butanal low high resolution H-1 proton nmr spectrum of butyraldehyde analysis interpretation of chemical shifts ppm spin spin line splitting H1 1-H nmr doc brown's advanced organic chemistry revision notes

Advanced Organic Chemistry: H-1 NMR spectrum of butanal (butyraldehyde) CH₃CH₂CH₂CHO

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Interpreting the H-1 (proton) NMR spectrum of butanal (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 butanal [updated Mar 20th 2026 *]

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H-1 proton NMR spectroscopy - spectra index

Introductory note on the 1H NMR spectra of butanal

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

The chemical shift δ splitting pattern effects for butanal 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 butanal molecule).

It is assumed that the integrated intensities of the ¹H NMR δ chemical shifts give the ratio of the protons in the different non-equivalent chemical environments of the butanal molecule.

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

H-1 nmr spectrum of butanal analysis of chemical shifts ppm interpretation of proton chemical shifts ppm of butyraldehyde 1-H proton nmr 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 - butanal here.

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

butanal (butyraldehyde), C₄H₈O, , , aldehyde

The molecular structure and naming of aldehydes and ketones
Interpreting the H-1 NMR spectrum of butanal

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

The hydrogen atoms (protons) of butanal occupy 4 different chemical environments so that the low resolution NMR spectra should show 4 peaks of different H-1 NMR chemical shifts (diagram above for butanal).

CH₃CH₂CH₂CHO

Note the ratio 3:2:2:1 of the four colours of the protons in the four chemically different environments

Although there are 8 hydrogen atoms in the molecule, there only three possible chemical environments for the hydrogen atoms in butanal molecule.

The proton ratio 3:2:2:1 observed, corresponds with the structural molecular formula of butanal.

The very high resolution spectrum of butanal - tricky in places!

CH₃CH₂CH₂CHO

All low and high resolution spectra of butanal show four groups of protons and in the 3:2:2:1 ratio expected from the molecular structure of butanal. The ppm quoted represent the peak of resonance intensity for a particular proton group in the molecule of butanal.

(a) The 0.97 ppm ¹H NMR chemical shift: CH₃CH₂CH₂CHO

The adjacent CH₂ protons split the CH₃ proton resonance into a 1:2:1 triplet (n+1 = 3).

Evidence of a CH₂ group in the butanal molecule.

(b) The 1.64 ppm ¹H NMR chemical shift: CH₃CH₂CH₂CHO

From the n+1 rule, the 'left-hand' CH₂ protons (H₂) are split by adjacent CH₃ protons (H₃) and by the other adjacent CH₂ protons (H₂), (5 protons in total), into a 1:5:10:10:5:1 sextet of resonance lines (n+1 = 6).

This is pattern of resonances is a good indication of a propyl group (CH₃CH₂CH₂) and the sextet is clearly seen on the very high resolution spectrum diagram of butanal above.

(c) The 2.37 ppm ¹H NMR chemical shift: CH₃CH₂CH₂CHO

You might think that the middle right-hand CH₂ protons (H₂) are split on the left sides by CH₂ protons (H₂) and on the right by the CH proton (H), (3 protons in total), so you would a 1:3:3:1 quartet of resonance lines, but this is not so!

This CH₂ proton resonance is split by the other adjacent CH₂ protons into a triplet, which is then split into doublets by the CH (aldehyde proton), giving a series of 1:2:1 doublets - from what I can gather from the internet, its even more complicated than this.

(This is more university level NMR spectroscopy, so don't worry, concentrate on the basic proton ratio of 3:2:2:1 to match the structure of butanal).

(d) The 9.76 ppm ¹H NMR chemical shift: CH₃CH₂CH₂CHO

The adjacent CH₂ protons split the CH proton (of the aldehyde group) resonance into a 1:2:1 triplet.

Evidence of a 2nd CH₂ group in the butanal molecule.

Note the much higher chemical shift for the proton nearest the very electronegative oxygen atom.

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).

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

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

Links associated with butanal

The chemistry of ALDEHYDES and KETONES revision notes INDEX

The infrared spectrum of Butanal

The mass spectrum of Butanal

The C-13 NMR spectrum of Butanal

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

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