Advanced Organic Chemistry: 1H NMR spectrum of 2-methylpropanal (CH3)2CHCHO

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Interpreting and explaining the H-1 NMR spectrum of 2-methylpropanal (iso-butyraldehyde)

[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-methylpropanal (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-methylpropanal

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

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

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

low/high resolution 1H proton nmr spectrum of 2-methylpropanal C4H8O (CH3)2CHCHO analysis interpretation of chemical shifts ppm spin spin line splitting diagram H1 H-1 nmr for isobutyraldehyde 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-methylpropanal here.

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

2-methylpropanal   C4H8O   aldehydes and ketones nomenclature (c) doc b    aldehydes and ketones nomenclature (c) doc b    aldehydes and ketones nomenclature (c) doc b

The molecular structure and naming of aldehydes and ketones

Interpreting the H-1 NMR spectrum of 2-methylpropanal

In terms of spin-spin coupling from the possible proton magnetic orientations, for 2-methylpropanal I have only considered the interactions of non-equivalent protons on adjacent carbon atoms e.g. -CH-CH3, R-CH-CH2- protons etc.

For relatively simple molecules, the low resolution H-1 NMR spectrum of 2-methylpropanal is a good starting point and would show protons in the ratio 6:1:1.

The hydrogen atoms (protons) of 2-methylpropanal occupy 3 different chemical environments so that the low resolution NMR spectra should show 3 principal 1H peaks of different H-1 NMR chemical shifts (I've only constructed the diagram above for 2-methylpropanal).

(CH3)2CHCHO

Note the proton ratio 6:1:1 of the 3 colours of the protons in the 3 chemically different environments and the integrated signal proton ratio observed in the high resolution H-1 NMR spectrum, corresponds with the structural formula of 2-methylpropanal.

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

Although there are 8 hydrogen atoms in the molecule, there are only 3 possible different chemical environments for the hydrogen atoms in 2-methylpropanal molecule.

The high resolution 1H NMR spectrum of 2-methylpropanal - tricky in places!

All low and high resolution spectra of 2-methylpropanal show 3 groups of proton resonances and in the ? ratio expected from the formula of 2-methylpropanal.

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

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

(a) 1H Chemical shift 1.06 ppm, methyl protons: (CH3)2CHCHO

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

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

(b) 1H Chemical shift 2.39 ppm, CH proton of the alkyl group: (CH3)2CHCHO

You might think that this 1H NMR resonance is split into an octet by the adjacent CH3 (x 2) and CH protons (n+1 = 8), but this is not so!

You are dealing with two coincidence splittings. This CH proton resonance is split by the other 2 x CH3 protons into a septet (n+1 = 7), which is then split into doublets by the CH (aldehyde proton), giving seven doublets (n+1 = 2).

(This is more university level NMR spectroscopy, so don't worry, concentrate on the basic proton ratio of 6:1:1 to match the structure of 2-methylpropanal).

(c) 1H Chemical shift 9.57 ppm, CH proton of the aldehyde group: (CH3)2CHCHO

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

Note the large chemical shift exhibited by the aldehyde group proton (much more than the other CH proton).

Evidence for the presence of a 2nd CH group in the molecule of 2-methylpropanal

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

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-methylpropanal.
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

7 protons create a resonance split of a 1:7:21:35:35:21:7:1 octet.

Key words & phrases: C4H8O (CH3)2CHCHO Interpreting the proton H-1 NMR spectra of 2-methylpropanal, low resolution & high resolution proton nmr spectra of 2-methylpropanal, H-1 nmr spectrum of 2-methylpropanal, understanding the hydrogen-1 nmr spectrum of 2-methylpropanal, explaining the line splitting patterns from spin-spin coupling  in the high resolution H-1 nmr spectra of 2-methylpropanal, revising the H-1 nmr spectrum of 2-methylpropanal, proton nmr of 2-methylpropanal, ppm chemical shifts of the H-1 nmr spectrum of 2-methylpropanal, 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-methylpropanal, how to work out the number of chemically different protons in the structure of the 2-methylpropanal organic molecule, how to analyse the chemical shifts in the hydrogen-1 H-1 proton NMR spectrum of 2-methylpropanal using the n+1 rule to explain the spin - spin coupling ine splitting in the proton nmr spectrum of 2-methylpropanal deducing the nature of the protons from the chemical shifts ppm in the H-1 nmr spectrum of 2-methylpropanal examining the 1H nmr spectrum of  2-methylpropanal analysing the 1-H nmr spectrum of 2-methylpropanal how do you sketch and interpret the H-1 NMR spectrum of 2-methylpropanal interpreting interpretation of the 1H proton spin-spin coupling causing line splitting in the NMR spectrum of 2-methylpropanal  assignment of chemical shifts in the proton 1H NMR spectrum of 2-methylpropanal formula explaining spin-spin coupling for line splitting for  methylpropanal iso-butyraldehyde 2-methylpropionaldehyde iso-butyraldehyde Molecular structure diagram of the proton NMR diagram for the 1H NMR spectrum of 2-methylpropanal. The proton ratio in the 1H NMR spectrum of 2-methylpropanal. Deducing the number of different chemical environments of the protons in the 2-methylpropanal molecule from the 1H chemical shifts in the hydrogen-1 NMR spectrum of 2-methylpropanal. Analysing the high resolution 1H NMR spectrum of 2-methylpropanal. Analysing the low resolution 1H NMR spectrum of 2-methylpropanal. You may need to know the relative molecular mass of 2-methylpropanal to deduce the molecular formula from the proton ratio of the 1H NMR spectrum of 2-methylpropanal. Revision notes on the proton NMR spectrum of 2-methylpropanal. Matching and deducing the structure of the 2-methylpropanal molecule from its hydrogen-1 NMR spectrum. How do you interpret the H-1 NMR spectrum of 2-methylpropanal How to interpret the H-1 NMR spectrum of 2-methylpropanal Explanatory diagram of the chemical shifts of the 1H H-1 proton NMR spectrum of the 2-methylpropanal molecule in terms of its molecular structure. Listing data of all the chemical shift peaks in ppm in the proton NMR spectrum of 2-methylpropanal. How to explain the H-1 NMR spectrum of 2-methylpropanal. The chemical shifts and  integrated values of the proton ratios in the 1-H NMR spectrum of the 2-methylpropanal molecule. How to work out the molecular structure of the 2-methylpropanal molecule from its proton NMR spectrum. The uses and distinctive features of the proton NMR spectrum of the 2-methylpropanal molecule explained. What does the H-1 proton NMR spectrum chemical shifts tell us about the structure and properties of the 2-methylpropanal molecule? explaining the spin-spin proton coupling effects in the 1H NMR spectrum of 2-methylpropanal. 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-methylpropanal

Links associated with 2-methylpropanal

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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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