Advanced Organic Chemistry: 1H NMR spectrum of 2-methylpropanoic acid (CH3)2CHCOOH

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Interpreting and explaining the 1H NMR spectrum of 2-methylpropanoic acid (isobutyric acid)

[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 2-methylpropanoic acid (1H NMR spectra) [spectra page updated April 3rd 2026 *]

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 H-1 proton NMR spectroscopy - spectra index

Introductory note on the 1H NMR spectra of 2-methylpropanoic acid

Students and teachers please note my explanation of the proton NMR spectrum of 2-methylpropanoic acid is designed for advanced, but pre-university, chemistry courses.

The chemical shift δ splitting pattern effects for 2-methylpropanoic acid 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 2-methylpropanoic acid 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 2-methylpropanoic acid molecule.

The most common solvent used for investigating the 1H NMR spectrum of compounds like 2-methylpropanoic acid, 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 2-methylpropanoic acid low/high resolution diagrams C4H8O2 (CH3)2CHCOOH analysis interpretation of chemical shifts ppm spin spin line splitting diagram H1 H-1 nmr for isobutyric acid 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 - 2-methylpropanoic acid here.

The chemical shifts quoted in ppm on the diagram of the H-1 NMR spectrum of 2-methylpropanoic 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 2-methylpropanoic acid molecule.

2-methylpropanoic acid (isobutyric acid), C4H8O2  (c) doc b   (c) doc b   (c) doc b

The molecular structure and naming of carboxylic acids and derivatives

Interpreting the H-1 NMR spectrum of 2-methylpropanoic acid

In terms of spin-spin coupling from the possible proton magnetic orientations, for 2-methylpropanoic acid I have only considered the interactions of non-equivalent protons on adjacent carbon atoms e.g. -CH-CH3 protons.

For relatively simple molecules, the low resolution H-1 NMR spectrum of 2-methylpropanoic acid is a good starting point (low resolution diagram above).

The hydrogen atoms (protons) of 2-methylpropanoic acid occupy 3 different chemical environments so that the low resolution NMR spectra should show 3 principal peaks of different H-1 NMR chemical shifts (JUST 'blur' the high resolution diagram above for 2-methylpropanoic acid).

CH3CH(CH3)COOH  or  (CH3)2CHCOOH

Note the proton ratio 6:1:1 of the 3 colours of the protons in the 3 chemically different proton environments

Chemical shifts (a) to (c) on the H-1 NMR spectrum diagram for 2-methylpropanoic acid.

Although there are 8 hydrogen atoms in the molecule, there are only 3 possible different 1H chemical environments for the hydrogen atoms in 2-methylpropanoic acid molecule giving 3 different 1H NMR chemical shifts.

The integrated signal proton ratio 6:1:1 observed in the high resolution H-1 NMR spectrum, corresponds with the structural formula of 2-methylpropanoic acid.

The high resolution 1H NMR spectrum of 2-methylpropanoic acid

All low and high resolution spectra of 2-methylpropanoic acid show 3 groups of proton resonances and in the 6:1:1 ratio expected from the structural formula of 2-methylpropanoic acid.

The ppm quoted on the diagram represent the peak of resonance intensity for a particular proton group in the molecule of 2-methylpropanoic acid - 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 2-methylpropanoic acid below.

So, using the chemical shifts and applying the n+1 rule to 2-methylpropanoic acid and make some predictions using some colour coding! (In problem solving you work the other way round!)

(a) 1H Chemical shift 1.20 ppm, six methyl protons: (CH3)2CHCOOH

This resonance is split into a doublet by the CH proton (n+1 = 2).

Evidence for the presence of a CH group in the molecule of 2-methylpropanoic acid

(b) 1H Chemical shift 2.58 ppm, CH alkyl proton: (CH3)2CHCOOH

This resonance is split into a 1:6:15:20:15:6:1 septet by the two groups of methyl protons (n+6 = 7).

Evidence for the presence of a CH3-CH-CH3 group in the molecule of 2-methylpropanoic acid

(c) 1H Chemical shift 11.88 ppm, hydroxyl proton: (CH3)2CHCOOH

This resonance is observed as a singlet because there is no proton on an adjacent carbon atom (n+0 = 1).

Evidence for the presence of an 'isolated' proton in the molecule of 2-methylpropanoic acid.

The chemical shift indicates a hydroxyl proton.

Note the decreasing effect on the 1H chemical shift as the proton is further from the more electronegative oxygen atoms in 2-methylpropanoic acid.

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 2-methylpropanoic acid.
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 (CH3)2CHCOOH Interpreting the proton H-1 NMR spectra of 2-methylpropanoic acid, low resolution & high resolution proton nmr spectra of 2-methylpropanoic acid, H-1 nmr spectrum of 2-methylpropanoic acid, understanding the hydrogen-1 nmr spectrum of 2-methylpropanoic acid, explaining the line splitting patterns from spin-spin coupling  in the high resolution H-1 nmr spectra of 2-methylpropanoic acid, revising the H-1 nmr spectrum of 2-methylpropanoic acid, proton nmr of 2-methylpropanoic acid, ppm chemical shifts of the H-1 nmr spectrum of 2-methylpropanoic acid, 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 2-methylpropanoic acid, how to work out the number of chemically different protons in the structure of the 2-methylpropanoic acid organic molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR spectrum of 2-methylpropanoic acid using the n+1 rule to explain the spin - spin coupling ine splitting in the proton nmr spectrum of 2-methylpropanoic acid deducing the nature of the protons from the chemical shifts ppm in the H-1 nmr spectrum of 2-methylpropanoic acid examining the 1H nmr spectrum of  2-methylpropanoic acid analysing the 1-H nmr spectrum of 2-methylpropanoic acid how do you sketch and interpret the H-1 NMR spectrum of 2-methylpropanoic acid interpreting interpretation of the 1H proton spin-spin coupling causing line splitting in the NMR spectrum of 2-methylpropanoic acid  assignment of chemical shifts in the proton 1H NMR spectrum of 2-methylpropanoic acid formula explaining spin-spin coupling for line splitting for 2-methylpropanoic acid isobutyric acid carboxylic acid functional group How do you interpret the H-1 NMR spectrum of 2-methylpropanoic acid How to interpret the H-1 NMR spectrum of 2-methylpropanoic acid Explanatory diagram of the chemical shifts of the 1H H-1 proton NMR spectrum of the 2-methylpropanoic acid molecule in terms of its molecular structure. Listing data of all the chemical shift peaks in ppm in the proton NMR spectrum of 2-methylpropanoic acid. How to explain the H-1 NMR spectrum of 2-methylpropanoic acid. The chemical shifts and  integrated values of the proton ratios in the 1-H NMR spectrum of the 2-methylpropanoic acid molecule. How to work out the molecular structure of the 2-methylpropanoic acid molecule from its proton NMR spectrum. The uses and distinctive features of the proton NMR spectrum of the 2-methylpropanoic acid molecule explained. What does the H-1 proton NMR spectrum chemical shifts tell us about the structure and properties of the 2-methylpropanoic acid molecule? explaining the spin-spin proton coupling effects in the 1H NMR spectrum of 2-methylpropanoic acid. 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 2-methylpropanoic acid

Links associated with 2-methylpropanoic acid

The infrared spectrum of 2-methylpropanic acid (isobutyric acid)

The mass spectrum of 2-methylpropanic acid (isobutyric acid)

The C-13 NMR spectrum of 2-methylpropanic acid (isobutyric acid)

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H-1 proton NMR spectroscopy index  (Please read 8 points at the top of the 1H NMR index page)

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