hydroxybutanone molecule.

The most common solvent used for investigating the 1H NMR spectrum of compounds like 3-hydroxybutanone, is CDCl3 and other deuterated solvents to avoid confusion with a 1H NMR signal, 2D (2H) has a different chemical shift.

1H proton nmr spectrum of 3-hydroxybutanone low/high resolution diagrams C4H8O2 CH3COCH(OH)CH3 analysis interpretation of chemical shifts ppm spin spin line splitting diagram H1 H-1 nmr for acetoin explaining spin-spin coupling for line splitting 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 resonances, called chemical shifts, are measured with respect to the TMS, and depend on the individual (electronic) chemical environment of the hydrogen atoms in an organic molecule - 3-hydroxybutanone here.

The chemical shifts quoted in ppm on the diagram of the H-1 NMR spectrum of 3-hydroxybutanone 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 3-hydroxybutanone molecule.

C4H8O2, 3-hydroxybutanone 3-hydroxybutan-2-one acetoin CH3COCH(OH)CH3 C4H8O2, 3-hydroxybutanone, 3-hydroxybutan-2-one, 'acetoin', CH3COCH(OH)CH3

The molecular structure and naming of aliphatic alcohols

The molecular structure and naming of aldehydes and ketones

Interpreting the H-1 NMR spectrum of 3-hydroxybutanone

In terms of spin-spin coupling from the possible proton magnetic orientations, for 3-hydroxybutanone I have only considered the interactions of non-equivalent protons on adjacent carbon atoms e.g. -CH-CH3, protons, but note that the hydroxyl proton (O-H) resonance is not split (singlet) and neither does this proton cause splitting in the CH or CH3 protons.

For relatively simple molecules, the low resolution H-1 NMR spectrum of 3-hydroxybutanone is a good starting point (low resolution diagram above).

The hydrogen atoms (protons) of 3-hydroxybutanone occupy 4 different chemical environments so that the low or low resolution NMR spectra should show 4 principal 1H peaks of different H-1 NMR chemical shifts in the integrated proton ratio of 3:1:1:3 (diagram above for 3-hydroxybutanone).

CH3COCH(OH)CH3

Note the proton ratio 3:1:1:3 of the 4 colours of the protons in the 4 chemically different proton environments

Chemical shifts (a) to (d) on the H-1 NMR spectrum diagram for 3-hydroxybutanone.

Although there are 8 hydrogen atoms in the molecule, there are only 4 possible different chemical environments for the hydrogen atoms in 3-hydroxybutanone molecule.

The integrated signal proton ratio 3:1:1:3 observed in the high resolution H-1 NMR spectrum, corresponds with the structural formula of 3-hydroxybutanone.

The high resolution 1H NMR spectrum of 3-hydroxybutanone

The high resolution spectra of 3-hydroxybutanone shows 4 groups of proton resonances and in the 3:1:1:3 ratio expected from the structural formula of 3-hydroxybutanone.

The ppm quoted on the diagram represent the peak of resonance intensity for a particular proton group in the molecule of 3-hydroxybutanone - since the peak' is at the apex of a band of H-1 NMR resonances due to spin - spin coupling field splitting effects - see high resolution notes on 3-hydroxybutanone below.

So, using the chemical shifts and applying the n+1 rule to 3-hydroxybutanone and make some predictions using some colour coding! (In problem solving you work the other way round!)

(a) 1H Chemical shift 2.21 ppm, methyl protons: CH3COCH(OH)CH3

This 1H NMR resonance appears as a singlet because there are no non-equivalent protons on the adjacent carbon atom.

From the proton ratio, evidence for the presence of an 'isolated' alkyl group (likely to be a methyl group) in the molecule of 3-hydroxybutanone

(b) 1H Chemical shift 4.26 ppm, CH proton: CH3COCH(OH)CH3

This 1H NMR resonance is split by the adjacent methyl protons into 1 1:3:1: quartet (n+1 = 4).

Evidence for the presence of a CH3 group in the molecule of 3-hydroxybutanone

(c) 1H Chemical shift 3.65 ppm: CH3COCH(OH)CH3

This 1H NMR resonance appears as a singlet because there is no interaction observed with the CH proton.

Evidence for the presence of an 'isolated' proton in the molecule of 3-hydroxybutanone

If the 1H NMR spectrum of 3-hydroxbutanone is done with deuterium oxide solvent (D2O) this signal is removed from it because D (2H) has a completely different chemical shift compared to that of 1H protons.

See extra note at the end.

(d) 1H Chemical shift 1.39 ppm: CH3COCH(OH)CH3

This 1H NMR resonance is split by the adjacent CH proton into 1 1:1: doublet (n+1 = 2).

Evidence for the presence of a CH3 group in the molecule of 3-hydroxybutanone

From the proton ratio, evidence for the presence of a 2nd CH3 group in the molecule of 3-hydroxybutanone

An important note about the hydroxyl group on butan-2-ol (for pre-university students):

Unless the alcohol is completely free of water (difficult), the hydrogen on the -O-H hydroxyl group and any hydrogens on the adjacent carbon atoms do not interact to produce any spin-spin splitting. Therefore the -OH peak shows up as a singlet and you don't usually have to consider its effect on any hydrogen atoms, if present on the adjacent carbon atom (C-OH), and, neither do you have to consider the splitting effect of adjacent C-H protons on the hydrogen of the OH group.

EXTRA NOTE on why the OH proton chemical shift is usually observed as a singlet in alcohols like xyz and how deuterium oxide can be used to identify the peak caused by the hydroxyl proton

Although extremely weak acids, there is constant exchanging of protons between alcohol molecules (R = alkyl groups of xyz).

R-O-H  +  H-O-R    R-O-H  +  H-O-R

The rate of proton transfer is increased by traces of water.

R-O-H  +  H-O-H    R-O-H  +  H-O-H

This cannot happen with the non-acidic C-H protons of alkyl groups in alcohols like xyz.

This rapid proton transfer interferes with the field splitting effects of the hydroxyl O-H protons and carbon C-H protons and the spin-spin coupling effects disappears if enough deuterium oxide is present.

This phenomena can be used to identify the O-H proton resonance in alcohols from other C-H proton resonances in hydroxyl molecules like xyz.

If deuterium oxide (D2O, where D = 2H) is added to the NMR alcohol sample, the 1H protons are rapidly replaced by 2H protons in the xyz molecule.

R-O-H  +  D-O-D    R-O-D  +  H-O-D

The 2H chemical shift frequency is different to the 1H chemical shift frequency, so the effect of D2O is to remove (or reduce intensity of) the chemical shift for the OH proton from the 1H NMR spectrum of xyz, thereby identifying the original 1H chemical shift as belonging to the hydroxyl group O-H proton and not a C-H proton of the xyz molecule.

The splitting pattern from proton spin-spin coupling effects is analysed using the n+1 rule for adjacent non-equivalent proton fields (n is the number of neighbouring protons in a non-equivalent different chemical environment) and applied to the 1H NMR spectrum of 3-hydroxybutanone.
Number of directly adjacent protons 1H causing splitting Splitting pattern produced from the n+1 rule on spin-spin coupling 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

Key words & phrases: C4H8O2 CH3COCH(OH)CH3 Interpreting the proton H-1 NMR spectra of 3-hydroxybutanone, low resolution & high resolution proton nmr spectra of 3-hydroxybutanone, H-1 nmr spectrum of 3-hydroxybutanone, understanding the hydrogen-1 nmr spectrum of 3-hydroxybutanone, explaining the line splitting patterns from spin-spin coupling  in the high resolution H-1 nmr spectra of 3-hydroxybutanone, revising the H-1 nmr spectrum of 3-hydroxybutanone, proton nmr of 3-hydroxybutanone, ppm chemical shifts of the H-1 nmr spectrum of 3-hydroxybutanone, explaining and analyzing spin spin line splitting in the H-1 nmr spectrum, how to construct the diagram of the H-1 nmr spectrum of 3-hydroxybutanone, how to work out the number of chemically different protons in the structure of the 3-hydroxybutanone organic molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR spectrum of 3-hydroxybutanone using the n+1 rule to explain the spin - spin coupling ine splitting in the proton nmr spectrum of 3-hydroxybutanone deducing the nature of the protons from the chemical shifts ppm in the H-1 nmr spectrum of 3-hydroxybutanone examining the 1H nmr spectrum of  3-hydroxybutanone analysing the 1-H nmr spectrum of 3-hydroxybutanone how do you sketch and interpret the H-1 NMR spectrum of 3-hydroxybutanone interpreting interpretation of the 1H proton spin-spin coupling causing line splitting in the NMR spectrum of 3-hydroxybutanone  assignment of chemical shifts in the proton 1H NMR spectrum of 3-hydroxybutanone formula explaining spin-spin coupling for line splitting for 3-hydroxybutanone old names functional group 3-hydroxybutan-2-one acetoin How do you interpret the H-1 NMR spectrum of 3-hydroxybutanone How to interpret the H-1 NMR spectrum of 3-hydroxybutanone Explanatory diagram of the chemical shifts of the 1H H-1 proton NMR spectrum of the 3-hydroxybutanone molecule in terms of its molecular structure. Listing data of all the chemical shift peaks in ppm in the proton NMR spectrum of 3-hydroxybutanone. How to explain the H-1 NMR spectrum of 3-hydroxybutanone. The chemical shifts and  integrated values of the proton ratios in the 1-H NMR spectrum of the 3-hydroxybutanone molecule. How to work out the molecular structure of the 3-hydroxybutanone molecule from its proton NMR spectrum. The uses and distinctive features of the proton NMR spectrum of the 3-hydroxybutanone molecule explained. What does the H-1 proton NMR spectrum chemical shifts tell us about the structure and properties of the 3-hydroxybutanone molecule? explaining the spin-spin proton coupling effects in the 1H NMR spectrum of 3-hydroxybutanone. interpretation diagram explaining the proton splitting pattern produced from the n+1 rule and the theoretical ratio of chemical shift δ and values of intensities for the proton NMR spectrum lines of 3-hydroxybutanone

Links associated with 3-hydroxybutanone

The mass spectrum of 3-hydroxybutanone (3-hydroxybutan-2-one, 'acetoin')

The C-13 spectrum of 3-hydroxybutanone (3-hydroxybutan-2-one, 'acetoin')

The infrared spectrum of 3-hydroxybutanone (3-hydroxybutan-2-one, 'acetoin')

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Website content © Dr Phil Brown 2000+. All copyrights reserved on revision notes, images, quizzes, worksheets etc. Copying of Doc Brown's pre-university advanced level chemistry website material is NOT permitted. Exam revision summaries & references to science course specifications are unofficial. These organic chemistry revision notes on spectroscopy (1H NMR spectra of 3-hydroxybutanone, 3-hydroxybutan-2-one (acetoin)) are suitable for use of pre-university students studying AQA advanced level chemistry, Edexcel advanced level chemistry, OCR advanced level chemistry, IB advanced level chemistry, WJEC (Eduqas) advanced level chemistry, CIE advanced level chemistry, CCEA advanced level chemistry, US grade 11-12 AP honors chemistry courses and they will also prove useful to 1st year undergraduate students of chemistry.

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